root/tools/packfi2/crc32.c

DEFINITIONS

1. make_crc_table
2. write_table
3. get_crc_table
4. crc32
5. crc32_little
6. crc32_big
7. gf2_matrix_times
8. gf2_matrix_square
9. crc32_combine

   1 /* crc32.c -- compute the CRC-32 of a data stream

   2  * Copyright (C) 1995-2005 Mark Adler

   3  * For conditions of distribution and use, see copyright notice in zlib.h

   4  *

   5  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster

   6  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing

   7  * tables for updating the shift register in one step with three exclusive-ors

   8  * instead of four steps with four exclusive-ors.  This results in about a

   9  * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.

  10  */
  12 /* @(#) $Id$ */
  14 /*

  15   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore

  16   protection on the static variables used to control the first-use generation

  17   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should

  18   first call get_crc_table() to initialize the tables before allowing more than

  19   one thread to use crc32().

  20  */
  22 #ifdef MAKECRCH
  23 #  include <stdio.h>
  24 #  ifndef DYNAMIC_CRC_TABLE
  25 #    define DYNAMIC_CRC_TABLE
  26 #  endif /* !DYNAMIC_CRC_TABLE */
  27 #endif /* MAKECRCH */
  29 #include "zutil.h"      /* for STDC and FAR definitions */
  31 #define local static
  33 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
  34 #ifndef NOBYFOUR
  35 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
  36 #    include <limits.h>
  37 #    define BYFOUR
  38 #    if (UINT_MAX == 0xffffffffUL)
  39        typedef unsigned int u4;
  40 #    else
  41 #      if (ULONG_MAX == 0xffffffffUL)
  42          typedef unsigned long u4;
  43 #      else
  44 #        if (USHRT_MAX == 0xffffffffUL)
  45            typedef unsigned short u4;
  46 #        else
  47 #          undef BYFOUR     /* can't find a four-byte integer type! */
  48 #        endif
  49 #      endif
  50 #    endif
  51 #  endif /* STDC */
  52 #endif /* !NOBYFOUR */
  54 /* Definitions for doing the crc four data bytes at a time. */
  55 #ifdef BYFOUR
  56 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
  57                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
local unsigned long crc32_little OF((unsigned long,
  59                         const unsigned char FAR *, unsigned));
local unsigned long crc32_big OF((unsigned long,
  61                         const unsigned char FAR *, unsigned));
  62 #  define TBLS 8
  63 #else
  64 #  define TBLS 1
  65 #endif /* BYFOUR */
  67 /* Local functions for crc concatenation */
local unsigned long gf2_matrix_times OF((unsigned long *mat,
  69                                          unsigned long vec));
local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
  72 #ifdef DYNAMIC_CRC_TABLE
local volatile int crc_table_empty = 1;
local unsigned long FAR crc_table[TBLS][256];
local void make_crc_table OF((void));
  77 #ifdef MAKECRCH
local void write_table OF((FILE *, const unsigned long FAR *));
  79 #endif /* MAKECRCH */
  80 /*

  81   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:

  82   x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.

  83 

  84   Polynomials over GF(2) are represented in binary, one bit per coefficient,

  85   with the lowest powers in the most significant bit.  Then adding polynomials

  86   is just exclusive-or, and multiplying a polynomial by x is a right shift by

  87   one.  If we call the above polynomial p, and represent a byte as the

  88   polynomial q, also with the lowest power in the most significant bit (so the

  89   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,

  90   where a mod b means the remainder after dividing a by b.

  91 

  92   This calculation is done using the shift-register method of multiplying and

  93   taking the remainder.  The register is initialized to zero, and for each

  94   incoming bit, x^32 is added mod p to the register if the bit is a one (where

  95   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by

  96   x (which is shifting right by one and adding x^32 mod p if the bit shifted

  97   out is a one).  We start with the highest power (least significant bit) of

  98   q and repeat for all eight bits of q.

  99 

 100   The first table is simply the CRC of all possible eight bit values.  This is

 101   all the information needed to generate CRCs on data a byte at a time for all

 102   combinations of CRC register values and incoming bytes.  The remaining tables

 103   allow for word-at-a-time CRC calculation for both big-endian and little-

 104   endian machines, where a word is four bytes.

