crc32.c

一个基于Zlib算法的

//* crc32.c -- compute the CRC-32 of a data stream
 * Copyright (C) 1995-2003 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */
#define _REScrc32h

#ifdef MAKECRCH
    #include <stdio.h>
    #ifndef DYNAMIC_CRC_TABLE
        #define DYNAMIC_CRC_TABLE
    #endif /* !DYNAMIC_CRC_TABLE */
#endif /* MAKECRCH */
/*#include "zutil.h" */     /* for STDC and FAR definitions */
#include "sdk/exlib/compress/zutil.h"
/*
#define local static
*/
/* Find a four-byte integer type for crc32_little() and crc32_big(). */
#ifndef NOBYFOUR
    #ifdef STDC           /* need ANSI C limits.h to determine sizes */
        #include <limits.h>
        #define BYFOUR
        #if (UINT_MAX == 0xffffffffUL)
            typedef unsigned int u4;
        #else
            #if (ULONG_MAX == 0xffffffffUL)
                typedef unsigned long u4;
            #else
                #if (USHRT_MAX == 0xffffffffUL)
                    typedef unsigned short u4;
                #else
                    #undef BYFOUR     /* can't find a four-byte integer type! */
                #endif
            #endif
        #endif
    #endif /* STDC */
#endif /* !NOBYFOUR */

/*##################################################################################
	define globle variable.
*/


/*##################################################################################
	declare funtions.
*/
/* Definitions for doing the crc four data bytes at a time. */
#ifdef BYFOUR
    #define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+(((w)&0xff00)<<8)+(((w)&0xff)<<24))
    static unsigned long crc32_little(unsigned long,const unsigned char FAR *, unsigned);
    static unsigned long crc32_big(unsigned long,const unsigned char FAR *, unsigned);
    #define TBLS 8
#else
    #define TBLS 1
#endif /* BYFOUR */

/*##################################################################################
	define functions.
*/

/*
  Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  protection on the static variables used to control the first-use generation
  of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  first call get_crc_table() to initialize the tables before allowing more than
  one thread to use crc32().
 */
#ifdef DYNAMIC_CRC_TABLE

    static volatile int crc_table_empty = 1;
    static unsigned long FAR crc_table[TBLS][256];
    static void make_crc_table(void);

    #ifdef MAKECRCH
       static void write_table(FILE *, const unsigned long FAR *);
    #endif /* MAKECRCH */

    /*
      Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
      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.

      Polynomials over GF(2) are represented in binary, one bit per coefficient,
      with the lowest powers in the most significant bit.  Then adding polynomials
      is just exclusive-or, and multiplying a polynomial by x is a right shift by
      one.  If we call the above polynomial p, and represent a byte as the
      polynomial q, also with the lowest power in the most significant bit (so the
      byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
      where a mod b means the remainder after dividing a by b.

      This calculation is done using the shift-register method of multiplying and
      taking the remainder.  The register is initialized to zero, and for each
      incoming bit, x^32 is added mod p to the register if the bit is a one (where
      x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
      x (which is shifting right by one and adding x^32 mod p if the bit shifted
      out is a one).  We start with the highest power (least significant bit) of
      q and repeat for all eight bits of q.

      The first table is simply the CRC of all possible eight bit values.  This is
      all the information needed to generate CRCs on data a byte at a time for all
      combinations of CRC register values and incoming bytes.  The remaining tables
      allow for word-at-a-time CRC calculation for both big-endian and little-
      endian machines, where a word is four bytes.
    */
    static void make_crc_table()
    {
        unsigned long c;
        int n, k;
        unsigned long poly;                 /* polynomial exclusive-or pattern */
        /* terms of polynomial defining this crc (except x^32): */
        static volatile int first = 1;      /* flag to limit concurrent making */
        static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

        /* See if another task is already doing this (not thread-safe, but better
           than nothing -- significantly reduces duration of vulnerability in
           case the advice about DYNAMIC_CRC_TABLE is ignored) */
        if (first) {
            first = 0;

            /* make exclusive-or pattern from polynomial (0xedb88320UL) */
            poly = 0UL;
            for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
                poly |= 1UL << (31 - p[n]);

            /* generate a crc for every 8-bit value */
            for (n = 0; n < 256; n++) {
                c = (unsigned long)n;
                for (k = 0; k < 8; k++)
                    c = c & 1 ? poly ^ (c >> 1) : c >> 1;
                crc_table[0][n] = c;
            }

