/* crc32.c -- compute the CRC-32 of a data stream
- * Copyright (C) 1995-2003 Mark Adler
+ * Copyright (C) 1995-2005 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.
+ * 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.
*/
-/* @(#) $Id$ */
+
+/*
+ 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>
# define TBLS 1
#endif /* BYFOUR */
+/* 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));
+
#ifdef DYNAMIC_CRC_TABLE
-local int crc_table_empty = 1;
+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.
{
unsigned long c;
int n, k;
- unsigned long poly; /* polynomial exclusive-or pattern */
+ 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};
- /* 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;
- }
+ /* 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);
+ /* 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;
+ 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 */
const unsigned long FAR * ZEXPORT get_crc_table()
{
#ifdef DYNAMIC_CRC_TABLE
- if (crc_table_empty) make_crc_table();
+ if (crc_table_empty)
+ make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
- return (const unsigned long FAR *)crc_table;
+ return (const unsigned long FAR *)crc_table;
}
/* ========================================================================= */
len--;
}
- buf4 = (const u4 FAR *)buf;
+ buf4 = (const u4 FAR *)(const void FAR *)buf;
while (len >= 32) {
DOLIT32;
len -= 32;
len--;
}
- buf4 = (const u4 FAR *)buf;
+ buf4 = (const u4 FAR *)(const void FAR *)buf;
buf4--;
while (len >= 32) {
DOBIG32;
}
#endif /* BYFOUR */
+
+#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]);
+}
+
+/* ========================================================================= */
+uLong ZEXPORT crc32_combine(crc1, crc2, len2)
+ uLong crc1;
+ uLong crc2;
+ z_off_t len2;
+{
+ 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 */
+
+ /* degenerate case */
+ if (len2 == 0)
+ return crc1;
+
+ /* put operator for one zero bit in odd */
+ odd[0] = 0xedb88320L; /* CRC-32 polynomial */
+ 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;
+}
projects / wxWidgets.git / blobdiff