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[patch 14/19] datasheet implementation


From: blp
Subject: [patch 14/19] datasheet implementation
Date: Tue, 05 Jun 2007 23:27:41 -0700
User-agent: quilt/0.45-1

This is the datasheet code to provide a flexible backing store for the
GUI's active file.

The name's not the best.  I'm willing to change it.

Need to chmod a+x tests/command/datasheet.sh after applying this patch.

After this patch everything compiles, but linking fails because
casereader_clone and some other casereader symbols are duplicates.
The next patch removes casefile.c from the build and fixes the
problem.

Index: merge/src/data/automake.mk
===================================================================
--- merge.orig/src/data/automake.mk     2007-06-04 21:46:10.000000000 -0700
+++ merge/src/data/automake.mk  2007-06-04 21:52:06.000000000 -0700
@@ -45,6 +45,8 @@
        src/data/data-in.h \
        src/data/data-out.c \
        src/data/data-out.h \
+       src/data/datasheet.c \
+       src/data/datasheet.h \
        src/data/dictionary.c \
        src/data/dictionary.h \
        src/data/file-handle-def.c \
Index: merge/src/data/datasheet.c
===================================================================
--- /dev/null   1970-01-01 00:00:00.000000000 +0000
+++ merge/src/data/datasheet.c  2007-06-04 21:55:15.000000000 -0700
@@ -0,0 +1,1591 @@
+/* PSPP - computes sample statistics.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA. */
+
+#include <config.h>
+
+#include <data/datasheet.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <data/casereader-provider.h>
+#include <data/casereader.h>
+#include <data/casewriter.h>
+#include <data/sparse-cases.h>
+#include <libpspp/array.h>
+#include <libpspp/assertion.h>
+#include <libpspp/model-checker.h>
+#include <libpspp/range-map.h>
+#include <libpspp/range-set.h>
+#include <libpspp/taint.h>
+#include <libpspp/tower.h>
+
+#include "minmax.h"
+#include "md4.h"
+#include "xalloc.h"
+
+static struct axis *axis_create (void);
+static struct axis *axis_clone (const struct axis *);
+static void axis_destroy (struct axis *);
+
+static void axis_hash (const struct axis *, struct md4_ctx *);
+
+static bool axis_allocate (struct axis *, unsigned long int request,
+                           unsigned long int *start,
+                           unsigned long int *width);
+static void axis_make_available (struct axis *,
+                                unsigned long int start,
+                                unsigned long int width);
+static unsigned long int axis_extend (struct axis *, unsigned long int width);
+
+static unsigned long int axis_map (const struct axis *, unsigned long log_pos);
+
+static unsigned long axis_get_size (const struct axis *);
+static void axis_insert (struct axis *,
+                         unsigned long int log_start,
+                         unsigned long int phy_start,
+                         unsigned long int cnt);
+static void axis_remove (struct axis *,
+                         unsigned long int start, unsigned long int cnt);
+static void axis_move (struct axis *,
+                       unsigned long int old_start,
+                       unsigned long int new_start,
+                       unsigned long int cnt);
+
+static struct source *source_create_empty (size_t column_cnt);
+static struct source *source_create_casereader (struct casereader *);
+static struct source *source_clone (const struct source *);
+static void source_destroy (struct source *);
+
+static casenumber source_get_backing_row_cnt (const struct source *);
+static size_t source_get_column_cnt (const struct source *);
+
+static bool source_read (const struct source *, 
+                         casenumber row, size_t column,
+                         union value[], size_t value_cnt);
+static bool source_write (struct source *, 
+                          casenumber row, size_t column,
+                          const union value[], size_t value_cnt);
+static bool source_write_columns (struct source *, size_t start_column,
+                                  const union value[], size_t value_cnt);
+static bool source_has_backing (const struct source *);
+static void source_increase_use (struct source *, size_t delta);
+static void source_decrease_use (struct source *, size_t delta);
+static bool source_in_use (const struct source *);
+
+/* A datasheet is internally composed from a set of data files,
+   called "sources".  The sources that make up a datasheet must
+   have the same number of rows (cases), but their numbers of
+   columns (variables) may vary.
+
+   A datasheet's external view is produced by mapping (permuting
+   and selecting) its internal data.  Thus, we can rearrange or
+   delete rows or columns simply by modifying the mapping.  We
+   add rows by adding rows to each source and to the row mapping.
+   We add columns by adding a new source, then adding that source
+   to the column mapping.
+
+   Each source in a datasheet can be a casereader or a
+   sparse_cases.  Casereaders are read-only, so when sources made
+   from casereaders need to be modified, it is done "virtually"
+   through being overlaid by a sparse_cases. */
+
+/* A datasheet. */
+struct datasheet
+  {
+    /* Mappings from logical to physical columns/rows. */
+    struct axis *columns;
+    struct axis *rows;
+
+    /* Mapping from physical columns to "source_info"s. */
+    struct range_map sources;
+
+    /* Minimum number of columns to put in a new source when we
+       need new columns and none are free.  We double it whenever
+       we add a new source to keep the number of file descriptors
+       needed by the datasheet to a minimum, reducing the
+       likelihood of running out. */
+    unsigned column_min_alloc;
+
+    /* Indicates corrupted data in the datasheet. */
+    struct taint *taint;
+  };
+
+/* Maps from a range of physical columns to a source. */
+struct source_info 
+  {
+    struct range_map_node column_range;
+    struct source *source;
+  };
+
+/* Is this operation a read or a write? */
+enum rw_op 
+  {
+    OP_READ,
+    OP_WRITE
+  };
+
+static void free_source_info (struct datasheet *, struct source_info *);
+static struct source_info *source_info_from_range_map (
+  struct range_map_node *);
+static bool rw_case (struct datasheet *ds, enum rw_op op,
+                     casenumber lrow, size_t start_column, size_t column_cnt,
+                     union value data[]);
+
+/* Creates and returns a new datasheet.
+
+   If READER is nonnull, then the datasheet initially contains
+   the contents of READER. */
+struct datasheet *
+datasheet_create (struct casereader *reader) 
+{
+  /* Create datasheet. */
+  struct datasheet *ds = xmalloc (sizeof *ds);
+  ds->columns = axis_create ();
+  ds->rows = axis_create ();
+  range_map_init (&ds->sources);
+  ds->column_min_alloc = 1;
+  ds->taint = taint_create ();
+
+  /* Add backing. */
+  if (reader != NULL) 
+    {
+      size_t column_cnt;
+      casenumber row_cnt;
+      struct source_info *si;
+
+      si = xmalloc (sizeof *si);
+      si->source = source_create_casereader (reader);
+      column_cnt = source_get_column_cnt (si->source);
+      row_cnt = source_get_backing_row_cnt (si->source);
+      source_increase_use (si->source, column_cnt);
+
+      if ( column_cnt > 0 )
+       {
+         unsigned long int column_start;
+      column_start = axis_extend (ds->columns, column_cnt);
+      axis_insert (ds->columns, 0, column_start, column_cnt);
+      range_map_insert (&ds->sources, column_start, column_cnt,
+                        &si->column_range);
+       }
+
+      if ( row_cnt > 0 )
+       {
+         unsigned long int row_start;
+      row_start = axis_extend (ds->rows, row_cnt);
+      axis_insert (ds->rows, 0, row_start, row_cnt);
+       }
+    }
+
+  return ds;
+}
+
+/* Destroys datasheet DS. */
+void
+datasheet_destroy (struct datasheet *ds) 
+{
+  if (ds == NULL)
+    return;
+
+  axis_destroy (ds->columns);
+  axis_destroy (ds->rows);
+  while (!range_map_is_empty (&ds->sources)) 
+    {
+      struct range_map_node *r = range_map_first (&ds->sources);
+      struct source_info *si = source_info_from_range_map (r);
+      free_source_info (ds, si);
+    }
+  taint_destroy (ds->taint);
+  free (ds);
+}
+
+/* Moves datasheet DS to a new location in memory, and returns
+   the new location.  Afterward, the datasheet must not be
+   accessed at its former location.
