freebsd-dev/lib/libz/crc32.c

313 lines
9.5 KiB
C
Raw Normal View History

1996-08-18 17:54:27 +00:00
/* crc32.c -- compute the CRC-32 of a data stream
2004-06-30 23:54:46 +00:00
* Copyright (C) 1995-2003 Mark Adler
* 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
* 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.
1996-08-18 17:54:27 +00:00
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
1996-08-18 17:54:27 +00:00
2004-06-30 23:54:46 +00:00
#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 */
1996-08-18 17:54:27 +00:00
#define local static
2004-06-30 23:54:46 +00:00
/* 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 */
1996-08-18 17:54:27 +00:00
#ifdef DYNAMIC_CRC_TABLE
local int crc_table_empty = 1;
2004-06-30 23:54:46 +00:00
local unsigned long FAR crc_table[TBLS][256];
1996-08-18 17:54:27 +00:00
local void make_crc_table OF((void));
2004-06-30 23:54:46 +00:00
#ifdef MAKECRCH
local void write_table OF((FILE *, const unsigned long FAR *));
#endif /* MAKECRCH */
1996-08-18 17:54:27 +00:00
/*
2004-06-30 23:54:46 +00:00
Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
1996-08-18 17:54:27 +00:00
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.
2004-06-30 23:54:46 +00:00
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.
1996-08-18 17:54:27 +00:00
*/
local void make_crc_table()
{
2004-06-30 23:54:46 +00:00
unsigned long c;
int n, k;
unsigned long poly; /* polynomial exclusive-or pattern */
/* terms of polynomial defining this crc (except x^32): */
static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
/* 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 */
1996-08-18 17:54:27 +00:00
crc_table_empty = 0;
2004-06-30 23:54:46 +00:00
#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 */
1996-08-18 17:54:27 +00:00
}
2004-06-30 23:54:46 +00:00
#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 */
1996-08-18 17:54:27 +00:00
/* ========================================================================
2004-06-30 23:54:46 +00:00
* Tables of CRC-32s of all single-byte values, made by make_crc_table().
1996-08-18 17:54:27 +00:00
*/
2004-06-30 23:54:46 +00:00
#include "crc32.h"
#endif /* DYNAMIC_CRC_TABLE */
1996-08-18 17:54:27 +00:00
/* =========================================================================
* This function can be used by asm versions of crc32()
*/
2004-06-30 23:54:46 +00:00
const unsigned long FAR * ZEXPORT get_crc_table()
1996-08-18 17:54:27 +00:00
{
#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty) make_crc_table();
2004-06-30 23:54:46 +00:00
#endif /* DYNAMIC_CRC_TABLE */
return (const unsigned long FAR *)crc_table;
1996-08-18 17:54:27 +00:00
}
/* ========================================================================= */
2004-06-30 23:54:46 +00:00
#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
1996-08-18 17:54:27 +00:00
/* ========================================================================= */
2004-06-30 23:54:46 +00:00
unsigned long ZEXPORT crc32(crc, buf, len)
unsigned long crc;
const unsigned char FAR *buf;
unsigned len;
1996-08-18 17:54:27 +00:00
{
2004-06-30 23:54:46 +00:00
if (buf == Z_NULL) return 0UL;
1996-08-18 17:54:27 +00:00
#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
2004-06-30 23:54:46 +00:00
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;
1996-08-18 17:54:27 +00:00
}
if (len) do {
2004-06-30 23:54:46 +00:00
DO1;
1996-08-18 17:54:27 +00:00
} while (--len);
2004-06-30 23:54:46 +00:00
return crc ^ 0xffffffffUL;
1996-08-18 17:54:27 +00:00
}
2004-06-30 23:54:46 +00:00
#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 */