freebsd-dev/lib/libz/crc32.c

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/* crc32.c -- compute the CRC-32 of a data stream
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* 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
*
* 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
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* instead of four steps with four exclusive-ors. This results in about a
* factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
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*/
/* @(#) $Id$ */
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/*
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().
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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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#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 */
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#define local static
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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)
# define BYFOUR
#endif
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#ifdef BYFOUR
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 */
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/* Local functions for crc concatenation */
local unsigned long gf2_matrix_times OF((unsigned long *mat,
unsigned long vec));
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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#ifdef DYNAMIC_CRC_TABLE
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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.
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.
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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.
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*/
local void make_crc_table()
{
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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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/* 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) */
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poly = 0;
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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/* generate a crc for every 8-bit value */
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++)
c = c & 1 ? poly ^ (c >> 1) : c >> 1;
crc_table[0][n] = c;
}
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#ifdef BYFOUR
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/* 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];
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crc_table[4][n] = ZSWAP32(c);
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for (k = 1; k < 4; k++) {
c = crc_table[0][c & 0xff] ^ (c >> 8);
crc_table[k][n] = c;
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crc_table[k + 4][n] = ZSWAP32(c);
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}
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}
#endif /* BYFOUR */
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crc_table_empty = 0;
}
else { /* not first */
/* wait for the other guy to finish (not efficient, but rare) */
while (crc_table_empty)
;
}
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#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");
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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");
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 */
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}
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#ifdef MAKECRCH
local void write_table(out, table)
FILE *out;
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const z_crc_t FAR *table;
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{
int n;
for (n = 0; n < 256; n++)
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fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
(unsigned long)(table[n]),
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n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
}
#endif /* MAKECRCH */
#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"
#endif /* DYNAMIC_CRC_TABLE */
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/* =========================================================================
* This function can be used by asm versions of crc32()
*/
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const z_crc_t FAR * ZEXPORT get_crc_table()
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{
#ifdef DYNAMIC_CRC_TABLE
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if (crc_table_empty)
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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#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
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/* ========================================================================= */
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unsigned long ZEXPORT crc32(crc, buf, len)
unsigned long crc;
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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#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
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make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
#ifdef BYFOUR
if (sizeof(void *) == sizeof(ptrdiff_t)) {
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z_crc_t endian;
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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;
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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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#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;
{
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register z_crc_t c;
register const z_crc_t FAR *buf4;
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c = (z_crc_t)crc;
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c = ~c;
while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
len--;
}
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buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
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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;
{
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register z_crc_t c;
register const z_crc_t FAR *buf4;
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c = ZSWAP32((z_crc_t)crc);
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c = ~c;
while (len && ((ptrdiff_t)buf & 3)) {
c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
len--;
}
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buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
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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;
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return (unsigned long)(ZSWAP32(c));
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}
#endif /* BYFOUR */
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#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
/* ========================================================================= */
local unsigned long gf2_matrix_times(mat, vec)
unsigned long *mat;
unsigned long vec;
{
unsigned long sum;
sum = 0;
while (vec) {
if (vec & 1)
sum ^= *mat;
vec >>= 1;
mat++;
}
return sum;
}
/* ========================================================================= */
local void gf2_matrix_square(square, mat)
unsigned long *square;
unsigned long *mat;
{
int n;
for (n = 0; n < GF2_DIM; n++)
square[n] = gf2_matrix_times(mat, mat[n]);
}
/* ========================================================================= */
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local uLong crc32_combine_(crc1, crc2, len2)
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uLong crc1;
uLong crc2;
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z_off64_t len2;
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{
int n;
unsigned long row;
unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
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/* degenerate case (also disallow negative lengths) */
if (len2 <= 0)
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return crc1;
/* put operator for one zero bit in odd */
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odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
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row = 1;
for (n = 1; n < GF2_DIM; n++) {
odd[n] = row;
row <<= 1;
}
/* put operator for two zero bits in even */
gf2_matrix_square(even, odd);
/* put operator for four zero bits in odd */
gf2_matrix_square(odd, even);
/* apply len2 zeros to crc1 (first square will put the operator for one
zero byte, eight zero bits, in even) */
do {
/* apply zeros operator for this bit of len2 */
gf2_matrix_square(even, odd);
if (len2 & 1)
crc1 = gf2_matrix_times(even, crc1);
len2 >>= 1;
/* if no more bits set, then done */
if (len2 == 0)
break;
/* another iteration of the loop with odd and even swapped */
gf2_matrix_square(odd, even);
if (len2 & 1)
crc1 = gf2_matrix_times(odd, crc1);
len2 >>= 1;
/* if no more bits set, then done */
} while (len2 != 0);
/* return combined crc */
crc1 ^= crc2;
return crc1;
}
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/* ========================================================================= */
uLong ZEXPORT crc32_combine(crc1, crc2, len2)
uLong crc1;
uLong crc2;
z_off_t len2;
{
return crc32_combine_(crc1, crc2, len2);
}
uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
uLong crc1;
uLong crc2;
z_off64_t len2;
{
return crc32_combine_(crc1, crc2, len2);
}