+
+   This function is useful for ensuring that all references to a
+   datasheet have been dropped, especially in conjunction with
+   tools like Valgrind. */
+struct datasheet *
+datasheet_rename (struct datasheet *ds) 
+{
+  struct datasheet *new = xmemdup (ds, sizeof *ds);
+  free (ds);
+  return new;
+}
+
+/* Returns true if a I/O error has occurred while processing a
+   datasheet operation. */
+bool
+datasheet_error (const struct datasheet *ds) 
+{
+  return taint_is_tainted (ds->taint);
+}
+
+void
+datasheet_force_error (struct datasheet *ds) 
+{
+  taint_set_taint (ds->taint);
+}
+
+const struct taint *
+datasheet_get_taint (const struct datasheet *ds) 
+{
+  return ds->taint;
+}
+
+/* Returns the number of rows in DS. */
+casenumber
+datasheet_get_row_cnt (const struct datasheet *ds) 
+{
+  return axis_get_size (ds->rows);
+}
+
+/* Returns the number of columns in DS. */
+size_t
+datasheet_get_column_cnt (const struct datasheet *ds) 
+{
+  return axis_get_size (ds->columns);
+}
+
+/* Inserts CNT columns into datasheet DS just before column
+   BEFORE.  Initializes the contents of each row in the inserted
+   columns to the CNT values in INIT_VALUES.
+
+   Returns true if successful, false on failure.  In case of
+   failure, the datasheet is unchanged. */
+bool
+datasheet_insert_columns (struct datasheet *ds,
+                          const union value init_values[], size_t cnt,
+                          size_t before) 
+{
+  size_t added = 0;
+  while (cnt > 0) 
+    {
+      unsigned long first_phy; /* First allocated physical column. */
+      unsigned long phy_cnt;   /* Number of allocated physical columns. */
+
+      /* Allocate physical columns from the pool of available
+         columns. */
+      if (!axis_allocate (ds->columns, cnt, &first_phy, &phy_cnt))
+        {
+          /* No columns were available.  Create a new source and
+             extend the axis to make some new ones available. */
+          struct source_info *si;
+
+          phy_cnt = MAX (cnt, ds->column_min_alloc);
+          first_phy = axis_extend (ds->columns, phy_cnt);
+          ds->column_min_alloc = MIN (65536, ds->column_min_alloc * 2);
+
+          si = xmalloc (sizeof *si);
+          si->source = source_create_empty (phy_cnt);
+          range_map_insert (&ds->sources, first_phy, phy_cnt,
+                            &si->column_range);
+          if (phy_cnt > cnt) 
+            {
+              axis_make_available (ds->columns, first_phy + cnt,
+                                   phy_cnt - cnt);
+              phy_cnt = cnt; 
+            }
+        }
+
+      /* Initialize the columns and insert them into the columns
+         axis. */
+      while (phy_cnt > 0)
+        {
+          struct range_map_node *r; /* Range map holding FIRST_PHY column. */
+          struct source_info *s;    /* Source containing FIRST_PHY column. */
+          size_t source_avail;      /* Number of phys columns available. */
+          size_t source_cnt;        /* Number of phys columns to use. */
+
+          /* Figure out how many columns we can and want to take
+             starting at FIRST_PHY, and then insert them into the
+             columns axis. */
+          r = range_map_lookup (&ds->sources, first_phy);
+          s = source_info_from_range_map (r);
+          source_avail = range_map_node_get_end (r) - first_phy;
+          source_cnt = MIN (phy_cnt, source_avail);
+          axis_insert (ds->columns, before, first_phy, source_cnt);
+
+          /* Initialize the data for those columns in the
+             source. */
+          if (!source_write_columns (s->source,
+                                     first_phy - range_map_node_get_start (r),
+                                     init_values, source_cnt)) 
+            {
+              datasheet_delete_columns (ds, before - added,
+                                        source_cnt + added);
+              taint_set_taint (ds->taint);
+              return false;
+            }
+          source_increase_use (s->source, source_cnt);
+
+          /* Advance. */
+          phy_cnt -= source_cnt;
+          first_phy += source_cnt;
+          init_values += source_cnt;
+          cnt -= source_cnt;
+          before += source_cnt;
+          added += source_cnt;
+        }
+    }
+  return true;
+}
+
+/* Deletes the CNT columns in DS starting from column START. */
+void
+datasheet_delete_columns (struct datasheet *ds, size_t start, size_t cnt) 
+{
+  size_t lcol;
+
+  /* Free up columns for reuse. */
+  for (lcol = start; lcol < start + cnt; lcol++)
+    {
+      size_t pcol = axis_map (ds->columns, lcol);
+      struct range_map_node *r = range_map_lookup (&ds->sources, pcol);
+      struct source_info *si = source_info_from_range_map (r);
+
+      source_decrease_use (si->source, 1);
+      if (source_has_backing (si->source))
+        {
+          if (!source_in_use (si->source))
+            free_source_info (ds, si);
+        }
+      else 
+        axis_make_available (ds->columns, pcol, 1);
+    }
+
+  /* Remove columns from logical-to-physical mapping. */
+  axis_remove (ds->columns, start, cnt);
+}
+
+/* Moves the CNT columns in DS starting at position OLD_START so
+   that they then start at position NEW_START.  Equivalent to
+   deleting the column rows, then inserting them at what becomes
+   position NEW_START after the deletion.*/
+void
+datasheet_move_columns (struct datasheet *ds,
+                        size_t old_start, size_t new_start,
+                        size_t cnt) 
+{
+  axis_move (ds->columns, old_start, new_start, cnt);
+}
+
+/* Retrieves the contents of the given ROW in datasheet DS into
+   newly created case C.  Returns true if successful, false on
+   I/O error. */
+bool
+datasheet_get_row (const struct datasheet *ds, casenumber row, struct ccase *c)
+{
+  size_t column_cnt = datasheet_get_column_cnt (ds);
+  case_create (c, column_cnt);
+  if (rw_case ((struct datasheet *) ds, OP_READ,
+               row, 0, column_cnt, case_data_all_rw (c)))
+    return true;
+  else 
+    {
+      case_destroy (c);
+      return false;
+    }
+}
+     
+/* Stores the contents of case C, which is destroyed, into the
+   given ROW in DS.  Returns true on success, false on I/O error.
+   On failure, the given ROW might be partially modified or
+   corrupted. */
+bool
+datasheet_put_row (struct datasheet *ds, casenumber row, struct ccase *c)
+{
+  size_t column_cnt = datasheet_get_column_cnt (ds);
+  bool ok = rw_case (ds, OP_WRITE, row, 0, column_cnt,
+                     (union value *) case_data_all (c));
+  case_destroy (c);
+  return ok;
+}
+
+/* Stores the values of the WIDTH columns in DS in the given ROW
+   starting at COLUMN in DS into VALUES.  Returns true if
+   successful, false on I/O error. */
+bool
+datasheet_get_value (const struct datasheet *ds, casenumber row, size_t column,
+                     union value *value, int width) 
+{
+  return rw_case ((struct datasheet *) ds,
+                  OP_READ, row, column, value_cnt_from_width (width), value);
+}
+
+/* Stores the WIDTH given VALUES into the given ROW in DS
+   starting at COLUMN.  Returns true if successful, false on I/O
+   error.  On failure, the given ROW might be partially modified
+   or corrupted. */
+bool
+datasheet_put_value (struct datasheet *ds, casenumber row, size_t column,
+                     const union value *value, int width)
+{
+  return rw_case (ds, OP_WRITE, row, column, value_cnt_from_width (width),
+                  (union value *) value);
+}
+
+/* Inserts the CNT cases at C, which are destroyed, into
+   datasheet DS just before row BEFORE.  Returns true if
+   successful, false on I/O error.  On failure, datasheet DS is
+   not modified. */
+bool
+datasheet_insert_rows (struct datasheet *ds,
+                       casenumber before, struct ccase c[],
+                       casenumber cnt) 
+{
+  casenumber added = 0;
+  while (cnt > 0) 
+    {
+      unsigned long first_phy;
+      unsigned long phy_cnt;
+      unsigned long i;
+
+      /* Allocate physical rows from the pool of available
+         rows. */
+      if (!axis_allocate (ds->rows, cnt, &first_phy, &phy_cnt)) 
+        {
+          /* No rows were available.  Extend the row axis to make
+             some new ones available. */
+          phy_cnt = cnt;
+          first_phy = axis_extend (ds->rows, cnt); 
+        }
+
+      /* Insert the new rows into the row mapping. */
+      axis_insert (ds->rows, before, first_phy, phy_cnt);
+
+      /* Initialize the new rows. */
+      for (i = 0; i < phy_cnt; i++)
+        if (!datasheet_put_row (ds, before + i, &c[i]))
+          {
+            while (++i < cnt)
+              case_destroy (&c[i]);
+            datasheet_delete_rows (ds, before - added, phy_cnt + added);
+            return false;
+          }
+
+      /* Advance. */
+      c += phy_cnt;
+      cnt -= phy_cnt;
+      before += phy_cnt;
+      added += phy_cnt;
+    }
+  return true;
+}
+
+/* Deletes the CNT rows in DS starting from row FIRST. */
+void
+datasheet_delete_rows (struct datasheet *ds,
+                       casenumber first, casenumber cnt) 
+{
+  size_t lrow;
+
+  /* Free up rows for reuse.
