contrib/diffutils/lib/cmpbuf.c

   1 /* Buffer primitives for comparison operations.
   2
   3    Copyright (C) 1993, 1995, 1998, 2001-2002, 2006, 2009-2013 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation, either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include <config.h>
  20
  21 #include <errno.h>
  22 #include <limits.h>
  23 #include <signal.h>
  24 #include <unistd.h>
  25 #include <stdint.h>
  26 #include <inttypes.h>
  27 #include <sys/types.h>
  28 #include "cmpbuf.h"
  29 #include "intprops.h"
  30
  31 #ifndef SSIZE_MAX
  32 # define SSIZE_MAX TYPE_MAXIMUM (ssize_t)
  33 #endif
  34
  35 #undef MIN
  36 #define MIN(a, b) ((a) <= (b) ? (a) : (b))
  37
  38 /* Read NBYTES bytes from descriptor FD into BUF.
  39    NBYTES must not be SIZE_MAX.
  40    Return the number of characters successfully read.
  41    On error, return SIZE_MAX, setting errno.
  42    The number returned is always NBYTES unless end-of-file or error.  */
  43
  44 size_t
  45 block_read (int fd, char *buf, size_t nbytes)
  46 {
  47   char *bp = buf;
  48   char const *buflim = buf + nbytes;
  49   size_t readlim = MIN (SSIZE_MAX, SIZE_MAX);
  50
  51   do
  52     {
  53       size_t bytes_remaining = buflim - bp;
  54       size_t bytes_to_read = MIN (bytes_remaining, readlim);
  55       ssize_t nread = read (fd, bp, bytes_to_read);
  56       if (nread <= 0)
  57         {
  58           if (nread == 0)
  59             break;
  60
  61           /* Accommodate Tru64 5.1, which can't read more than INT_MAX
  62              bytes at a time.  They call that a 64-bit OS?  */
  63           if (errno == EINVAL && INT_MAX < bytes_to_read)
  64             {
  65               readlim = INT_MAX;
  66               continue;
  67             }
  68
  69           /* This is needed for programs that have signal handlers on
  70              older hosts without SA_RESTART.  It also accommodates
  71              ancient AIX hosts that set errno to EINTR after uncaught
  72              SIGCONT.  See <news:1r77ojINN85n@ftp.UU.NET>
  73              (1993-04-22).  */
  74           if (! SA_RESTART && errno == EINTR)
  75             continue;
  76
  77           return SIZE_MAX;
  78         }
  79       bp += nread;
  80     }
  81   while (bp < buflim);
  82
  83   return bp - buf;
  84 }
  85
  86 /* Least common multiple of two buffer sizes A and B.  However, if
  87    either A or B is zero, or if the multiple is greater than LCM_MAX,
  88    return a reasonable buffer size.  */
  89
  90 size_t
  91 buffer_lcm (size_t a, size_t b, size_t lcm_max)
  92 {
  93   size_t lcm, m, n, q, r;
  94
  95   /* Yield reasonable values if buffer sizes are zero.  */
  96   if (!a)
  97     return b ? b : 8 * 1024;
  98   if (!b)
  99     return a;
 100
 101   /* n = gcd (a, b) */
 102   for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
 103     continue;
 104
 105   /* Yield a if there is an overflow.  */
 106   q = a / n;
 107   lcm = q * b;
 108   return lcm <= lcm_max && lcm / b == q ? lcm : a;
 109 }