contrib/diffutils-2.8/lib/cmpbuf.c

   1 /* Buffer primitives for comparison operations.
   2
   3    Copyright (C) 1993, 1995, 1998, 2001, 2002 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; see the file COPYING.
  17    If not, write to the Free Software Foundation,
  18    59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  19
  20 #if HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <errno.h>
  25 #include <limits.h>
  26
  27 #include <signal.h>
  28 #ifndef SA_RESTART
  29 # ifdef SA_INTERRUPT /* e.g. SunOS 4.1.x */
  30 #  define SA_RESTART SA_INTERRUPT
  31 # else
  32 #  define SA_RESTART 0
  33 # endif
  34 #endif
  35
  36 #if HAVE_UNISTD_H
  37 # include <unistd.h>
  38 #endif
  39
  40 #if HAVE_INTTYPES_H
  41 # include <inttypes.h>
  42 #endif
  43
  44 #include <sys/types.h>
  45 #include "cmpbuf.h"
  46
  47 /* Determine whether an integer type is signed, and its bounds.
  48    This code assumes two's (or one's!) complement with no holes.  */
  49
  50 /* The extra casts work around common compiler bugs,
  51    e.g. Cray C 5.0.3.0 when t == time_t.  */
  52 #ifndef TYPE_SIGNED
  53 # define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  54 #endif
  55 #ifndef TYPE_MINIMUM
  56 # define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  57                                ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) \
  58                                : (t) 0))
  59 #endif
  60 #ifndef TYPE_MAXIMUM
  61 # define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  62 #endif
  63
  64 #ifndef PTRDIFF_MAX
  65 # define PTRDIFF_MAX TYPE_MAXIMUM (ptrdiff_t)
  66 #endif
  67 #ifndef SIZE_MAX
  68 # define SIZE_MAX TYPE_MAXIMUM (size_t)
  69 #endif
  70 #ifndef SSIZE_MAX
  71 # define SSIZE_MAX TYPE_MAXIMUM (ssize_t)
  72 #endif
  73
  74 #undef MIN
  75 #define MIN(a, b) ((a) <= (b) ? (a) : (b))
  76
  77 /* Read NBYTES bytes from descriptor FD into BUF.
  78    NBYTES must not be SIZE_MAX.
  79    Return the number of characters successfully read.
  80    On error, return SIZE_MAX, setting errno.
  81    The number returned is always NBYTES unless end-of-file or error.  */
  82
  83 size_t
  84 block_read (int fd, char *buf, size_t nbytes)
  85 {
  86   char *bp = buf;
  87   char const *buflim = buf + nbytes;
  88   size_t readlim = SSIZE_MAX;
  89
  90   do
  91     {
  92       size_t bytes_to_read = MIN (buflim - bp, readlim);
  93       ssize_t nread = read (fd, bp, bytes_to_read);
  94       if (nread <= 0)
  95         {
  96           if (nread == 0)
  97             break;
  98
  99           /* Accommodate Tru64 5.1, which can't read more than INT_MAX
 100              bytes at a time.  They call that a 64-bit OS?  */
 101           if (errno == EINVAL && INT_MAX < bytes_to_read)
 102             {
 103               readlim = INT_MAX;
 104               continue;
 105             }
 106
 107           /* This is needed for programs that have signal handlers on
 108              older hosts without SA_RESTART.  It also accommodates
 109              ancient AIX hosts that set errno to EINTR after uncaught
 110              SIGCONT.  See <news:1r77ojINN85n@ftp.UU.NET>
 111              (1993-04-22).  */
 112           if (! SA_RESTART && errno == EINTR)
 113             continue;
 114
 115           return SIZE_MAX;
 116         }
 117       bp += nread;
 118     }
 119   while (bp < buflim);
 120
 121   return bp - buf;
 122 }
 123
 124 /* Least common multiple of two buffer sizes A and B.  However, if
 125    either A or B is zero, or if the multiple is greater than LCM_MAX,
 126    return a reasonable buffer size.  */
 127
 128 size_t
 129 buffer_lcm (size_t a, size_t b, size_t lcm_max)
 130 {
 131   size_t lcm, m, n, q, r;
 132
 133   /* Yield reasonable values if buffer sizes are zero.  */
 134   if (!a)
 135     return b ? b : 8 * 1024;
 136   if (!b)
 137     return a;
 138
 139   /* n = gcd (a, b) */
 140   for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
 141     continue;
 142
 143   /* Yield a if there is an overflow.  */
 144   q = a / n;
 145   lcm = q * b;
 146   return lcm <= lcm_max && lcm / b == q ? lcm : a;
 147 }