gnu/dist/diffutils/lib/cmpbuf.c

   1 /*      $NetBSD$        */
   2
   3 /* Buffer primitives for comparison operations.
   4
   5    Copyright (C) 1993, 1995, 1998, 2001, 2002 Free Software Foundation, Inc.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2, or (at your option)
  10    any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; see the file COPYING.
  19    If not, write to the Free Software Foundation,
  20    59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  21
  22 #if HAVE_CONFIG_H
  23 # include <config.h>
  24 #endif
  25
  26 #include <errno.h>
  27 #include <limits.h>
  28
  29 #include <signal.h>
  30 #ifndef SA_RESTART
  31 # ifdef SA_INTERRUPT /* e.g. SunOS 4.1.x */
  32 #  define SA_RESTART SA_INTERRUPT
  33 # else
  34 #  define SA_RESTART 0
  35 # endif
  36 #endif
  37
  38 #if HAVE_UNISTD_H
  39 # include <unistd.h>
  40 #endif
  41
  42 #if HAVE_INTTYPES_H
  43 # include <inttypes.h>
  44 #endif
  45
  46 #include <sys/types.h>
  47 #include "cmpbuf.h"
  48
  49 /* Determine whether an integer type is signed, and its bounds.
  50    This code assumes two's (or one's!) complement with no holes.  */
  51
  52 /* The extra casts work around common compiler bugs,
  53    e.g. Cray C 5.0.3.0 when t == time_t.  */
  54 #ifndef TYPE_SIGNED
  55 # define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  56 #endif
  57 #ifndef TYPE_MINIMUM
  58 # define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  59                                ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) \
  60                                : (t) 0))
  61 #endif
  62 #ifndef TYPE_MAXIMUM
  63 # define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  64 #endif
  65
  66 #ifndef PTRDIFF_MAX
  67 # define PTRDIFF_MAX TYPE_MAXIMUM (ptrdiff_t)
  68 #endif
  69 #ifndef SIZE_MAX
  70 # define SIZE_MAX TYPE_MAXIMUM (size_t)
  71 #endif
  72 #ifndef SSIZE_MAX
  73 # define SSIZE_MAX TYPE_MAXIMUM (ssize_t)
  74 #endif
  75
  76 #undef MIN
  77 #define MIN(a, b) ((a) <= (b) ? (a) : (b))
  78
  79 /* Read NBYTES bytes from descriptor FD into BUF.
  80    NBYTES must not be SIZE_MAX.
  81    Return the number of characters successfully read.
  82    On error, return SIZE_MAX, setting errno.
  83    The number returned is always NBYTES unless end-of-file or error.  */
  84
  85 size_t
  86 block_read (int fd, char *buf, size_t nbytes)
  87 {
  88   char *bp = buf;
  89   char const *buflim = buf + nbytes;
  90   size_t readlim = SSIZE_MAX;
  91
  92   do
  93     {
  94       size_t bytes_to_read = MIN (buflim - bp, readlim);
  95       ssize_t nread = read (fd, bp, bytes_to_read);
  96       if (nread <= 0)
  97         {
  98           if (nread == 0)
  99             break;
 100
 101           /* Accommodate Tru64 5.1, which can't read more than INT_MAX
 102              bytes at a time.  They call that a 64-bit OS?  */
 103           if (errno == EINVAL && INT_MAX < bytes_to_read)
 104             {
 105               readlim = INT_MAX;
 106               continue;
 107             }
 108
 109           /* This is needed for programs that have signal handlers on
 110              older hosts without SA_RESTART.  It also accommodates
 111              ancient AIX hosts that set errno to EINTR after uncaught
 112              SIGCONT.  See <news:1r77ojINN85n@ftp.UU.NET>
 113              (1993-04-22).  */
 114           if (! SA_RESTART && errno == EINTR)
 115             continue;
 116
 117           return SIZE_MAX;
 118         }
 119       bp += nread;
 120     }
 121   while (bp < buflim);
 122
 123   return bp - buf;
 124 }
 125
 126 /* Least common multiple of two buffer sizes A and B.  However, if
 127    either A or B is zero, or if the multiple is greater than LCM_MAX,
 128    return a reasonable buffer size.  */
 129
 130 size_t
 131 buffer_lcm (size_t a, size_t b, size_t lcm_max)
 132 {
 133   size_t lcm, m, n, q, r;
 134
 135   /* Yield reasonable values if buffer sizes are zero.  */
 136   if (!a)
 137     return b ? b : 8 * 1024;
 138   if (!b)
 139     return a;
 140
 141   /* n = gcd (a, b) */
 142   for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
 143     continue;
 144
 145   /* Yield a if there is an overflow.  */
 146   q = a / n;
 147   lcm = q * b;
 148   return lcm <= lcm_max && lcm / b == q ? lcm : a;
 149 }