Wei Chang Shen
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Embedded Artists
Diff: png/crc32.c
- Revision:
- 2:0e2ef1edf01b
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/png/crc32.c Thu Jun 02 04:52:54 2016 +0000
@@ -0,0 +1,424 @@
+/* crc32.c -- compute the CRC-32 of a data stream
+ * 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 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>
+# ifndef DYNAMIC_CRC_TABLE
+# define DYNAMIC_CRC_TABLE
+# endif /* !DYNAMIC_CRC_TABLE */
+#endif /* MAKECRCH */
+
+#include "zutil.h" /* for STDC and FAR definitions */
+
+#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 */
+
+/* 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 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()
+{
+#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(crc, buf, len)
+ 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 *)(const void 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 *)(const void 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 */
+
+#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;
+}
+