 105 */
local void make_crc_table()
 107 {
 108     unsigned long c;
 109     int n, k;
 110     unsigned long poly;                 /* polynomial exclusive-or pattern */
 111     /* terms of polynomial defining this crc (except x^32): */
 112     static volatile int first = 1;      /* flag to limit concurrent making */
 113     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
 115     /* See if another task is already doing this (not thread-safe, but better

 116        than nothing -- significantly reduces duration of vulnerability in

 117        case the advice about DYNAMIC_CRC_TABLE is ignored) */
 118     if (first) {
first = 0;
 121         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
poly = 0UL;
 123         for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
poly |= 1UL << (31 - p[n]);
 126         /* generate a crc for every 8-bit value */
 127         for (n = 0; n < 256; n++) {
c = (unsigned long)n;
 129             for (k = 0; k < 8; k++)
c = c & 1 ? poly ^ (c >> 1) : c >> 1;
crc_table[0][n] = c;
 132         }
 134 #ifdef BYFOUR
 135         /* generate crc for each value followed by one, two, and three zeros,

 136            and then the byte reversal of those as well as the first table */
 137         for (n = 0; n < 256; n++) {
c = crc_table[0][n];
crc_table[4][n] = REV(c);
 140             for (k = 1; k < 4; k++) {
c = crc_table[0][c & 0xff] ^ (c >> 8);
crc_table[k][n] = c;
crc_table[k + 4][n] = REV(c);
 144             }
 145         }
 146 #endif /* BYFOUR */
crc_table_empty = 0;
 149     }
 150     else {      /* not first */
 151         /* wait for the other guy to finish (not efficient, but rare) */
 152         while (crc_table_empty)
 153             ;
 154     }
 156 #ifdef MAKECRCH
 157     /* write out CRC tables to crc32.h */
 158     {
FILE *out;
out = fopen("crc32.h", "w");
 162         if (out == NULL) return;
fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
fprintf(out, "local const unsigned long FAR ");
fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
write_table(out, crc_table[0]);
 168 #  ifdef BYFOUR
fprintf(out, "#ifdef BYFOUR\n");
 170         for (k = 1; k < 8; k++) {
fprintf(out, "  },\n  {\n");
write_table(out, crc_table[k]);
 173         }
fprintf(out, "#endif\n");
 175 #  endif /* BYFOUR */
fprintf(out, "  }\n};\n");
fclose(out);
 178     }
 179 #endif /* MAKECRCH */
 180 }
 182 #ifdef MAKECRCH
local void write_table(out, table)
FILE *out;
 185     const unsigned long FAR *table;
 186 {
 187     int n;
 189     for (n = 0; n < 256; n++)
fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
 192 }
 193 #endif /* MAKECRCH */
 195 #else /* !DYNAMIC_CRC_TABLE */
 196 /* ========================================================================

 197  * Tables of CRC-32s of all single-byte values, made by make_crc_table().

 198  */
 199 #include "crc32.h"
 200 #endif /* DYNAMIC_CRC_TABLE */
 202 /* =========================================================================

 203  * This function can be used by asm versions of crc32()