+     FIXME: optimize. */
+  for (lrow = first; lrow < first + cnt; lrow++)
+    axis_make_available (ds->rows, axis_map (ds->rows, lrow), 1);
+
+  /* Remove rows from logical-to-physical mapping. */
+  axis_remove (ds->rows, first, cnt);
+}
+
+/* Moves the CNT rows in DS starting at position OLD_START so
+   that they then start at position NEW_START.  Equivalent to
+   deleting the given rows, then inserting them at what becomes
+   position NEW_START after the deletion. */
+void
+datasheet_move_rows (struct datasheet *ds,
+                     size_t old_start, size_t new_start,
+                     size_t cnt) 
+{
+  axis_move (ds->rows, old_start, new_start, cnt);
+}
+
+static const struct casereader_random_class datasheet_reader_class;
+
+/* Creates and returns a casereader whose input cases are the
+   rows in datasheet DS.  From the caller's perspective, DS is
+   effectively destroyed by this operation, such that the caller
+   must not reference it again. */
+struct casereader *
+datasheet_make_reader (struct datasheet *ds) 
+{
+  struct casereader *reader;
+  ds = datasheet_rename (ds);
+  reader = casereader_create_random (datasheet_get_column_cnt (ds),
+                                     datasheet_get_row_cnt (ds),
+                                     &datasheet_reader_class, ds);
+  taint_propagate (datasheet_get_taint (ds), casereader_get_taint (reader));
+  return reader;
+}
+
+static bool
+datasheet_reader_read (struct casereader *reader UNUSED, void *ds_,
+                       casenumber case_idx, struct ccase *c) 
+{
+  struct datasheet *ds = ds_;
+  if (case_idx >= datasheet_get_row_cnt (ds))
+    return false;
+  else if (datasheet_get_row (ds, case_idx, c))
+    return true;
+  else 
+    {
+      taint_set_taint (ds->taint);
+      return false;
+    }
+}
+
+static void
+datasheet_reader_destroy (struct casereader *reader UNUSED, void *ds_)
+{
+  struct datasheet *ds = ds_;
+  datasheet_destroy (ds);
+}
+
+static void
+datasheet_reader_advance (struct casereader *reader UNUSED, void *ds_,
+                          casenumber case_cnt) 
+{
+  struct datasheet *ds = ds_;
+  datasheet_delete_rows (ds, 0, case_cnt);
+}
+
+static const struct casereader_random_class datasheet_reader_class = 
+  {
+    datasheet_reader_read,
+    datasheet_reader_destroy,
+    datasheet_reader_advance,
+  };
+
+/* Removes SI from DS's set of sources and destroys its
+   source. */
+static void
+free_source_info (struct datasheet *ds, struct source_info *si) 
+{
+  range_map_delete (&ds->sources, &si->column_range);
+  source_destroy (si->source);
+  free (si);
+}
+
+static struct source_info *
+source_info_from_range_map (struct range_map_node *node) 
+{
+  return range_map_data (node, struct source_info, column_range);
+}
+
+/* Reads (if OP is OP_READ) or writes (if op is OP_WRITE) the
+   COLUMN_CNT columns starting from column START_COLUMN in row
+   LROW to/from the COLUMN_CNT values in DATA. */
+static bool
+rw_case (struct datasheet *ds, enum rw_op op,
+         casenumber lrow, size_t start_column, size_t column_cnt,
+         union value data[]) 
+{
+  casenumber prow;
+  size_t lcol;
+
+  assert (lrow < datasheet_get_row_cnt (ds));
+  assert (column_cnt <= datasheet_get_column_cnt (ds));
+  assert (start_column + column_cnt <= datasheet_get_column_cnt (ds));
+
+  prow = axis_map (ds->rows, lrow);
+  for (lcol = start_column; lcol < start_column + column_cnt; lcol++, data++)
+    {
+      size_t pcol = axis_map (ds->columns, lcol);
+      struct range_map_node *r = range_map_lookup (&ds->sources, pcol);
+      struct source_info *s = source_info_from_range_map (r);
+      size_t pcol_ofs = pcol - range_map_node_get_start (r);
+      if (!(op == OP_READ
+            ? source_read (s->source, prow, pcol_ofs, data, 1)
+            : source_write (s->source, prow, pcol_ofs, data, 1))) 
+        {
+          taint_set_taint (ds->taint);
+          return false; 
+        }
+    }
+  return true;
+}
+
+/* An axis.
+
+   An axis has two functions.  First, it maintains a mapping from
+   logical (client-visible) to physical (storage) ordinates.  The
+   axis_map and axis_get_size functions inspect this mapping, and
+   the axis_insert, axis_remove, and axis_move functions modify
+   it.  Second, it tracks the set of ordinates that are unused
+   and available for reuse.  (Not all unused ordinates are
+   available for reuse: in particular, unused columns that are
+   backed by a casereader are never reused.)  The axis_allocate,
+   axis_make_available, and axis_extend functions affect the set
+   of available ordinates. */
+struct axis
+  {
+    struct tower log_to_phy;     /* Map from logical to physical ordinates;
+                                    contains "struct axis_group"s. */
+    struct range_set *available; /* Set of unused, available ordinates. */
+    unsigned long int phy_size;  /* Current physical length of axis. */
+  };
+
+/* A mapping from logical to physical ordinates. */
+struct axis_group 
+  {
+    struct tower_node logical;  /* Range of logical ordinates. */
+    unsigned long phy_start;    /* First corresponding physical ordinate. */
+  };
+
+static struct axis_group *axis_group_from_tower_node (struct tower_node *);
+static struct tower_node *make_axis_group (unsigned long int phy_start);
+static struct tower_node *split_axis (struct axis *, unsigned long int where);
+static void merge_axis_nodes (struct axis *, struct tower_node *,
+                              struct tower_node **other_node);
+static void check_axis_merged (const struct axis *axis UNUSED);
+
+/* Creates and returns a new, initially empty axis. */
+static struct axis *
+axis_create (void) 
+{
+  struct axis *axis = xmalloc (sizeof *axis);
+  tower_init (&axis->log_to_phy);
+  axis->available = range_set_create ();
+  axis->phy_size = 0;
+  return axis;
+}
+
+/* Returns a clone of existing axis OLD.
+
+   Currently this is used only by the datasheet model checker
+   driver, but it could be otherwise useful. */
+static struct axis *
+axis_clone (const struct axis *old) 
+{
+  const struct tower_node *node;
+  struct axis *new;
+
+  new = xmalloc (sizeof *new);
+  tower_init (&new->log_to_phy);
+  new->available = range_set_clone (old->available, NULL);
+  new->phy_size = old->phy_size;
+
+  for (node = tower_first (&old->log_to_phy); node != NULL;
+       node = tower_next (&old->log_to_phy, node)) 
+    {
+      unsigned long int size = tower_node_get_height (node);
+      struct axis_group *group = tower_data (node, struct axis_group, logical);
+      tower_insert (&new->log_to_phy, size, make_axis_group (group->phy_start),
+                    NULL);
+    }
+
+  return new;
+}
+
+/* Adds the state of AXIS to the MD4 hash context CTX.
