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/* crc32.c -- compute the CRC-32 of a data stream |
| 2 |
* Copyright (C) 1995-2006, 2010, 2011, 2012 Mark Adler |
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* For conditions of distribution and use, see copyright notice in zlib.h |
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* |
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* Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster |
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* CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing |
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* tables for updating the shift register in one step with three exclusive-ors |
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* instead of four steps with four exclusive-ors. This results in about a |
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* factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. |
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*/ |
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|
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/* @(#) $Id$ */ |
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|
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/* |
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Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore |
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protection on the static variables used to control the first-use generation |
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of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should |
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first call get_crc_table() to initialize the tables before allowing more than |
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one thread to use crc32(). |
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|
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DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h. |
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*/ |
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|
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#ifdef MAKECRCH |
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# include <stdio.h> |
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# ifndef DYNAMIC_CRC_TABLE |
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# define DYNAMIC_CRC_TABLE |
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# endif /* !DYNAMIC_CRC_TABLE */ |
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#endif /* MAKECRCH */ |
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|
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#include "zutil.h" /* for STDC and FAR definitions */ |
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|
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#define local static |
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|
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/* Definitions for doing the crc four data bytes at a time. */ |
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#if !defined(NOBYFOUR) && defined(Z_U4) |
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# define BYFOUR |
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#endif |
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#ifdef BYFOUR |
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local unsigned long crc32_little OF((unsigned long, |
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const unsigned char FAR *, unsigned)); |
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local unsigned long crc32_big OF((unsigned long, |
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const unsigned char FAR *, unsigned)); |
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# define TBLS 8 |
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#else |
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# define TBLS 1 |
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#endif /* BYFOUR */ |
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|
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/* Local functions for crc concatenation */ |
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local unsigned long gf2_matrix_times OF((unsigned long *mat, |
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unsigned long vec)); |
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local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); |
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local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2)); |
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|
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|
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#ifdef DYNAMIC_CRC_TABLE |
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|
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local volatile int crc_table_empty = 1; |
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local z_crc_t FAR crc_table[TBLS][256]; |
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local void make_crc_table OF((void)); |
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#ifdef MAKECRCH |
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local void write_table OF((FILE *, const z_crc_t FAR *)); |
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#endif /* MAKECRCH */ |
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/* |
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Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: |
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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. |
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|
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Polynomials over GF(2) are represented in binary, one bit per coefficient, |
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with the lowest powers in the most significant bit. Then adding polynomials |
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is just exclusive-or, and multiplying a polynomial by x is a right shift by |
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one. If we call the above polynomial p, and represent a byte as the |
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polynomial q, also with the lowest power in the most significant bit (so the |
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byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
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where a mod b means the remainder after dividing a by b. |
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|
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This calculation is done using the shift-register method of multiplying and |
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taking the remainder. The register is initialized to zero, and for each |
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incoming bit, x^32 is added mod p to the register if the bit is a one (where |
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x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
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x (which is shifting right by one and adding x^32 mod p if the bit shifted |
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out is a one). We start with the highest power (least significant bit) of |
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q and repeat for all eight bits of q. |
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|
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The first table is simply the CRC of all possible eight bit values. This is |
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all the information needed to generate CRCs on data a byte at a time for all |
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combinations of CRC register values and incoming bytes. The remaining tables |
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allow for word-at-a-time CRC calculation for both big-endian and little- |
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endian machines, where a word is four bytes. |
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*/ |
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local void make_crc_table() |
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{ |
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z_crc_t c; |
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int n, k; |
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z_crc_t poly; /* polynomial exclusive-or pattern */ |
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/* terms of polynomial defining this crc (except x^32): */ |
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static volatile int first = 1; /* flag to limit concurrent making */ |
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static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
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|
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/* See if another task is already doing this (not thread-safe, but better |
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than nothing -- significantly reduces duration of vulnerability in |
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case the advice about DYNAMIC_CRC_TABLE is ignored) */ |
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if (first) { |
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first = 0; |
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|
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/* make exclusive-or pattern from polynomial (0xedb88320UL) */ |
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poly = 0; |
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for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++) |
