root/lib/libz/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 /*      $OpenBSD: crc32.c,v 1.11 2005/07/20 15:56:45 millert Exp $      */
    2 /* crc32.c -- compute the CRC-32 of a data stream
    3  * Copyright (C) 1995-2005 Mark Adler
    4  * For conditions of distribution and use, see copyright notice in zlib.h
    5  *
    6  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
    7  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
    8  * tables for updating the shift register in one step with three exclusive-ors
    9  * instead of four steps with four exclusive-ors.  This results in about a
   10  * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
   11  */
   13 /*
   14   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
   15   protection on the static variables used to control the first-use generation
   16   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
   17   first call get_crc_table() to initialize the tables before allowing more than
   18   one thread to use crc32().
   19  */
   21 #ifdef MAKECRCH
   22 #  include <stdio.h>
   23 #  ifndef DYNAMIC_CRC_TABLE
   24 #    define DYNAMIC_CRC_TABLE
   25 #  endif /* !DYNAMIC_CRC_TABLE */
   26 #endif /* MAKECRCH */
   28 #include "zutil.h"      /* for STDC and FAR definitions */
   30 #define local static
   32 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
   33 #ifndef NOBYFOUR
   34 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
   35 #    include <limits.h>
   36 #    define BYFOUR
   37 #    if (UINT_MAX == 0xffffffffUL)
   38        typedef unsigned int u4;
   39 #    else
   40 #      if (ULONG_MAX == 0xffffffffUL)
   41          typedef unsigned long u4;
   42 #      else
   43 #        if (USHRT_MAX == 0xffffffffUL)
   44            typedef unsigned short u4;
   45 #        else
   46 #          undef BYFOUR     /* can't find a four-byte integer type! */
   47 #        endif
   48 #      endif
   49 #    endif
   50 #  endif /* STDC */
   51 #endif /* !NOBYFOUR */
   53 /* Definitions for doing the crc four data bytes at a time. */
   54 #ifdef BYFOUR
   55 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
   56                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
local unsigned long crc32_little OF((unsigned long,
   58                         const unsigned char FAR *, unsigned));
local unsigned long crc32_big OF((unsigned long,
   60                         const unsigned char FAR *, unsigned));
   61 #  define TBLS 8
   62 #else
   63 #  define TBLS 1
   64 #endif /* BYFOUR */
   66 /* Local functions for crc concatenation */
local unsigned long gf2_matrix_times OF((unsigned long *mat,
   68                                          unsigned long vec));
local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
   71 #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));
   76 #ifdef MAKECRCH
local void write_table OF((FILE *, const unsigned long FAR *));
   78 #endif /* MAKECRCH */
   79 /*
   80   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
   81   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.
   82 
   83   Polynomials over GF(2) are represented in binary, one bit per coefficient,
   84   with the lowest powers in the most significant bit.  Then adding polynomials
   85   is just exclusive-or, and multiplying a polynomial by x is a right shift by
   86   one.  If we call the above polynomial p, and represent a byte as the
   87   polynomial q, also with the lowest power in the most significant bit (so the
   88   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
   89   where a mod b means the remainder after dividing a by b.
   90 
   91   This calculation is done using the shift-register method of multiplying and
   92   taking the remainder.  The register is initialized to zero, and for each
   93   incoming bit, x^32 is added mod p to the register if the bit is a one (where
   94   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
   95   x (which is shifting right by one and adding x^32 mod p if the bit shifted
   96   out is a one).  We start with the highest power (least significant bit) of
   97   q and repeat for all eight bits of q.
   98 
   99   The first table is simply the CRC of all possible eight bit values.  This is
  100   all the information needed to generate CRCs on data a byte at a time for all
  101   combinations of CRC register values and incoming bytes.  The remaining tables
  102   allow for word-at-a-time CRC calculation for both big-endian and little-
  103   endian machines, where a word is four bytes.