+
+   This is only used by the datasheet model checker driver.  It
+   is unlikely to be otherwise useful. */
+static void
+axis_hash (const struct axis *axis, struct md4_ctx *ctx) 
+{
+  const struct tower_node *tn;
+  const struct range_set_node *rsn;
+
+  for (tn = tower_first (&axis->log_to_phy); tn != NULL;
+       tn = tower_next (&axis->log_to_phy, tn)) 
+    {
+      struct axis_group *group = tower_data (tn, struct axis_group, logical);
+      unsigned long int phy_start = group->phy_start;
+      unsigned long int size = tower_node_get_height (tn);
+
+      md4_process_bytes (&phy_start, sizeof phy_start, ctx);
+      md4_process_bytes (&size, sizeof size, ctx);
+    }
+  
+  for (rsn = range_set_first (axis->available); rsn != NULL;
+       rsn = range_set_next (axis->available, rsn)) 
+    {
+      unsigned long int start = range_set_node_get_start (rsn);
+      unsigned long int end = range_set_node_get_end (rsn);
+      
+      md4_process_bytes (&start, sizeof start, ctx);
+      md4_process_bytes (&end, sizeof end, ctx);
+    }
+
+  md4_process_bytes (&axis->phy_size, sizeof axis->phy_size, ctx);
+}
+
+/* Destroys AXIS. */
+static void
+axis_destroy (struct axis *axis) 
+{
+  if (axis == NULL)
+    return;
+
+  while (!tower_is_empty (&axis->log_to_phy)) 
+    {
+      struct tower_node *node = tower_first (&axis->log_to_phy);
+      struct axis_group *group = tower_data (node, struct axis_group,
+                                             logical);
+      tower_delete (&axis->log_to_phy, node);
+      free (group);
+    }
+
+  range_set_destroy (axis->available);
+  free (axis);
+}
+
+/* Allocates up to REQUEST contiguous unused and available
+   ordinates from AXIS.  If successful, stores the number
+   obtained into *WIDTH and the ordinate of the first into
+   *START, marks the ordinates as now unavailable return true.
+   On failure, which occurs only if AXIS has no unused and
+   available ordinates, returns false without modifying AXIS. */
+static bool
+axis_allocate (struct axis *axis, unsigned long int request,
+               unsigned long int *start, unsigned long int *width) 
+{
+  return range_set_allocate (axis->available, request, start, width);
+}
+
+/* Marks the WIDTH contiguous ordinates in AXIS, starting from
+   START, as unused and available. */
+static void
+axis_make_available (struct axis *axis,
+                     unsigned long int start, unsigned long int width) 
+{
+  range_set_insert (axis->available, start, width);
+}
+
+/* Extends the total physical length of AXIS by WIDTH and returns
+   the first ordinate in the new physical region. */
+static unsigned long int
+axis_extend (struct axis *axis, unsigned long int width) 
+{
+  unsigned long int start = axis->phy_size;
+  axis->phy_size += width;
+  return start;
+}
+
+/* Returns the physical ordinate in AXIS corresponding to logical
+   ordinate LOG_POS.  LOG_POS must be less than the logical
+   length of AXIS. */
+static unsigned long int
+axis_map (const struct axis *axis, unsigned long log_pos) 
+{
+  struct tower_node *node;
+  struct axis_group *group;
+  unsigned long int group_start;
+
+  node = tower_lookup (&axis->log_to_phy, log_pos, &group_start);
+  group = tower_data (node, struct axis_group, logical);
+  return group->phy_start + (log_pos - group_start);
+}
+
+/* Returns the logical length of AXIS. */
+static unsigned long
+axis_get_size (const struct axis *axis) 
+{
+  return tower_height (&axis->log_to_phy);
+}
+
+/* Inserts the CNT contiguous physical ordinates starting at
+   PHY_START into AXIS's logical-to-physical mapping, starting at
+   logical position LOG_START. */
+static void
+axis_insert (struct axis *axis,
+             unsigned long int log_start, unsigned long int phy_start,
+             unsigned long int cnt) 
+{
+  struct tower_node *before = split_axis (axis, log_start);
+  struct tower_node *new = make_axis_group (phy_start);
+  tower_insert (&axis->log_to_phy, cnt, new, before);
+  merge_axis_nodes (axis, new, NULL);
+  check_axis_merged (axis);
+}
+
+/* Removes CNT ordinates from AXIS's logical-to-physical mapping
+   starting at logical position START. */
+static void
+axis_remove (struct axis *axis,
+             unsigned long int start, unsigned long int cnt) 
+{
+  if (cnt > 0) 
+    {
+      struct tower_node *last = split_axis (axis, start + cnt);
+      struct tower_node *cur, *next;
+      for (cur = split_axis (axis, start); cur != last; cur = next) 
+        {
+          next = tower_delete (&axis->log_to_phy, cur);
+          free (axis_group_from_tower_node (cur)); 
+        }
+      merge_axis_nodes (axis, last, NULL);
+      check_axis_merged (axis);
+    }
+}
+
+/* Moves the CNT ordinates in AXIS's logical-to-mapping starting
+   at logical position OLD_START so that they then start at
+   position NEW_START. */
+static void
+axis_move (struct axis *axis,
+           unsigned long int old_start, unsigned long int new_start,
+           unsigned long int cnt) 
+{
+  if (cnt > 0 && old_start != new_start) 
+    {
+      struct tower_node *old_first, *old_last, *new_first;
+      struct tower_node *merge1, *merge2;
+      struct tower tmp_array;
+
+      /* Move ordinates OLD_START...(OLD_START + CNT) into new,
+         separate TMP_ARRAY. */
+      old_first = split_axis (axis, old_start);
+      old_last = split_axis (axis, old_start + cnt);
+      tower_init (&tmp_array);
+      tower_splice (&tmp_array, NULL,
+                    &axis->log_to_phy, old_first, old_last);
+      merge_axis_nodes (axis, old_last, NULL);
+      check_axis_merged (axis);
+
+      /* Move TMP_ARRAY to position NEW_START. */
+      new_first = split_axis (axis, new_start);
+      merge1 = tower_first (&tmp_array);
+      merge2 = tower_last (&tmp_array);
+      if (merge2 == merge1)
+        merge2 = NULL;
+      tower_splice (&axis->log_to_phy, new_first, &tmp_array, old_first, NULL);
+      merge_axis_nodes (axis, merge1, &merge2);
+      merge_axis_nodes (axis, merge2, NULL);
+      check_axis_merged (axis);
+    }
+}
+
+/* Returns the axis_group in which NODE is embedded. */
+static struct axis_group *
+axis_group_from_tower_node (struct tower_node *node) 
+{
+  return tower_data (node, struct axis_group, logical);
+}
+
+/* Creates and returns a new axis_group at physical position
+   PHY_START. */
+static struct tower_node *
+make_axis_group (unsigned long phy_start) 
+{
+  struct axis_group *group = xmalloc (sizeof *group);
+  group->phy_start = phy_start;
+  return &group->logical;
+}
+
+/* Returns the tower_node in AXIS's logical-to-physical map whose
+   bottom edge is at exact level WHERE.  If there is no such
+   tower_node in AXIS's logical-to-physical map, then split_axis
+   creates one by breaking an existing tower_node into two
+   separate ones, unless WHERE is equal to the tower height, in
+   which case it simply returns a null pointer. */
+static struct tower_node *
+split_axis (struct axis *axis, unsigned long int where) 
+{
+  unsigned long int group_start;
+  struct tower_node *group_node;
+  struct axis_group *group;
+
+  assert (where <= tower_height (&axis->log_to_phy));
+  if (where >= tower_height (&axis->log_to_phy))
+    return NULL;
+
+  group_node = tower_lookup (&axis->log_to_phy, where, &group_start);
+  group = axis_group_from_tower_node (group_node);
+  if (where > group_start) 
+    {
+      unsigned long int size_1 = where - group_start;
+      unsigned long int size_2 = tower_node_get_height (group_node) - size_1;
+      struct tower_node *next = tower_next (&axis->log_to_phy, group_node);
+      struct tower_node *new = make_axis_group (group->phy_start + size_1);
+      tower_resize (&axis->log_to_phy, group_node, size_1);
+      tower_insert (&axis->log_to_phy, size_2, new, next);
+      return new;
+    }
+  else
+    return &group->logical;
+}
+
+/* Within AXIS, attempts to merge NODE (or the last node in AXIS,
+   if NODE is null) with its neighbor nodes.  This is possible
+   when logically adjacent nodes are also adjacent physically (in
+   the same order).  