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poly |= (z_crc_t)1 << (31 - p[n]); |
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|
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/* generate a crc for every 8-bit value */ |
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for (n = 0; n < 256; n++) { |
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c = (z_crc_t)n; |
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for (k = 0; k < 8; k++) |
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c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
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crc_table[0][n] = c; |
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} |
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|
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#ifdef BYFOUR |
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/* generate crc for each value followed by one, two, and three zeros, |
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and then the byte reversal of those as well as the first table */ |
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for (n = 0; n < 256; n++) { |
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c = crc_table[0][n]; |
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crc_table[4][n] = ZSWAP32(c); |
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for (k = 1; k < 4; k++) { |
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c = crc_table[0][c & 0xff] ^ (c >> 8); |
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crc_table[k][n] = c; |
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crc_table[k + 4][n] = ZSWAP32(c); |
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} |
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} |
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#endif /* BYFOUR */ |
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|
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crc_table_empty = 0; |
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} |
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else { /* not first */ |
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/* wait for the other guy to finish (not efficient, but rare) */ |
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while (crc_table_empty) |
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; |
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} |
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|
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#ifdef MAKECRCH |
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/* write out CRC tables to crc32.h */ |
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{ |
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FILE *out; |
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|
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out = fopen("crc32.h", "w"); |
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if (out == NULL) return; |
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fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); |
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fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); |
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fprintf(out, "local const z_crc_t FAR "); |
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fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); |
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write_table(out, crc_table[0]); |
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# ifdef BYFOUR |
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fprintf(out, "#ifdef BYFOUR\n"); |
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for (k = 1; k < 8; k++) { |
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fprintf(out, " },\n {\n"); |
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write_table(out, crc_table[k]); |
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} |
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fprintf(out, "#endif\n"); |
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# endif /* BYFOUR */ |
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fprintf(out, " }\n};\n"); |
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fclose(out); |
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} |
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#endif /* MAKECRCH */ |
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} |
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|
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#ifdef MAKECRCH |
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local void write_table(out, table) |
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FILE *out; |
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const z_crc_t FAR *table; |
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{ |
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int n; |
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|
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for (n = 0; n < 256; n++) |
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fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", |
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(unsigned long)(table[n]), |
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n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); |
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} |
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#endif /* MAKECRCH */ |
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|
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#else /* !DYNAMIC_CRC_TABLE */ |
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/* ======================================================================== |
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* Tables of CRC-32s of all single-byte values, made by make_crc_table(). |
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*/ |
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#include "crc32.h" |
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#endif /* DYNAMIC_CRC_TABLE */ |
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|
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/* ========================================================================= |
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* This function can be used by asm versions of crc32() |
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*/ |
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const z_crc_t FAR * ZEXPORT get_crc_table() |
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{ |
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#ifdef DYNAMIC_CRC_TABLE |
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if (crc_table_empty) |
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make_crc_table(); |
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#endif /* DYNAMIC_CRC_TABLE */ |
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return (const z_crc_t FAR *)crc_table; |
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} |
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|
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/* ========================================================================= */ |
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#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) |
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#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 |
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|
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/* ========================================================================= */ |
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unsigned long ZEXPORT crc32(crc, buf, len) |
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unsigned long crc; |
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const unsigned char FAR *buf; |
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uInt len; |
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{ |
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if (buf == Z_NULL) return 0UL; |
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|
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#ifdef DYNAMIC_CRC_TABLE |
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if (crc_table_empty) |
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make_crc_table(); |
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#endif /* DYNAMIC_CRC_TABLE */ |
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|
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#ifdef BYFOUR |
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if (sizeof(void *) == sizeof(ptrdiff_t)) { |
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z_crc_t endian; |
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|
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endian = 1; |
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if (*((unsigned char *)(&endian))) |
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return crc32_little(crc, buf, len); |
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else |
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return crc32_big(crc, buf, len); |
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} |
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#endif /* BYFOUR */ |
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crc = crc ^ 0xffffffffUL; |
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while (len >= 8) { |
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DO8; |
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len -= 8; |
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} |