    #ifdef BYFOUR
            /* generate crc for each value followed by one, two, and three zeros,
               and then the byte reversal of those as well as the first table */
            for (n = 0; n < 256; n++) {
                c = crc_table[0][n];
                crc_table[4][n] = REV(c);
                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);
                }
            }
    #endif /* BYFOUR */

            crc_table_empty = 0;
        }
        else {      /* not first */
            /* wait for the other guy to finish (not efficient, but rare) */
            while (crc_table_empty)
                ;
        }

    #ifdef MAKECRCH
        /* write out CRC tables to crc32.h */
        {
            FILE *out;

            out = fopen("crc32.h", "w");
            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, "static const unsigned long FAR ");
            fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
            write_table(out, crc_table[0]);
    #ifdef BYFOUR
            fprintf(out, "#ifdef BYFOUR\n");
            for (k = 1; k < 8; k++) {
                fprintf(out, "  },\n  {\n");
                write_table(out, crc_table[k]);
            }
            fprintf(out, "#endif\n");
    #endif /* BYFOUR */
            fprintf(out, "  }\n};\n");
            fclose(out);
        }
    #endif /* MAKECRCH */
    }

    #ifdef MAKECRCH
        static void write_table(FILE *, const unsigned long FAR *table)
        {
            int n;

            for (n = 0; n < 256; n++)
                fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
                        n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
        }
    #endif /* MAKECRCH */

#else /* !DYNAMIC_CRC_TABLE */
/* ========================================================================
 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 */
    #include "sdk/exlib/compress/crc32.h"

#endif /* DYNAMIC_CRC_TABLE */




/* =========================================================================
 * This function can be used by asm versions of crc32()
 */
const unsigned long FAR * ZEXPORT get_crc_table()
{
#ifdef DYNAMIC_CRC_TABLE
    if (crc_table_empty)
        make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
    return (const unsigned long FAR *)crc_table;
}

/* ========================================================================= */
#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1

/* ========================================================================= */
unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, unsigned len)
{
    if (buf == Z_NULL) return 0UL;

#ifdef DYNAMIC_CRC_TABLE
    if (crc_table_empty)
        make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */

#ifdef BYFOUR
    if (sizeof(void *) == sizeof(ptrdiff_t)) {
        u4 endian;

        endian = 1;
        if (*((unsigned char *)(&endian)))
            return crc32_little(crc, buf, len);
        else
            return crc32_big(crc, buf, len);
    }
#endif /* BYFOUR */
    crc = crc ^ 0xffffffffUL;
    while (len >= 8) {
        DO8;
        len -= 8;
    }
    if (len) do {
        DO1;
    } while (--len);
    return crc ^ 0xffffffffUL;
}

#ifdef BYFOUR

/* ========================================================================= */
#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]
#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4

/* ========================================================================= */
static unsigned long crc32_little(unsigned long crc, const unsigned char FAR *buf, unsigned len)
{
    register u4 c;
    register const u4 FAR *buf4;

    c = (u4)crc;
    c = ~c;
    while (len && ((ptrdiff_t)buf & 3)) {
        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
        len--;
    }

    buf4 = (const u4 FAR *)buf;
    while (len >= 32) {
        DOLIT32;
        len -= 32;
    }
    while (len >= 4) {
        DOLIT4;
        len -= 4;
    }
    buf = (const unsigned char FAR *)buf4;

    if (len) do {
        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
    } while (--len);
    c = ~c;
    return (unsigned long)c;
}

/* ========================================================================= */
#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]
#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4

/* ========================================================================= */
static unsigned long crc32_big(unsigned long crc, const unsigned char FAR *buf, unsigned len)
{
    register u4 c;
    register const u4 FAR *buf4;

    c = REV((u4)crc);
    c = ~c;
    while (len && ((ptrdiff_t)buf & 3)) {
        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
        len--;
    }

    buf4 = (const u4 FAR *)buf;
    buf4--;
    while (len >= 32) {
        DOBIG32;
        len -= 32;
    }
    while (len >= 4) {
        DOBIG4;
        len -= 4;
    }
    buf4++;
    buf = (const unsigned char FAR *)buf4;

    if (len) do {
        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
    } while (--len);
    c = ~c;
    return (unsigned long)(REV(c));
}

#endif /* BYFOUR */