+
+   When a merge occurs, and OTHER_NODE is non-null and points to
+   the node to be deleted, this function also updates
+   *OTHER_NODE, if necessary, to ensure that it remains a valid
+   pointer. */
+static void
+merge_axis_nodes (struct axis *axis, struct tower_node *node,
+                  struct tower_node **other_node)
+{
+  struct tower *t = &axis->log_to_phy;
+  struct axis_group *group;
+  struct tower_node *next, *prev;
+
+  /* Find node to potentially merge with neighbors. */
+  if (node == NULL) 
+    node = tower_last (t);
+  if (node == NULL)
+    return;
+  group = axis_group_from_tower_node (node);
+
+  /* Try to merge NODE with successor. */
+  next = tower_next (t, node);
+  if (next != NULL) 
+    {
+      struct axis_group *next_group = axis_group_from_tower_node (next);
+      unsigned long this_height = tower_node_get_height (node);
+      
+      if (group->phy_start + this_height == next_group->phy_start)
+        {
+          unsigned long next_height = tower_node_get_height (next);
+          tower_resize (t, node, this_height + next_height);
+          if (other_node != NULL && *other_node == next)
+            *other_node = tower_next (t, *other_node);
+          tower_delete (t, next);
+          free (next_group);
+        }
+    }
+
+  /* Try to merge NODE with predecessor. */
+  prev = tower_prev (t, node);
+  if (prev != NULL) 
+    {
+      struct axis_group *prev_group = axis_group_from_tower_node (prev);
+      unsigned long prev_height = tower_node_get_height (prev);
+      
+      if (prev_group->phy_start + prev_height == group->phy_start)
+        {
+          unsigned long this_height = tower_node_get_height (node);
+          group->phy_start = prev_group->phy_start;
+          tower_resize (t, node, this_height + prev_height);
+          if (other_node != NULL && *other_node == prev)
+            *other_node = tower_next (t, *other_node);
+          tower_delete (t, prev);
+          free (prev_group);
+        }
+    }
+}
+
+/* Verify that all potentially merge-able nodes in AXIS are
+   actually merged. */
+static void
+check_axis_merged (const struct axis *axis UNUSED) 
+{
+#if ASSERT_LEVEL >= 10
+  struct tower_node *prev, *node;
+  
+  for (prev = NULL, node = tower_first (&axis->log_to_phy); node != NULL;
+       prev = node, node = tower_next (&axis->log_to_phy, node))
+    if (prev != NULL) 
+      {
+        struct axis_group *prev_group = axis_group_from_tower_node (prev);
+        unsigned long prev_height = tower_node_get_height (prev);
+        struct axis_group *node_group = axis_group_from_tower_node (node);
+        assert (prev_group->phy_start + prev_height != node_group->phy_start);
+      }
+#endif
+}
+
+/* A source. */
+struct source
+  {
+    size_t columns_used;        /* Number of columns in use by client. */
+    struct sparse_cases *data;  /* Data at top level, atop the backing. */
+    struct casereader *backing; /* Backing casereader (or null). */
+    casenumber backing_rows;    /* Number of rows in backing (if nonnull). */
+  };
+
+/* Creates and returns an empty, unbacked source with COLUMN_CNT
+   columns and an initial "columns_used" of 0. */
+static struct source *
+source_create_empty (size_t column_cnt) 
+{
+  struct source *source = xmalloc (sizeof *source);
+  source->columns_used = 0;
+  source->data = sparse_cases_create (column_cnt);
+  source->backing = NULL;
+  source->backing_rows = 0;
+  return source;
+}
+
+/* Creates and returns a new source backed by READER and with the
+   same initial dimensions and content. */
+static struct source *
+source_create_casereader (struct casereader *reader) 
+{
+  struct source *source
+    = source_create_empty (casereader_get_value_cnt (reader));
+  source->backing = reader;
+  source->backing_rows = casereader_count_cases (reader);
+  return source;
+}
+
+/* Returns a clone of source OLD with the same data and backing
+   (if any).
+
+   Currently this is used only by the datasheet model checker
+   driver, but it could be otherwise useful. */
+static struct source *
+source_clone (const struct source *old) 
+{
+  struct source *new = xmalloc (sizeof *new);
+  new->columns_used = old->columns_used;
+  new->data = sparse_cases_clone (old->data);
+  new->backing = old->backing != NULL ? casereader_clone (old->backing) : NULL;
+  new->backing_rows = old->backing_rows;
+  if (new->data == NULL)
+    {
+      source_destroy (new);
+      new = NULL;
+    }
+  return new;
+}
+
+/* Increases the columns_used count of SOURCE by DELTA.
+   The new value must not exceed SOURCE's number of columns. */
+static void
+source_increase_use (struct source *source, size_t delta) 
+{
+  source->columns_used += delta;
+  assert (source->columns_used <= sparse_cases_get_value_cnt (source->data));
+}
+
+/* Decreases the columns_used count of SOURCE by DELTA.
+   This must not attempt to decrease the columns_used count below
+   zero. */
+static void
+source_decrease_use (struct source *source, size_t delta) 
+{
+  assert (delta <= source->columns_used);
+  source->columns_used -= delta;
+}
+
+/* Returns true if SOURCE has any columns in use,
+   false otherwise. */
+static bool
+source_in_use (const struct source *source) 
+{
+  return source->columns_used > 0;
+}
+
+/* Destroys SOURCE and its data and backing, if any. */
+static void
+source_destroy (struct source *source) 
+{
+  if (source != NULL) 
+    {
+      sparse_cases_destroy (source->data);
+      casereader_destroy (source->backing);
+      free (source);
+    }
+}
+
+/* Returns the number of rows in SOURCE's backing casereader
+   (SOURCE must have a backing casereader). */
+static casenumber
+source_get_backing_row_cnt (const struct source *source) 
+{
+  assert (source_has_backing (source));
+  return source->backing_rows;
+}
+
+/* Returns the number of columns in SOURCE. */
+static size_t
+source_get_column_cnt (const struct source *source) 
+{
+  return sparse_cases_get_value_cnt (source->data);
+}
+
+/* Reads VALUE_CNT columns from SOURCE in the given ROW, starting
+   from COLUMN, into VALUES.  Returns true if successful, false
+   on I/O error. */
+static bool
+source_read (const struct source *source, 
+             casenumber row, size_t column,
+             union value values[], size_t value_cnt) 
+{
+  if (source->backing == NULL || sparse_cases_contains_row (source->data, row))
+    return sparse_cases_read (source->data, row, column, values, value_cnt);
+  else
+    {
+      struct ccase c;
+      bool ok;
+      
+      assert (source->backing != NULL);
+      ok = casereader_peek (source->backing, row, &c);
+      if (ok) 
+        {
+          case_copy_out (&c, column, values, value_cnt);
+          case_destroy (&c);
+        }
+      return ok;
+    }
+}
+
+/* Writes the VALUE_CNT values in VALUES to SOURCE in the given
+   ROW, starting at ROW.  Returns true if successful, false on
+   I/O error.  On error, the row's data may be completely or
+   partially corrupted, both inside and outside the region to be
+   written.  */
+static bool
+source_write (struct source *source, 
+              casenumber row, size_t column,
+              const union value values[], size_t value_cnt) 
+{
+  size_t column_cnt = sparse_cases_get_value_cnt (source->data);
+  bool ok;
+
+  if (source->backing == NULL
+      || (column == 0 && value_cnt == column_cnt)
+      || sparse_cases_contains_row (source->data, row)) 
+    ok = sparse_cases_write (source->data, row, column, values, value_cnt);
+  else
+    {
+      struct ccase c;
+      if (row < source->backing_rows)
+        ok = casereader_peek (source->backing, row, &c);
+      else
+        {
+          /* It's not one of the backed rows.  Ideally, this
+             should never happen: we'd always be writing the full
+             contents of new, unbacked rows in a single call to
+             this function, so that the first case above would
+             trigger.  But that's a little difficult at higher
+             levels, so that we in fact usually write the full
+             contents of new, unbacked rows in multiple calls to
+             this function.  Make this work. */
+          case_create (&c, column_cnt);
+          ok = true;
+        }
+      if (ok) 
+        {
+          case_copy_in (&c, column, values, value_cnt);
+          ok = sparse_cases_write (source->data, row, 0,
+                                   case_data_all (&c), column_cnt); 
+          case_destroy (&c);
+        }
+    }
+  return ok;
+}
+
+/* Within SOURCE, which must not have a backing casereader,
+   writes the VALUE_CNT values in VALUES_CNT to the VALUE_CNT
+   columns starting from START_COLUMN, in every row, even in rows
+   not yet otherwise initialized.  Returns true if successful,
+   false if an I/O error occurs.
