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new module finpending (was: Re: yesno module consumes too much input)


From: Bruno Haible
Subject: new module finpending (was: Re: yesno module consumes too much input)
Date: Sun, 19 Aug 2007 01:19:08 +0200
User-agent: KMail/1.5.4

Eric Blake wrote:
> m4 already calls close_stdin always, whether or not it read from stdin, so
> the current implementation is correct even when stdin is still in the
> initial state.  However, if you want to optimize it further, such patches
> are worth considering.

Here is a primitive function that could be used in close_stdin to optimize
away the lseek system call.

The function name 'finpending()' is not particularly good. Can you think of a
better name?

Tested on glibc, MacOS X, NetBSD, AIX, HP-UX, IRIX, Solaris, OSF/1, BeOS, mingw.

Comments?


2007-08-18  Bruno Haible  <address@hidden>

        * modules/finpending: New file.
        * lib/finpending.h: New file.
        * lib/finpending.c: New file.

============================= modules/finpending =============================
Description:
finpending() function: Determine the number of bytes waiting in the input
buffer of a stream.

Files:
lib/finpending.h
lib/finpending.c

Depends-on:

configure.ac:

Makefile.am:
lib_SOURCES += finpending.c

Include:
"finpending.h"

License:
LGPL

Maintainer:
Bruno Haible

============================== lib/finpending.h ==============================
/* Retrieve information about a FILE stream.
   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, 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 <stddef.h>
#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

/* Assuming the stream STREAM is open for reading:
   Return the number of bytes waiting in the input buffer of STREAM.

   If this number is 0 and the stream is not currently writing,
   fflush (STREAM) is known to be a no-op.

   STREAM must not be wide-character oriented.  */

extern size_t finpending (FILE *stream);

#ifdef __cplusplus
}
#endif
============================== lib/finpending.c ==============================
/* Retrieve information about a FILE stream.
   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, 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>

/* Specification.  */
#include "finpending.h"

size_t
finpending (FILE *fp)
{
#if defined _IO_ferror_unlocked     /* GNU libc, BeOS */
  if (fp->_IO_write_ptr > fp->_IO_write_base)
    return 0;
  return fp->_IO_read_end - fp->_IO_read_ptr;
#elif defined __sferror             /* FreeBSD, NetBSD, OpenBSD, MacOS X, 
Cygwin */
  if ((fp->_flags & __SWR) != 0 || fp->_r < 0)
    return 0;
  return fp->_r;
#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, mingw 
*/
# if defined __sun && defined __sparc && defined _LP64 /* Solaris/SPARC 64-bit 
*/
#  define fp_ ((struct { unsigned char *_ptr; \
                         unsigned char *_base; \
                         unsigned char *_end; \
                         long _cnt; \
                       } *) fp)
  if ((((unsigned int *) fp) [9] & _IOWRT) != 0)
    return 0;
  return fp_->_cnt;
# else
  if ((fp->_flag & _IOWRT) != 0)
    return 0;
  return fp->_cnt;
# endif
#elif defined __UCLIBC__            /* uClibc */
# ifdef __STDIO_BUFFERS
  if (fp->__modeflags & __FLAG_WRITING)
    return 0;
  return fp->__bufread - fp->__bufpos;
# else
  return 0;
# endif
#else
 #error "Please port gnulib finpending.c to your platform! Look at the 
definition of fflush, fread on your system, then report this to bug-gnulib."
#endif
}
==============================================================================





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