  104 */
local void make_crc_table()
  106 {
  107     unsigned long c;
  108     int n, k;
  109     unsigned long poly;                 /* polynomial exclusive-or pattern */
  110     /* terms of polynomial defining this crc (except x^32): */
  111     static volatile int first = 1;      /* flag to limit concurrent making */
  112     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
  114     /* See if another task is already doing this (not thread-safe, but better
  115        than nothing -- significantly reduces duration of vulnerability in
  116        case the advice about DYNAMIC_CRC_TABLE is ignored) */
  117     if (first) {
first = 0;
  120         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
poly = 0UL;
  122         for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
poly |= 1UL << (31 - p[n]);
  125         /* generate a crc for every 8-bit value */
  126         for (n = 0; n < 256; n++) {
c = (unsigned long)n;
  128             for (k = 0; k < 8; k++)
c = c & 1 ? poly ^ (c >> 1) : c >> 1;
crc_table[0][n] = c;
  131         }
  133 #ifdef BYFOUR
  134         /* generate crc for each value followed by one, two, and three zeros,
  135            and then the byte reversal of those as well as the first table */
  136         for (n = 0; n < 256; n++) {
c = crc_table[0][n];
crc_table[4][n] = REV(c);
  139             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);
  143             }
  144         }
  145 #endif /* BYFOUR */
crc_table_empty = 0;
  148     }
  149     else {      /* not first */
  150         /* wait for the other guy to finish (not efficient, but rare) */
  151         while (crc_table_empty)
  152             ;
  153     }
  155 #ifdef MAKECRCH
  156     /* write out CRC tables to crc32.h */
  157     {
FILE *out;
out = fopen("crc32.h", "w");
  161         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]);
  167 #  ifdef BYFOUR
fprintf(out, "#ifdef BYFOUR\n");
  169         for (k = 1; k < 8; k++) {
fprintf(out, "  },\n  {\n");
write_table(out, crc_table[k]);
  172         }
fprintf(out, "#endif\n");
  174 #  endif /* BYFOUR */
fprintf(out, "  }\n};\n");
fclose(out);
  177     }
  178 #endif /* MAKECRCH */
  179 }
  181 #ifdef MAKECRCH
local void write_table(out, table)
FILE *out;
  184     const unsigned long FAR *table;
  185 {
  186     int n;
  188     for (n = 0; n < 256; n++)
fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
  191 }
  192 #endif /* MAKECRCH */
  194 #else /* !DYNAMIC_CRC_TABLE */
  195 /* ========================================================================
  196  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
  197  */
  198 #include "crc32.h"
  199 #endif /* DYNAMIC_CRC_TABLE */
  201 /* =========================================================================
  202  * This function can be used by asm versions of crc32()
  203  */
  204 const unsigned long FAR * ZEXPORT get_crc_table()
  205 {
  206 #ifdef DYNAMIC_CRC_TABLE
  207     if (crc_table_empty)
make_crc_table();
  209 #endif /* DYNAMIC_CRC_TABLE */
  210     return (const unsigned long FAR *)crc_table;
  211 }
  213 /* ========================================================================= */
  214 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
  215 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
  217 /* ========================================================================= */
  218 unsigned long ZEXPORT crc32(crc, buf, len)
  219     unsigned long crc;
  220     const unsigned char FAR *buf;
  221     unsigned len;
  222 {
  223     if (buf == Z_NULL) return 0UL;
  225 #ifdef DYNAMIC_CRC_TABLE
  226     if (crc_table_empty)
make_crc_table();
  228 #endif /* DYNAMIC_CRC_TABLE */
  230 #ifdef BYFOUR
  231     if (sizeof(void *) == sizeof(ptrdiff_t)) {
u4 endian;
endian = 1;
  235         if (*((unsigned char *)(&endian)))
  236             return crc32_little(crc, buf, len);
  237         else
  238             return crc32_big(crc, buf, len);
  239     }
  240 #endif /* BYFOUR */
crc = crc ^ 0xffffffffUL;
  242     while (len >= 8) {
DO8;
len -= 8;
  245     }
  246     if (len) do {
DO1;
  248     } while (--len);
  249     return crc ^ 0xffffffffUL;
  250 }
  252 #ifdef BYFOUR