+
+   We don't support backing != NULL because (1) it's harder and
+   (2) source_write_columns is only called by
+   datasheet_insert_columns, which doesn't reuse columns from
+   sources that are backed by casereaders. */
+static bool
+source_write_columns (struct source *source, size_t start_column,
+                      const union value values[], size_t value_cnt) 
+{
+  assert (source->backing == NULL);
+  
+  return sparse_cases_write_columns (source->data, start_column,
+                                     values, value_cnt);
+}
+
+/* Returns true if SOURCE has a backing casereader, false
+   otherwise. */
+static bool
+source_has_backing (const struct source *source) 
+{
+  return source->backing != NULL;
+}
+
+/* Datasheet model checker test driver. */
+
+/* Maximum size of datasheet supported for model checking
+   purposes. */
+#define MAX_ROWS 5
+#define MAX_COLS 5
+
+/* Hashes the structure of datasheet DS and returns the hash.
+   We use MD4 because it is much faster than MD5 or SHA-1 but its
+   collision resistance is just as good. */
+static unsigned int
+hash_datasheet (const struct datasheet *ds) 
+{
+  unsigned int hash[DIV_RND_UP (20, sizeof (unsigned int))];
+  struct md4_ctx ctx;
+  struct range_map_node *r;
+
+  md4_init_ctx (&ctx);
+  axis_hash (ds->columns, &ctx);
+  axis_hash (ds->rows, &ctx);
+  for (r = range_map_first (&ds->sources); r != NULL;
+       r = range_map_next (&ds->sources, r)) 
+    {
+      unsigned long int start = range_map_node_get_start (r);
+      unsigned long int end = range_map_node_get_end (r);
+      md4_process_bytes (&start, sizeof start, &ctx);
+      md4_process_bytes (&end, sizeof end, &ctx);
+    }
+  md4_process_bytes (&ds->column_min_alloc, sizeof ds->column_min_alloc,
+                      &ctx);
+  md4_finish_ctx (&ctx, hash);
+  return hash[0];
+}
+
+/* Checks that datasheet DS contains has ROW_CNT rows, COLUMN_CNT
+   columns, and the same contents as ARRAY, reporting any
+   mismatches via mc_error.  Then, adds DS to MC as a new state. */
+static void
+check_datasheet (struct mc *mc, struct datasheet *ds,
+                 double array[MAX_ROWS][MAX_COLS],
+                 size_t row_cnt, size_t column_cnt) 
+{
+  assert (row_cnt < MAX_ROWS);
+  assert (column_cnt < MAX_COLS);
+
+  /* If it is a duplicate hash, discard the state before checking
+     its consistency, to save time. */
+  if (mc_discard_dup_state (mc, hash_datasheet (ds)))
+    {
+      datasheet_destroy (ds);
+      return;
+    }
+
+  if (row_cnt != datasheet_get_row_cnt (ds))
+    mc_error (mc, "row count (%lu) does not match expected (%zu)",
+              (unsigned long int) datasheet_get_row_cnt (ds), row_cnt);
+  else if (column_cnt != datasheet_get_column_cnt (ds))
+    mc_error (mc, "column count (%lu) does not match expected (%zu)",
+              (unsigned long int) datasheet_get_column_cnt (ds), column_cnt);
+  else 
+    {
+      size_t row, col;
+
+      for (row = 0; row < row_cnt; row++)
+        for (col = 0; col < column_cnt; col++) 
+          {
+            union value v;
+            if (!datasheet_get_value (ds, row, col, &v, 1))
+              NOT_REACHED ();
+            if (v.f != array[row][col])
+              mc_error (mc, "element %zu,%zu (of %zu,%zu) differs: %g != %g",
+                        row, col, row_cnt, column_cnt, v.f, array[row][col]);
+          }
+    }
+
+  mc_add_state (mc, ds);
+}
+
+/* Extracts the contents of DS into DATA. */
+static void
+extract_data (const struct datasheet *ds, double data[MAX_ROWS][MAX_COLS])
+{
+  size_t column_cnt = datasheet_get_column_cnt (ds);
+  size_t row_cnt = datasheet_get_row_cnt (ds);
+  size_t row, col;
+
+  assert (row_cnt < MAX_ROWS);
+  assert (column_cnt < MAX_COLS);
+  for (row = 0; row < row_cnt; row++)
+    for (col = 0; col < column_cnt; col++) 
+      {
+        union value v;
+        if (!datasheet_get_value (ds, row, col, &v, 1))
+          NOT_REACHED ();
+        data[row][col] = v.f;
+      }
+}
+
+/* Clones the structure and contents of ODS into *DS,
+   and the contents of ODATA into DATA. */
+static void
+clone_model (const struct datasheet *ods, double odata[MAX_ROWS][MAX_COLS],
+             struct datasheet **ds_, double data[MAX_ROWS][MAX_COLS]) 
+{
+  struct datasheet *ds;
+  struct range_map_node *r;
+
+  /* Clone ODS into DS. */
+  ds = *ds_ = xmalloc (sizeof *ds);
+  ds->columns = axis_clone (ods->columns);
+  ds->rows = axis_clone (ods->rows);
+  range_map_init (&ds->sources);
+  for (r = range_map_first (&ods->sources); r != NULL;
+       r = range_map_next (&ods->sources, r)) 
+    {
+      const struct source_info *osi = source_info_from_range_map (r);
+      struct source_info *si = xmalloc (sizeof *si);
+      si->source = source_clone (osi->source);
+      range_map_insert (&ds->sources, range_map_node_get_start (r),
+                        range_map_node_get_width (r), &si->column_range);
+    }
+  ds->column_min_alloc = ods->column_min_alloc;
+  ds->taint = taint_create ();
+
+  /* Clone ODATA into DATA. */
+  memcpy (data, odata, MAX_ROWS * MAX_COLS * sizeof **data);
+}
+
+/* "init" function for struct mc_class. */
+static void
+datasheet_mc_init (struct mc *mc) 
+{
+  struct datasheet_test_params *params = mc_get_aux (mc);
+  struct datasheet *ds;
+
+  if (params->backing_rows == 0 && params->backing_cols == 0) 
+    {
+      /* Create unbacked datasheet. */
+      ds = datasheet_create (NULL);
+      mc_name_operation (mc, "empty datasheet");
+      check_datasheet (mc, ds, NULL, 0, 0);
+    }
+  else 
+    {
+      /* Create datasheet with backing. */
+      struct casewriter *writer;
+      struct casereader *reader;
+      double data[MAX_ROWS][MAX_COLS];
+      int row;
+
+      assert (params->backing_rows > 0 && params->backing_rows <= MAX_ROWS);
+      assert (params->backing_cols > 0 && params->backing_cols <= MAX_COLS);
+
+      writer = mem_writer_create (params->backing_cols);
+      for (row = 0; row < params->backing_rows; row++)
+        {
+          struct ccase c;
+          int col;
+
+          case_create (&c, params->backing_cols);
+          for (col = 0; col < params->backing_cols; col++)
+            {
+              double value = params->next_value++;
+              data[row][col] = value;
+              case_data_rw_idx (&c, col)->f = value;
+            }
+          casewriter_write (writer, &c);
+        }
+      reader = casewriter_make_reader (writer);
+      assert (reader != NULL);
+      
+      ds = datasheet_create (reader);
+      mc_name_operation (mc, "datasheet with (%d,%d) backing",
+                         params->backing_rows, params->backing_cols);
+      check_datasheet (mc, ds, data,
+                       params->backing_rows, params->backing_cols);
+    }
+}
+
+/* "mutate" function for struct mc_class. */
+static void
+datasheet_mc_mutate (struct mc *mc, const void *ods_) 
+{
+  struct datasheet_test_params *params = mc_get_aux (mc);
+
+  const struct datasheet *ods = ods_;
+  double odata[MAX_ROWS][MAX_COLS];
+  double data[MAX_ROWS][MAX_COLS];
+  size_t column_cnt = datasheet_get_column_cnt (ods);
+  size_t row_cnt = datasheet_get_row_cnt (ods);
+  size_t pos, new_pos, cnt;
+
+  extract_data (ods, odata);
+
+  /* Insert all possible numbers of columns in all possible
+     positions. */
+  for (pos = 0; pos <= column_cnt; pos++)
+    for (cnt = 0; cnt <= params->max_cols - column_cnt; cnt++)
+      if (mc_include_state (mc))
+        {
+          struct datasheet *ds;
+          union value new[MAX_COLS];
+          size_t i, j;
+
+          mc_name_operation (mc, "insert %zu columns at %zu", cnt, pos);
+          clone_model (ods, odata, &ds, data);
