utils/Install/sfxzip/crc32.c

   1 /* crc32.c -- compute the CRC-32 of a data stream
   2  * Copyright (C) 1995 Mark Adler
   3  * For conditions of distribution and use, see copyright notice in zlib.h
   4  */
   5
   6 /* $Id$ */
   7
   8 #define __CRC32_C       /* identifies this source module */
   9
  10 #include "zip.h"
  11
  12 #ifndef USE_ZLIB
  13 #ifndef ASM_CRC
  14
  15 #ifndef ZCONST
  16 #  define ZCONST const
  17 #endif
  18
  19 #ifdef CRC32
  20 #  undef CRC32
  21 #endif
  22 #define CRC32(c, b) (crc_table[((int)(c) ^ (b)) & 0xff] ^ ((c) >> 8))
  23 #define DO1(buf)  crc = CRC32(crc, *buf++)
  24 #define DO2(buf)  DO1(buf); DO1(buf)
  25 #define DO4(buf)  DO2(buf); DO2(buf)
  26 #define DO8(buf)  DO4(buf); DO4(buf)
  27
  28 /* ========================================================================= */
  29 ulg crc32(crc, buf, len)
  30     register ulg crc;           /* crc shift register */
  31     register ZCONST uch *buf;   /* pointer to bytes to pump through */
  32     extent len;                 /* number of bytes in buf[] */
  33 /* Run a set of bytes through the crc shift register.  If buf is a NULL
  34    pointer, then initialize the crc shift register contents instead.
  35    Return the current crc in either case. */
  36 {
  37   register ZCONST ulg near *crc_table;
  38
  39   if (buf == NULL) return 0L;
  40
  41   crc_table = get_crc_table();
  42
  43   crc = crc ^ 0xffffffffL;
  44 #ifndef NO_UNROLLED_LOOPS
  45   while (len >= 8) {
  46     DO8(buf);
  47     len -= 8;
  48   }
  49 #endif
  50   if (len) do {
  51     DO1(buf);
  52   } while (--len);
  53   return crc ^ 0xffffffffL;     /* (instead of ~c for 64-bit machines) */
  54 }
  55 #endif /* !ASM_CRC */
  56 #endif /* !USE_ZLIB */