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| -rw-r--r-- | crc32.c | 360 |
1 files changed, 360 insertions, 0 deletions
@@ -0,0 +1,360 @@ +/* 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 + * + * Note: zlib license from from zlib.h added explicitly as mdadm does + * not include zlib.h. License from v1.2.2 of zlib: + * + * This software is provided 'as-is', without any express or implied + * warranty. In no event will the authors be held liable for any damages + * arising from the use of this software. + * + * Permission is granted to anyone to use this software for any purpose, + * including commercial applications, and to alter it and redistribute it + * freely, subject to the following restrictions: + * + * 1. The origin of this software must not be misrepresented; you must not + * claim that you wrote the original software. If you use this software + * in a product, an acknowledgment in the product documentation would be + * appreciated but is not required. + * 2. Altered source versions must be plainly marked as such, and must not be + * misrepresented as being the original software. + * 3. This notice may not be removed or altered from any source distribution. + * + * + * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster + * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing + * tables for updating the shift register in one step with three exclusive-ors + * instead of four steps with four exclusive-ors. This results about a factor + * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. + */ + +/* @(#) $Id$ */ + +/* + 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 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 */ +#define STDC +#define FAR +#define Z_NULL ((void*)0) +#define OF(X) X +#define ZEXPORT +typedef long ptrdiff_t; +#define NOBYFOUR + +#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 */ + +/* 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)) + local unsigned long crc32_little OF((unsigned long, + const unsigned char FAR *, unsigned)); + local unsigned long crc32_big OF((unsigned long, + const unsigned char FAR *, unsigned)); +# define TBLS 8 +#else +# define TBLS 1 +#endif /* BYFOUR */ + +#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)); +#ifdef MAKECRCH + local void write_table OF((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. +*/ +local 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, "local 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 +local void write_table(out, table) + FILE *out; + 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 "crc32.h" +#endif /* DYNAMIC_CRC_TABLE */ + +/* ========================================================================= + * This function can be used by asm versions of crc32() + */ +const unsigned long FAR * ZEXPORT get_crc_table(void) +{ +#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 + +/* ========================================================================= */ +local unsigned long crc32_little(crc, buf, len) + 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 + +/* ========================================================================= */ +local unsigned long crc32_big(crc, buf, len) + 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 */ |