+
+          for (i = 0; i < cnt; i++) 
+            new[i].f = params->next_value++;
+
+          if (!datasheet_insert_columns (ds, new, cnt, pos))
+            mc_error (mc, "datasheet_insert_columns failed");
+        
+          for (i = 0; i < row_cnt; i++) 
+            {
+              insert_range (&data[i][0], column_cnt, sizeof data[i][0],
+                            pos, cnt);
+              for (j = 0; j < cnt; j++)
+                data[i][pos + j] = new[j].f;
+            }
+
+          check_datasheet (mc, ds, data, row_cnt, column_cnt + cnt);
+        }
+
+  /* Delete all possible numbers of columns from all possible
+     positions. */
+  for (pos = 0; pos < column_cnt; pos++)
+    for (cnt = 0; cnt < column_cnt - pos; cnt++) 
+      if (mc_include_state (mc))
+        {
+          struct datasheet *ds;
+          size_t i;
+
+          mc_name_operation (mc, "delete %zu columns at %zu", cnt, pos);
+          clone_model (ods, odata, &ds, data);
+
+          datasheet_delete_columns (ds, pos, cnt);
+        
+          for (i = 0; i < row_cnt; i++)
+            remove_range (&data[i], column_cnt, sizeof *data[i], pos, cnt);
+
+          check_datasheet (mc, ds, data, row_cnt, column_cnt - cnt);
+        }
+
+  /* Move all possible numbers of columns from all possible
+     existing positions to all possible new positions. */
+  for (pos = 0; pos < column_cnt; pos++)
+    for (cnt = 0; cnt < column_cnt - pos; cnt++)
+      for (new_pos = 0; new_pos < column_cnt - cnt; new_pos++)
+        if (mc_include_state (mc))
+          {
+            struct datasheet *ds;
+            size_t i;
+
+            clone_model (ods, odata, &ds, data);
+            mc_name_operation (mc, "move %zu columns from %zu to %zu",
+                               cnt, pos, new_pos);
+
+            datasheet_move_columns (ds, pos, new_pos, cnt);
+        
+            for (i = 0; i < row_cnt; i++)
+              move_range (&data[i], column_cnt, sizeof data[i][0],
+                          pos, new_pos, cnt);
+
+            check_datasheet (mc, ds, data, row_cnt, column_cnt);
+          }      
+
+  /* Insert all possible numbers of rows in all possible
+     positions. */
+  for (pos = 0; pos <= row_cnt; pos++)
+    for (cnt = 0; cnt <= params->max_rows - row_cnt; cnt++) 
+      if (mc_include_state (mc))
+        {
+          struct datasheet *ds;
+          struct ccase c[MAX_ROWS];
+          size_t i, j;
+
+          clone_model (ods, odata, &ds, data);
+          mc_name_operation (mc, "insert %zu rows at %zu", cnt, pos);
+
+          for (i = 0; i < cnt; i++) 
+            {
+              case_create (&c[i], column_cnt);
+              for (j = 0; j < column_cnt; j++)
+                case_data_rw_idx (&c[i], j)->f = params->next_value++;
+            }
+
+          insert_range (data, row_cnt, sizeof data[pos], pos, cnt);
+          for (i = 0; i < cnt; i++) 
+            for (j = 0; j < column_cnt; j++)
+              data[i + pos][j] = case_num_idx (&c[i], j);
+
+          if (!datasheet_insert_rows (ds, pos, c, cnt))
+            mc_error (mc, "datasheet_insert_rows failed");
+
+          check_datasheet (mc, ds, data, row_cnt + cnt, column_cnt);
+        }
+
+  /* Delete all possible numbers of rows from all possible
+     positions. */
+  for (pos = 0; pos < row_cnt; pos++)
+    for (cnt = 0; cnt < row_cnt - pos; cnt++) 
+      if (mc_include_state (mc))
+        {
+          struct datasheet *ds;
+
+          clone_model (ods, odata, &ds, data);
+          mc_name_operation (mc, "delete %zu rows at %zu", cnt, pos);
+
+          datasheet_delete_rows (ds, pos, cnt);
+
+          remove_range (&data[0], row_cnt, sizeof data[0], pos, cnt);
+
+          check_datasheet (mc, ds, data, row_cnt - cnt, column_cnt);
+        }
+
+  /* Move all possible numbers of rows from all possible existing
+     positions to all possible new positions. */
+  for (pos = 0; pos < row_cnt; pos++)
+    for (cnt = 0; cnt < row_cnt - pos; cnt++)
+      for (new_pos = 0; new_pos < row_cnt - cnt; new_pos++)
+        if (mc_include_state (mc))
+          {
+            struct datasheet *ds;
+
+            clone_model (ods, odata, &ds, data);
+            mc_name_operation (mc, "move %zu rows from %zu to %zu",
+                               cnt, pos, new_pos);
+
+            datasheet_move_rows (ds, pos, new_pos, cnt);
+        
+            move_range (&data[0], row_cnt, sizeof data[0],
+                        pos, new_pos, cnt);
+
+            check_datasheet (mc, ds, data, row_cnt, column_cnt);
+          }      
+}
+
+/* "destroy" function for struct mc_class. */
+static void
+datasheet_mc_destroy (const struct mc *mc UNUSED, void *ds_) 
+{
+  struct datasheet *ds = ds_;
+  datasheet_destroy (ds);
+}
+
+/* Executes the model checker on the datasheet test driver with
+   the given OPTIONS and passing in the given PARAMS, which must
+   point to a modifiable "struct datasheet_test_params".  If any
+   value in PARAMS is out of range, it will be adjusted into the
+   valid range before running the test.
+
+   Returns the results of the model checking run. */
+struct mc_results *
+datasheet_test (struct mc_options *options, void *params_) 
+{
+  struct datasheet_test_params *params = params_;
+  static const struct mc_class datasheet_mc_class =
+    {
+      datasheet_mc_init,
+      datasheet_mc_mutate,
+      datasheet_mc_destroy,
+    };
+
+  params->next_value = 1;
+  params->max_rows = MIN (params->max_rows, MAX_ROWS);
+  params->max_cols = MIN (params->max_cols, MAX_COLS);
+  params->backing_rows = MIN (params->backing_rows, params->max_rows);
+  params->backing_cols = MIN (params->backing_cols, params->max_cols);
+
+  mc_options_set_aux (options, params);
+  return mc_run (&datasheet_mc_class, options);
+}
Index: merge/src/data/datasheet.h
===================================================================
--- /dev/null   1970-01-01 00:00:00.000000000 +0000
+++ merge/src/data/datasheet.h  2007-06-04 21:52:06.000000000 -0700
@@ -0,0 +1,88 @@
+/* PSPP - computes sample statistics.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA. */
+
+#ifndef DATA_DATASHEET_H
+#define DATA_DATASHEET_H 1
+
+#include <data/case.h>
+#include <data/value.h>
+
+struct casereader;
+
+/* A datasheet is a 2-d array of data that may be stored in
+   memory or on disk.  It efficiently supports data storage and
+   retrieval, as well as adding, removing, and rearranging both
+   rows and columns.  */
+
+struct datasheet *datasheet_create (struct casereader *);
+void datasheet_destroy (struct datasheet *);
+struct datasheet *datasheet_rename (struct datasheet *);
+
+bool datasheet_error (const struct datasheet *);
+void datasheet_force_error (struct datasheet *);
+const struct taint *datasheet_get_taint (const struct datasheet *);
+
+struct casereader *datasheet_make_reader (struct datasheet *);
+
+/* Columns. */
+size_t datasheet_get_column_cnt (const struct datasheet *);
+bool datasheet_insert_columns (struct datasheet *,
+                               const union value[], size_t cnt,
+                               size_t before);
+void datasheet_delete_columns (struct datasheet *, size_t start, size_t cnt);
+void datasheet_move_columns (struct datasheet *,
+                             size_t old_start, size_t new_start,
+                             size_t cnt);
+
+/* Rows. */
+casenumber datasheet_get_row_cnt (const struct datasheet *);
+bool datasheet_insert_rows (struct datasheet *,
+                            casenumber before, struct ccase[],
+                            casenumber cnt);
+void datasheet_delete_rows (struct datasheet *,
+                            casenumber first, casenumber cnt);