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if (len) do { |
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DO1; |
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} while (--len); |
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return crc ^ 0xffffffffUL; |
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} |
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|
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#ifdef BYFOUR |
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|
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/* ========================================================================= */ |
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#define DOLIT4 c ^= *buf4++; \ |
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c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ |
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crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] |
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#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 |
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|
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/* ========================================================================= */ |
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local unsigned long crc32_little(crc, buf, len) |
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unsigned long crc; |
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const unsigned char FAR *buf; |
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unsigned len; |
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{ |
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register z_crc_t c; |
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register const z_crc_t FAR *buf4; |
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|
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c = (z_crc_t)crc; |
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c = ~c; |
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while (len && ((ptrdiff_t)buf & 3)) { |
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c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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len--; |
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} |
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|
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buf4 = (const z_crc_t FAR *)(const void FAR *)buf; |
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while (len >= 32) { |
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DOLIT32; |
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len -= 32; |
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} |
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while (len >= 4) { |
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DOLIT4; |
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len -= 4; |
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} |
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buf = (const unsigned char FAR *)buf4; |
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|
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if (len) do { |
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c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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} while (--len); |
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c = ~c; |
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return (unsigned long)c; |
| 278 |
} |
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|
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/* ========================================================================= */ |
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#define DOBIG4 c ^= *++buf4; \ |
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c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ |
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crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] |
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#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 |
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|
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/* ========================================================================= */ |
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local unsigned long crc32_big(crc, buf, len) |
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unsigned long crc; |
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const unsigned char FAR *buf; |
| 290 |
unsigned len; |
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{ |
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register z_crc_t c; |
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register const z_crc_t FAR *buf4; |
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|
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c = ZSWAP32((z_crc_t)crc); |
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c = ~c; |
| 297 |
while (len && ((ptrdiff_t)buf & 3)) { |
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c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
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len--; |
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} |
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|
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buf4 = (const z_crc_t FAR *)(const void FAR *)buf; |
| 303 |
buf4--; |
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while (len >= 32) { |
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DOBIG32; |
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len -= 32; |
| 307 |
} |
| 308 |
while (len >= 4) { |
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DOBIG4; |
| 310 |
len -= 4; |
| 311 |
} |
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buf4++; |
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buf = (const unsigned char FAR *)buf4; |
| 314 |
|
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if (len) do { |
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c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
| 317 |
} while (--len); |
| 318 |
c = ~c; |
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return (unsigned long)(ZSWAP32(c)); |
| 320 |
} |
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|
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#endif /* BYFOUR */ |
| 323 |
|
| 324 |
#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ |
| 325 |
|
| 326 |
/* ========================================================================= */ |
| 327 |
local unsigned long gf2_matrix_times(mat, vec) |
| 328 |
unsigned long *mat; |
| 329 |
unsigned long vec; |
| 330 |
{ |
| 331 |
unsigned long sum; |
| 332 |
|
| 333 |
sum = 0; |
| 334 |
while (vec) { |
| 335 |
if (vec & 1) |
| 336 |
sum ^= *mat; |
| 337 |
vec >>= 1; |
| 338 |
mat++; |
| 339 |
} |
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return sum; |
| 341 |
} |
| 342 |
|
| 343 |
/* ========================================================================= */ |
| 344 |
local void gf2_matrix_square(square, mat) |
| 345 |
unsigned long *square; |
| 346 |
unsigned long *mat; |
| 347 |
{ |
| 348 |
int n; |
| 349 |
|
| 350 |
for (n = 0; n < GF2_DIM; n++) |
| 351 |
square[n] = gf2_matrix_times(mat, mat[n]); |
| 352 |
} |
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|
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/* ========================================================================= */ |
| 355 |
local uLong crc32_combine_(crc1, crc2, len2) |
| 356 |
uLong crc1; |
| 357 |
uLong crc2; |
| 358 |
z_off64_t len2; |
| 359 |
{ |
| 360 |
int n; |
| 361 |
unsigned long row; |
| 362 |
unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ |
| 363 |
unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ |
| 364 |
|
| 365 |
/* degenerate case (also disallow negative lengths) */ |
| 366 |
if (len2 <= 0) |
| 367 |
return crc1; |
| 368 |
|
| 369 |
/* put operator for one zero bit in odd */ |
| 370 |
odd[0] = 0xedb88320UL; /* CRC-32 polynomial */ |
| 371 |
row = 1; |
| 372 |
for (n = 1; n < GF2_DIM; n++) { |
| 373 |
odd[n] = row; |
| 374 |
row <<= 1; |
| 375 |
} |
| 376 |
|
| 377 |
/* put operator for two zero bits in even */ |
| 378 |
gf2_matrix_square(even, odd); |
| 379 |
|
| 380 |
/* put operator for four zero bits in odd */ |
| 381 |
gf2_matrix_square(odd, even); |
| 382 |
|
| 383 |
/* apply len2 zeros to crc1 (first square will put the operator for one |
| 384 |
zero byte, eight zero bits, in even) */ |
| 385 |
do { |
| 386 |
/* apply zeros operator for this bit of len2 */ |
| 387 |
gf2_matrix_square(even, odd); |
| 388 |
if (len2 & 1) |
| 389 |
crc1 = gf2_matrix_times(even, crc1); |
| 390 |
len2 >>= 1; |
| 391 |
|
| 392 |
/* if no more bits set, then done */ |
| 393 |
if (len2 == 0) |
| 394 |
break; |
| 395 |
|
| 396 |
/* another iteration of the loop with odd and even swapped */ |
| 397 |
gf2_matrix_square(odd, even); |
| 398 |
if (len2 & 1) |
| 399 |
crc1 = gf2_matrix_times(odd, crc1); |
| 400 |
len2 >>= 1; |
| 401 |
|
| 402 |
/* if no more bits set, then done */ |
| 403 |
} while (len2 != 0); |
| 404 |
|
| 405 |
/* return combined crc */ |
| 406 |
crc1 ^= crc2; |
| 407 |
return crc1; |
| 408 |
} |
| 409 |
|
| 410 |
/* ========================================================================= */ |
| 411 |
uLong ZEXPORT crc32_combine(crc1, crc2, len2) |
| 412 |
uLong crc1; |
| 413 |
uLong crc2; |
| 414 |
z_off_t len2; |
| 415 |
{ |
| 416 |
return crc32_combine_(crc1, crc2, len2); |
| 417 |
} |
| 418 |
|
| 419 |
uLong ZEXPORT crc32_combine64(crc1, crc2, len2) |
| 420 |
uLong crc1; |
| 421 |
uLong crc2; |
| 422 |
z_off64_t len2; |
| 423 |
{ |
| 424 |
return crc32_combine_(crc1, crc2, len2); |
| 425 |
} |
