/* Buffer primitives for comparison operations.

   Copyright (C) 1993, 1995, 1998, 2001-2002, 2006, 2009-2013, 2015-2017 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 3 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, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

#include <errno.h>

#include <limits.h>

#include <signal.h>

#include <unistd.h>

#include <stdint.h>

#include <inttypes.h>

#include <sys/types.h>

#include "cmpbuf.h"

#include "intprops.h"

#ifndef SSIZE_MAX

# define SSIZE_MAX TYPE_MAXIMUM (ssize_t)

#endif

#undef MIN

#define MIN(a, b) ((a) <= (b) ? (a) : (b))

/* Read NBYTES bytes from descriptor FD into BUF.

   NBYTES must not be SIZE_MAX.

   Return the number of characters successfully read.

   On error, return SIZE_MAX, setting errno.

   The number returned is always NBYTES unless end-of-file or error.  */

size_t

block_read (int fd, char *buf, size_t nbytes)

{

  char *bp = buf;

  char const *buflim = buf + nbytes;

  size_t readlim = MIN (SSIZE_MAX, SIZE_MAX);

  do

    {

      size_t bytes_remaining = buflim - bp;

      size_t bytes_to_read = MIN (bytes_remaining, readlim);

      ssize_t nread = read (fd, bp, bytes_to_read);

      if (nread <= 0)

	{

	  if (nread == 0)

	    break;

	  /* Accommodate Tru64 5.1, which can't read more than INT_MAX

	     bytes at a time.  They call that a 64-bit OS?  */

	  if (errno == EINVAL && INT_MAX < bytes_to_read)

	    {

	      readlim = INT_MAX;

	      continue;

	    }

	  /* This is needed for programs that have signal handlers on

	     older hosts without SA_RESTART.  It also accommodates

	     ancient AIX hosts that set errno to EINTR after uncaught

	     SIGCONT.  See <news:1r77ojINN85n@ftp.UU.NET>

	     (1993-04-22).  */

	  if (! SA_RESTART && errno == EINTR)

	    continue;

	  return SIZE_MAX;

	}

      bp += nread;

    }

  while (bp < buflim);

  return bp - buf;

}

/* Least common multiple of two buffer sizes A and B.  However, if

   either A or B is zero, or if the multiple is greater than LCM_MAX,

   return a reasonable buffer size.  */

size_t

buffer_lcm (size_t a, size_t b, size_t lcm_max)

{

  size_t lcm, m, n, q, r;

  /* Yield reasonable values if buffer sizes are zero.  */

  if (!a)

    return b ? b : 8 * 1024;

  if (!b)

    return a;

  /* n = gcd (a, b) */

  for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)

    continue;

  /* Yield a if there is an overflow.  */

  q = a / n;

  lcm = q * b;

  return lcm <= lcm_max && lcm / b == q ? lcm : a;

}