[PATCH] diffseq: don’t assume integers lack padding

[Paul Eggert]

* NEWS: Mention this.
* lib/diffseq.h (OFFSET_MAX): Don’t define;
this is now the user’s responsibility.
* lib/fstrcmp.c (OFFSET_MAX): Define to PTRDIFF_MAX.
---
 ChangeLog     | 8 ++++++++
 NEWS          | 2 ++
 lib/diffseq.h | 5 +----
 lib/fstrcmp.c | 1 +
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8e980741c5..426cc797be 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2023-05-19  Paul Eggert  <eggert@cs.ucla.edu>
+
+       diffseq: don’t assume integers lack padding
+       * NEWS: Mention this.
+       * lib/diffseq.h (OFFSET_MAX): Don’t define;
+       this is now the user’s responsibility.
+       * lib/fstrcmp.c (OFFSET_MAX): Define to PTRDIFF_MAX.
+
 2023-05-18  Bruno Haible  <bruno@clisp.org>
 
        getndelim2: Silence gcc warning.
diff --git a/NEWS b/NEWS
index 1457cb1413..8bc86311e9 100644
--- a/NEWS
+++ b/NEWS
@@ -74,6 +74,8 @@ User visible incompatible changes
 
 Date        Modules         Changes
 
+2023-05-19  diffseq         Includers should now also define OFFSET_MAX.
+
 2023-04-28  largefile-required
             year2038-required
                             Modules removed, for consistency with Autoconf
diff --git a/lib/diffseq.h b/lib/diffseq.h
index dfaf4f295e..ea45d9f892 100644
--- a/lib/diffseq.h
+++ b/lib/diffseq.h
@@ -48,6 +48,7 @@
      OFFSET                  A signed integer type sufficient to hold the
                              difference between two indices.  Usually
                              something like ptrdiff_t.
+     OFFSET_MAX              The maximum value of OFFSET (e.g., PTRDIFF_MAX).
      EXTRA_CONTEXT_FIELDS    Declarations of fields for 'struct context'.
      NOTE_DELETE(ctxt, xoff) Record the removal of the object xvec[xoff].
      NOTE_INSERT(ctxt, yoff) Record the insertion of the object yvec[yoff].
@@ -73,10 +74,6 @@
      #include "minmax.h"
  */
 
-/* Maximum value of type OFFSET.  */
-#define OFFSET_MAX \
-  ((((OFFSET)1 << (sizeof (OFFSET) * CHAR_BIT - 2)) - 1) * 2 + 1)
-
 /* Default to no early abort.  */
 #ifndef EARLY_ABORT
 # define EARLY_ABORT(ctxt) false
diff --git a/lib/fstrcmp.c b/lib/fstrcmp.c
index ab4cb03ed3..02f935a969 100644
--- a/lib/fstrcmp.c
+++ b/lib/fstrcmp.c
@@ -37,6 +37,7 @@
 #define ELEMENT char
 #define EQUAL(x,y) ((x) == (y))
 #define OFFSET ptrdiff_t
+#define OFFSET_MAX PTRDIFF_MAX
 #define EXTRA_CONTEXT_FIELDS \
   /* The number of edits beyond which the computation can be aborted. */ \
   ptrdiff_t edit_count_limit; \
-- 
2.39.2