+void datasheet_move_rows (struct datasheet *,
+                          size_t old_start, size_t new_start,
+                          size_t cnt);
+
+/* Data. */
+bool datasheet_get_row (const struct datasheet *, casenumber, struct ccase *);
+bool datasheet_put_row (struct datasheet *, casenumber, struct ccase *);
+bool datasheet_get_value (const struct datasheet *, casenumber, size_t column,
+                          union value *, int width);
+bool datasheet_put_value (struct datasheet *, casenumber, size_t column,
+                          const union value *, int width);
+
+/* Testing. */
+struct mc_options;
+
+struct datasheet_test_params
+  {
+    /* Parameters. */
+    int max_rows;
+    int max_cols;
+    int backing_rows;
+    int backing_cols;
+
+    /* State. */
+    int next_value;
+  };
+
+struct mc_results *datasheet_test (struct mc_options *options, void *params);
+
+#endif /* data/datasheet.h */
Index: merge/src/language/command.def
===================================================================
--- merge.orig/src/language/command.def 2007-06-04 21:46:10.000000000 -0700
+++ merge/src/language/command.def      2007-06-04 21:52:06.000000000 -0700
@@ -129,6 +129,7 @@
 
 /* Commands for testing PSPP. */
 DEF_CMD (S_ANY, F_TESTING, "DEBUG CASEFILE", cmd_debug_casefile)
+DEF_CMD (S_ANY, F_TESTING, "DEBUG DATASHEET", cmd_debug_datasheet)
 DEF_CMD (S_ANY, F_TESTING, "DEBUG EVALUATE", cmd_debug_evaluate)
 DEF_CMD (S_ANY, F_TESTING, "DEBUG MOMENTS", cmd_debug_moments)
 DEF_CMD (S_ANY, F_TESTING, "DEBUG POOL", cmd_debug_pool)
Index: merge/src/language/tests/automake.mk
===================================================================
--- merge.orig/src/language/tests/automake.mk   2007-06-04 21:46:10.000000000 
-0700
+++ merge/src/language/tests/automake.mk        2007-06-04 21:52:06.000000000 
-0700
@@ -6,9 +6,10 @@
 language_tests_sources = \
        src/language/tests/casefile-test.c \
        src/language/tests/check-model.h \
+       src/language/tests/datasheet-test.c \
+       src/language/tests/float-format.c \
        src/language/tests/moments-test.c \
        src/language/tests/pool-test.c \
-       src/language/tests/float-format.c \
        $(language_tests_built_sources)
 
 all_q_sources += $(language_tests_built_sources:.c=.q)
Index: merge/src/language/tests/datasheet-test.c
===================================================================
--- /dev/null   1970-01-01 00:00:00.000000000 +0000
+++ merge/src/language/tests/datasheet-test.c   2007-06-04 21:52:06.000000000 
-0700
@@ -0,0 +1,104 @@
+/* PSPP - computes sample statistics.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA. */
+
+#include <config.h>
+
+#include <data/datasheet.h>
+
+#include <language/command.h>
+#include <language/lexer/lexer.h>
+#include <language/tests/check-model.h>
+#include <libpspp/array.h>
+#include <libpspp/assertion.h>
+
+#include "error.h"
+#include "xalloc.h"
+
+static bool parse_coordinates (struct lexer *, int *rows, int *cols);
+
+/* Parses and executes the DEBUG DATASHEET command, which runs
+   the model checker on the datasheet data structure.  The
+   command may include a specification of the form
+   MAX=(ROWS,COLS) to specify the maximum size of the data sheet
+   during the model checker run (default: 4x4) or
+   BACKING=(ROWS,COLS) to specify the size of the casereader
+   backing the datasheet (default: no backing).  These may be
+   optionally followed by any of the common model checker option
+   specifications (see check-model.q). */
+int
+cmd_debug_datasheet (struct lexer *lexer, struct dataset *dataset UNUSED) 
+{
+  struct datasheet_test_params params;
+  bool ok;
+
+  params.max_rows = 4;
+  params.max_cols = 4;
+  params.backing_rows = 0;
+  params.backing_cols = 0;
+
+  for (;;) 
+    {
+      if (lex_match_id (lexer, "MAX"))
+        {
+          if (!parse_coordinates (lexer, &params.max_rows, &params.max_cols))
+            return CMD_FAILURE;
+        }
+      else if (lex_match_id (lexer, "BACKING"))
+        {
+          if (!parse_coordinates (lexer,
+                                  &params.backing_rows, &params.backing_cols))
+            return CMD_FAILURE;
+        }
+      else
+        break;
+      lex_match (lexer, '/');
+    }
+  
+  ok = check_model (lexer, datasheet_test, &params);
+  printf ("Datasheet test max(%d,%d) backing(%d,%d) %s.\n",
+          params.max_rows, params.max_cols,
+          params.backing_rows, params.backing_cols,
+          ok ? "successful" : "failed");
+  return ok ? lex_end_of_command (lexer) : CMD_FAILURE;
+}
+
+/* Parses a pair of coordinates with the syntax =(ROWS,COLS),
+   where all of the delimiters are optional, into *ROWS and
+   *COLS.  Returns true if successful, false on parse failure. */
+static bool
+parse_coordinates (struct lexer *lexer, int *rows, int *cols) 
+{
+  lex_match (lexer, '=');
+  lex_match (lexer, '(');
+
+  if (!lex_force_int (lexer))
+    return false;
+  *rows = lex_integer (lexer);
+  lex_get (lexer);
+
+  lex_match (lexer, ',');
+
+  if (!lex_force_int (lexer))
+    return false;
+  *cols = lex_integer (lexer);
+  lex_get (lexer);
+  
+  lex_match (lexer, ')');
+  return true;
+}
+
Index: merge/tests/automake.mk
===================================================================
--- merge.orig/tests/automake.mk        2007-06-04 21:46:10.000000000 -0700
+++ merge/tests/automake.mk     2007-06-04 21:52:06.000000000 -0700
@@ -8,6 +8,7 @@
        tests/command/beg-data.sh \
        tests/command/bignum.sh \
        tests/command/count.sh \
+       tests/command/datasheet.sh \
        tests/command/data-list.sh \
        tests/command/do-repeat.sh \
        tests/command/erase.sh \
Index: merge/tests/command/datasheet.sh
===================================================================
--- /dev/null   1970-01-01 00:00:00.000000000 +0000
+++ merge/tests/command/datasheet.sh    2007-06-04 21:52:06.000000000 -0700
@@ -0,0 +1,80 @@
+#!/bin/sh
+
+# This program tests datasheet support.
+
+TEMPDIR=/tmp/pspp-tst-$$
+TESTFILE=$TEMPDIR/`basename $0`.sps
+
+# ensure that top_builddir  are absolute
+if [ -z "$top_builddir" ] ; then top_builddir=. ; fi
+if [ -z "$top_srcdir" ] ; then top_srcdir=. ; fi
+top_builddir=`cd $top_builddir; pwd`
+PSPP=$top_builddir/src/ui/terminal/pspp
+
+# ensure that top_srcdir is absolute
+top_srcdir=`cd $top_srcdir; pwd`
+
+STAT_CONFIG_PATH=$top_srcdir/config
+export STAT_CONFIG_PATH
+
+LANG=C
+export LANG
+
+cleanup()
+{
+     cd /
+     rm -rf $TEMPDIR
+}
+
+
+fail()
+{
+    echo $activity
+    echo FAILED
+    cleanup;
+    exit 1;
+}
+
+
+no_result()
+{
+    echo $activity
+    echo NO RESULT;
+    cleanup;
+    exit 2;
+}
+
+pass()
+{
+    cleanup;
+    exit 0;
+}
+
+mkdir -p $TEMPDIR
+
+cd $TEMPDIR
+
+activity="Create File 1"
+cat > $TESTFILE <<EOF
+debug datasheet max=3,3 backing=0,0/progress=none/output=file("/dev/null").
+debug datasheet max=3,3 backing=3,3/progress=none/output=file("/dev/null").
+debug datasheet max=3,3 backing=3,1/progress=none/output=file("/dev/null").
+debug datasheet max=3,3 backing=1,3/progress=none/output=file("/dev/null").
+EOF
+if [ $? -ne 0 ] ; then no_result ; fi
+
+
+activity="Run pspp 1"
+$SUPERVISOR $PSPP --testing-mode $TESTFILE > datasheet.out
+if [ $? -ne 0 ] ; then no_result ; fi
+
+activity="compare results"
+diff -b  $TEMPDIR/datasheet.out - <<EOF
+Datasheet test max(3,3) backing(0,0) successful.
+Datasheet test max(3,3) backing(3,3) successful.
+Datasheet test max(3,3) backing(3,1) successful.
+Datasheet test max(3,3) backing(1,3) successful.
+EOF
+if [ $? -ne 0 ] ; then fail ; fi
+
+pass;

--





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