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1/* crctab.c -- supply the CRC table needed for CRC-32 calculations.
2 * Copyright (C) 1995 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6/* $Id$ */
7
8/*
9 Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
10 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.
11
12 Polynomials over GF(2) are represented in binary, one bit per coefficient,
13 with the lowest powers in the most significant bit. Then adding polynomials
14 is just exclusive-or, and multiplying a polynomial by x is a right shift by
15 one. If we call the above polynomial p, and represent a byte as the
16 polynomial q, also with the lowest power in the most significant bit (so the
17 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
18 where a mod b means the remainder after dividing a by b.
19
20 This calculation is done using the shift-register method of multiplying and
21 taking the remainder. The register is initialized to zero, and for each
22 incoming bit, x^32 is added mod p to the register if the bit is a one (where
23 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
24 x (which is shifting right by one and adding x^32 mod p if the bit shifted
25 out is a one). We start with the highest power (least significant bit) of
26 q and repeat for all eight bits of q.
27
28 The table is simply the CRC of all possible eight bit values. This is all
29 the information needed to generate CRC's on data a byte at a time for all
30 combinations of CRC register values and incoming bytes.
31*/
32
33#define __CRCTAB_C /* identifies this source module */
34
35#include "zip.h"
36
37#if (!defined(USE_ZLIB) || defined(USE_OWN_CRCTAB))
38
39#ifndef ZCONST
40# define ZCONST const
41#endif
42
43#ifdef DYNAMIC_CRC_TABLE
44
45/* =========================================================================
46 * Make the crc table. This function is needed only if you want to compute
47 * the table dynamically.
48 */
49
50local void make_crc_table OF((void));
51
52#if (defined(DYNALLOC_CRCTAB) && defined(REENTRANT))
53 error: Dynamic allocation of CRC table not safe with reentrant code.
54#endif /* DYNALLOC_CRCTAB && REENTRANT */
55
56#ifdef DYNALLOC_CRCTAB
57 local ulg near *crc_table = NULL;
58# if 0 /* not used, since sizeof("near *") <= sizeof(int) */
59 /* Use this section when access to a "local int" is faster than access to
60 a "local pointer" (e.g.: i86 16bit code with far pointers). */
61 local int crc_table_empty = 1;
62# define CRC_TABLE_IS_EMPTY (crc_table_empty != 0)
63# define MARK_CRCTAB_FILLED crc_table_empty = 0
64# define MARK_CRCTAB_EMPTY crc_table_empty = 1
65# else
66 /* Use this section on systems where the size of pointers and ints is
67 equal (e.g.: all 32bit systems). */
68# define CRC_TABLE_IS_EMPTY (crc_table == NULL)
69# define MARK_CRCTAB_FILLED crc_table = crctab_p
70# define MARK_CRCTAB_EMPTY crc_table = NULL
71# endif
72#else /* !DYNALLOC_CRCTAB */
73 local ulg near crc_table[256];
74 local int crc_table_empty = 1;
75# define CRC_TABLE_IS_EMPTY (crc_table_empty != 0)
76# define MARK_CRCTAB_FILLED crc_table_empty = 0
77#endif /* ?DYNALLOC_CRCTAB */
78
79
80local void make_crc_table()
81{
82 ulg c; /* crc shift register */
83 int n; /* counter for all possible eight bit values */
84 int k; /* byte being shifted into crc apparatus */
85#ifdef DYNALLOC_CRCTAB
86 ulg near *crctab_p; /* temporary pointer to allocated crc_table area */
87#else /* !DYNALLOC_CRCTAB */
88# define crctab_p crc_table
89#endif /* DYNALLOC_CRCTAB */
90
91#ifdef COMPUTE_XOR_PATTERN
92 /* This piece of code has been left here to explain how the XOR pattern
93 * used in the creation of the crc_table values can be recomputed.
94 * For production versions of this function, it is more efficient to
95 * supply the resultant pattern at compile time.
96 */
97 ulg xor; /* polynomial exclusive-or pattern */
98 /* terms of polynomial defining this crc (except x^32): */
99 static uch p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
100
101 /* make exclusive-or pattern from polynomial (0xedb88320L) */
102 xor = 0L;
103 for (i = 0; i < sizeof(p)/sizeof(uch); i++)
104 xor |= 1L << (31 - p[i]);
105#else
106# define xor 0xedb88320L
107#endif
108
109#ifdef DYNALLOC_CRCTAB
110 crctab_p = (ulg near *) nearmalloc (256*sizeof(ulg));
111 if (crctab_p == NULL) {
112 ziperr(ZE_MEM, "crc_table allocation");
113 }
114#endif /* DYNALLOC_CRCTAB */
115
116 for (n = 0; n < 256; n++) {
117 c = (ulg)n;
118 for (k = 8; k; k--)
119 c = c & 1 ? xor ^ (c >> 1) : c >> 1;
120 crctab_p[n] = c;
121 }
122 MARK_CRCTAB_FILLED;
123}
124
125#else /* !DYNAMIC_CRC_TABLE */
126
127#ifdef DYNALLOC_CRCTAB
128 error: Inconsistent flags, DYNALLOC_CRCTAB without DYNAMIC_CRC_TABLE.
129#endif
130
131/* ========================================================================
132 * Table of CRC-32's of all single-byte values (made by make_crc_table)
133 */
134local ZCONST ulg near crc_table[256] = {
135 0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
136 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
137 0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
138 0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
139 0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
140 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
141 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
142 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
143 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
144 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
145 0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
146 0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
147 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
148 0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
149 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
150 0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
151 0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
152 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
153 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
154 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
155 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
156 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
157 0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
158 0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
159 0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
160 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
161 0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
162 0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
163 0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
164 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
165 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
166 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
167 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
168 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
169 0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
170 0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
171 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
172 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
173 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
174 0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
175 0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
176 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
177 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
178 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
179 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
180 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
181 0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
182 0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
183 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
184 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
185 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
186 0x2d02ef8dL
187};
188#endif /* ?DYNAMIC_CRC_TABLE */
189
190/* use "OF((void))" here to work around a Borland TC++ 1.0 problem */
191#ifdef USE_ZLIB
192ZCONST uLongf *get_crc_table OF((void))
193#else
194ZCONST ulg near *get_crc_table OF((void))
195#endif
196{
197#ifdef DYNAMIC_CRC_TABLE
198 if (CRC_TABLE_IS_EMPTY)
199 make_crc_table();
200#endif
201#ifdef USE_ZLIB
202 return (ZCONST uLongf *)crc_table;
203#else
204 return (ZCONST ulg near *)crc_table;
205#endif
206}
207
208#ifdef DYNALLOC_CRCTAB
209void free_crc_table()
210{
211 if (!CRC_TABLE_IS_EMPTY)
212 {
213 nearfree((ulg near *)crc_table);
214 MARK_CRCTAB_EMPTY;
215 }
216}
217#endif
218
219#endif /* !USE_ZLIB || USE_OWN_CRCTAB */