 204  */
 205 const unsigned long FAR * ZEXPORT get_crc_table()
 206 {
 207 #ifdef DYNAMIC_CRC_TABLE
 208     if (crc_table_empty)
make_crc_table();
 210 #endif /* DYNAMIC_CRC_TABLE */
 211     return (const unsigned long FAR *)crc_table;
 212 }
 214 /* ========================================================================= */
 215 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
 216 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
 218 /* ========================================================================= */
 219 unsigned long ZEXPORT crc32(crc, buf, len)
 220     unsigned long crc;
 221     const unsigned char FAR *buf;
 222     unsigned len;
 223 {
 224     if (buf == Z_NULL) return 0UL;
 226 #ifdef DYNAMIC_CRC_TABLE
 227     if (crc_table_empty)
make_crc_table();
 229 #endif /* DYNAMIC_CRC_TABLE */
 231 #ifdef BYFOUR
 232     if (sizeof(void *) == sizeof(ptrdiff_t)) {
u4 endian;
endian = 1;
 236         if (*((unsigned char *)(&endian)))
 237             return crc32_little(crc, buf, len);
 238         else
 239             return crc32_big(crc, buf, len);
 240     }
 241 #endif /* BYFOUR */
crc = crc ^ 0xffffffffUL;
 243     while (len >= 8) {
DO8;
len -= 8;
 246     }
 247     if (len) do {
DO1;
 249     } while (--len);
 250     return crc ^ 0xffffffffUL;
 251 }
 253 #ifdef BYFOUR
 255 /* ========================================================================= */
 256 #define DOLIT4 c ^= *buf4++; \
c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
 259 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
 261 /* ========================================================================= */
local unsigned long crc32_little(crc, buf, len)
 263     unsigned long crc;
 264     const unsigned char FAR *buf;
 265     unsigned len;
 266 {
 267     register u4 c;
 268     register const u4 FAR *buf4;
c = (u4)crc;
c = ~c;
 272     while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
len--;
 275     }
buf4 = (const u4 FAR *)(const void FAR *)buf;
 278     while (len >= 32) {
DOLIT32;
len -= 32;
 281     }
 282     while (len >= 4) {
DOLIT4;
len -= 4;
 285     }
buf = (const unsigned char FAR *)buf4;
 288     if (len) do {
c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 290     } while (--len);
c = ~c;
 292     return (unsigned long)c;
 293 }
 295 /* ========================================================================= */
 296 #define DOBIG4 c ^= *++buf4; \
c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 299 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
 301 /* ========================================================================= */
local unsigned long crc32_big(crc, buf, len)
 303     unsigned long crc;
 304     const unsigned char FAR *buf;
 305     unsigned len;
 306 {
 307     register u4 c;
 308     register const u4 FAR *buf4;
c = REV((u4)crc);
c = ~c;
 312     while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
len--;
 315     }
buf4 = (const u4 FAR *)(const void FAR *)buf;
buf4--;
 319     while (len >= 32) {
DOBIG32;
len -= 32;
 322     }
 323     while (len >= 4) {
DOBIG4;
len -= 4;
 326     }
buf4++;
buf = (const unsigned char FAR *)buf4;
 330     if (len) do {
c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 332     } while (--len);
c = ~c;
 334     return (unsigned long)(REV(c));
 335 }
 337 #endif /* BYFOUR */
 339 #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
 341 /* ========================================================================= */
local unsigned long gf2_matrix_times(mat, vec)
 343     unsigned long *mat;
 344     unsigned long vec;
 345 {
 346     unsigned long sum;
sum = 0;
 349     while (vec) {
 350         if (vec & 1)
sum ^= *mat;
vec >>= 1;
mat++;
 354     }
 355     return sum;
 356 }
 358 /* ========================================================================= */
local void gf2_matrix_square(square, mat)
 360     unsigned long *square;
 361     unsigned long *mat;
 362 {
 363     int n;
 365     for (n = 0; n < GF2_DIM; n++)
square[n] = gf2_matrix_times(mat, mat[n]);
 367 }
 369 /* ========================================================================= */
uLong ZEXPORT crc32_combine(crc1, crc2, len2)
uLong crc1;
uLong crc2;
z_off_t len2;
 374 {
 375     int n;
 376     unsigned long row;
 377     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
 378     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
 380     /* degenerate case */
 381     if (len2 == 0)
 382         return crc1;
 384     /* put operator for one zero bit in odd */
odd[0] = 0xedb88320L;           /* CRC-32 polynomial */
row = 1;
 387     for (n = 1; n < GF2_DIM; n++) {
odd[n] = row;
row <<= 1;
 390     }
 392     /* put operator for two zero bits in even */
gf2_matrix_square(even, odd);
 395     /* put operator for four zero bits in odd */
gf2_matrix_square(odd, even);
 398     /* apply len2 zeros to crc1 (first square will put the operator for one

 399        zero byte, eight zero bits, in even) */
 400     do {
 401         /* apply zeros operator for this bit of len2 */
gf2_matrix_square(even, odd);
 403         if (len2 & 1)
crc1 = gf2_matrix_times(even, crc1);
len2 >>= 1;
 407         /* if no more bits set, then done */
 408         if (len2 == 0)
 409             break;
 411         /* another iteration of the loop with odd and even swapped */
gf2_matrix_square(odd, even);
 413         if (len2 & 1)
crc1 = gf2_matrix_times(odd, crc1);
len2 >>= 1;
 417         /* if no more bits set, then done */
 418     } while (len2 != 0);
 420     /* return combined crc */
crc1 ^= crc2;
 422     return crc1;
 423 }