  254 /* ========================================================================= */
  255 #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]
  258 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
  260 /* ========================================================================= */
local unsigned long crc32_little(crc, buf, len)
  262     unsigned long crc;
  263     const unsigned char FAR *buf;
  264     unsigned len;
  265 {
  266     register u4 c;
  267     register const u4 FAR *buf4;
c = (u4)crc;
c = ~c;
  271     while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
len--;
  274     }
buf4 = (const u4 FAR *)(const void FAR *)buf;
  277     while (len >= 32) {
DOLIT32;
len -= 32;
  280     }
  281     while (len >= 4) {
DOLIT4;
len -= 4;
  284     }
buf = (const unsigned char FAR *)buf4;
  287     if (len) do {
c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
  289     } while (--len);
c = ~c;
  291     return (unsigned long)c;
  292 }
  294 /* ========================================================================= */
  295 #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]
  298 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
  300 /* ========================================================================= */
local unsigned long crc32_big(crc, buf, len)
  302     unsigned long crc;
  303     const unsigned char FAR *buf;
  304     unsigned len;
  305 {
  306     register u4 c;
  307     register const u4 FAR *buf4;
c = REV((u4)crc);
c = ~c;
  311     while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
len--;
  314     }
buf4 = (const u4 FAR *)(const void FAR *)buf;
buf4--;
  318     while (len >= 32) {
DOBIG32;
len -= 32;
  321     }
  322     while (len >= 4) {
DOBIG4;
len -= 4;
  325     }
buf4++;
buf = (const unsigned char FAR *)buf4;
  329     if (len) do {
c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
  331     } while (--len);
c = ~c;
  333     return (unsigned long)(REV(c));
  334 }
  336 #endif /* BYFOUR */
  338 #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
  340 /* ========================================================================= */
local unsigned long gf2_matrix_times(mat, vec)
  342     unsigned long *mat;
  343     unsigned long vec;
  344 {
  345     unsigned long sum;
sum = 0;
  348     while (vec) {
  349         if (vec & 1)
sum ^= *mat;
vec >>= 1;
mat++;
  353     }
  354     return sum;
  355 }
  357 /* ========================================================================= */
local void gf2_matrix_square(square, mat)
  359     unsigned long *square;
  360     unsigned long *mat;
  361 {
  362     int n;
  364     for (n = 0; n < GF2_DIM; n++)
square[n] = gf2_matrix_times(mat, mat[n]);
  366 }
  368 /* ========================================================================= */
uLong ZEXPORT crc32_combine(crc1, crc2, len2)
uLong crc1;
uLong crc2;
z_off_t len2;
  373 {
  374     int n;
  375     unsigned long row;
  376     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
  377     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
  379     /* degenerate case */
  380     if (len2 == 0)
  381         return crc1;
  383     /* put operator for one zero bit in odd */
odd[0] = 0xedb88320L;           /* CRC-32 polynomial */
row = 1;
  386     for (n = 1; n < GF2_DIM; n++) {
odd[n] = row;
row <<= 1;
  389     }
  391     /* put operator for two zero bits in even */
gf2_matrix_square(even, odd);
  394     /* put operator for four zero bits in odd */
gf2_matrix_square(odd, even);
  397     /* apply len2 zeros to crc1 (first square will put the operator for one
  398        zero byte, eight zero bits, in even) */
  399     do {
  400         /* apply zeros operator for this bit of len2 */
gf2_matrix_square(even, odd);
  402         if (len2 & 1)
crc1 = gf2_matrix_times(even, crc1);
len2 >>= 1;
  406         /* if no more bits set, then done */
  407         if (len2 == 0)
  408             break;
  410         /* another iteration of the loop with odd and even swapped */
gf2_matrix_square(odd, even);
  412         if (len2 & 1)
crc1 = gf2_matrix_times(odd, crc1);
len2 >>= 1;
  416         /* if no more bits set, then done */
  417     } while (len2 != 0);
  419     /* return combined crc */
crc1 ^= crc2;
  421     return crc1;
  422 }