1 /* crc32.c -- compute the CRC-32 of a data stream
2  * Copyright (C) 1995-2003 Mark Adler
3  * For conditions of distribution and use, see copyright notice in zlib.h
4  *
5  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
6  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
7  * tables for updating the shift register in one step with three exclusive-ors
8  * instead of four steps with four exclusive-ors.  This results about a factor
9  * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
10  */
11 
12 /* @(#) $Id$ */
13 
14 #ifdef MAKECRCH
15 #  include <stdio.h>
16 #  ifndef DYNAMIC_CRC_TABLE
17 #    define DYNAMIC_CRC_TABLE
18 #  endif /* !DYNAMIC_CRC_TABLE */
19 #endif /* MAKECRCH */
20 
21 #define local static
22 #define STDC
23 #define FAR
24 #define ZEXPORT
25 #define Z_NULL 0
26 #define OF(args) args
27 #include "crc32.h"
28 
29 #ifndef _WIN32
30 #define ptrdiff_t long
31 #else
32 #include <stdlib.h>
33 #endif
34 
35 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
36 #ifndef NOBYFOUR
37 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
38 #    include <limits.h>
39 #    define BYFOUR
40 #    if (UINT_MAX == 0xffffffffUL)
41        typedef unsigned int u4;
42 #    else
43 #      if (ULONG_MAX == 0xffffffffUL)
44          typedef unsigned long u4;
45 #      else
46 #        if (USHRT_MAX == 0xffffffffUL)
47            typedef unsigned short u4;
48 #        else
49 #          undef BYFOUR     /* can't find a four-byte integer type! */
50 #        endif
51 #      endif
52 #    endif
53 #  endif /* STDC */
54 #endif /* !NOBYFOUR */
55 
56 /* Definitions for doing the crc four data bytes at a time. */
57 #ifdef BYFOUR
58 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
59                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
60    local unsigned long crc32_little OF((unsigned long,
61                         const unsigned char FAR *, unsigned));
62    local unsigned long crc32_big OF((unsigned long,
63                         const unsigned char FAR *, unsigned));
64 #  define TBLS 8
65 #else
66 #  define TBLS 1
67 #endif /* BYFOUR */
68 
69 #ifdef DYNAMIC_CRC_TABLE
70 
71 local int crc_table_empty = 1;
72 local unsigned long FAR crc_table[TBLS][256];
73 local void make_crc_table OF((void));
74 #ifdef MAKECRCH
75    local void write_table OF((FILE *, const unsigned long FAR *));
76 #endif /* MAKECRCH */
77 
78 /*
79   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
80   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.
81 
82   Polynomials over GF(2) are represented in binary, one bit per coefficient,
83   with the lowest powers in the most significant bit.  Then adding polynomials
84   is just exclusive-or, and multiplying a polynomial by x is a right shift by
85   one.  If we call the above polynomial p, and represent a byte as the
86   polynomial q, also with the lowest power in the most significant bit (so the
87   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
88   where a mod b means the remainder after dividing a by b.
89 
90   This calculation is done using the shift-register method of multiplying and
91   taking the remainder.  The register is initialized to zero, and for each
92   incoming bit, x^32 is added mod p to the register if the bit is a one (where
93   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
94   x (which is shifting right by one and adding x^32 mod p if the bit shifted
95   out is a one).  We start with the highest power (least significant bit) of
96   q and repeat for all eight bits of q.
97 
98   The first table is simply the CRC of all possible eight bit values.  This is
99   all the information needed to generate CRCs on data a byte at a time for all
100   combinations of CRC register values and incoming bytes.  The remaining tables
101   allow for word-at-a-time CRC calculation for both big-endian and little-
102   endian machines, where a word is four bytes.
103 */
make_crc_table()104 local void make_crc_table()
105 {
106     unsigned long c;
107     int n, k;
108     unsigned long poly;            /* polynomial exclusive-or pattern */
109     /* terms of polynomial defining this crc (except x^32): */
110     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
111 
112     /* make exclusive-or pattern from polynomial (0xedb88320UL) */
113     poly = 0UL;
114     for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
115         poly |= 1UL << (31 - p[n]);
116 
117     /* generate a crc for every 8-bit value */
118     for (n = 0; n < 256; n++) {
119         c = (unsigned long)n;
120         for (k = 0; k < 8; k++)
121             c = c & 1 ? poly ^ (c >> 1) : c >> 1;
122         crc_table[0][n] = c;
123     }
124 
125 #ifdef BYFOUR
126     /* generate crc for each value followed by one, two, and three zeros, and
127        then the byte reversal of those as well as the first table */
128     for (n = 0; n < 256; n++) {
129         c = crc_table[0][n];
130         crc_table[4][n] = REV(c);
131         for (k = 1; k < 4; k++) {
132             c = crc_table[0][c & 0xff] ^ (c >> 8);
133             crc_table[k][n] = c;
134             crc_table[k + 4][n] = REV(c);
135         }
136     }
137 #endif /* BYFOUR */
138 
139   crc_table_empty = 0;
140 
141 #ifdef MAKECRCH
142     /* write out CRC tables to crc32.h */
143     {
144         FILE *out;
145 
146         out = fopen("crc32.h", "w");
147         if (out == NULL) return;
148         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
149         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
150         fprintf(out, "local const unsigned long FAR ");
151         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
152         write_table(out, crc_table[0]);
153 #  ifdef BYFOUR
154         fprintf(out, "#ifdef BYFOUR\n");
155         for (k = 1; k < 8; k++) {
156             fprintf(out, "  },\n  {\n");
157             write_table(out, crc_table[k]);
158         }
159         fprintf(out, "#endif\n");
160 #  endif /* BYFOUR */
161         fprintf(out, "  }\n};\n");
162         fclose(out);
163     }
164 #endif /* MAKECRCH */
165 }
166 
167 #ifdef MAKECRCH
write_table(out,table)168 local void write_table(out, table)
169     FILE *out;
170     const unsigned long FAR *table;
171 {
172     int n;
173 
174     for (n = 0; n < 256; n++)
175         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
176                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
177 }
178 #endif /* MAKECRCH */
179 
180 #else /* !DYNAMIC_CRC_TABLE */
181 /* ========================================================================
182  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
183  */
184 #include "crc32tbl.h"
185 #endif /* DYNAMIC_CRC_TABLE */
186 
187 /* ========================================================================= */
188 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
189 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
190 
191 
192 
193 /* ========================================================================= */
crc32(crc,buf,len)194 unsigned long ZEXPORT crc32(crc, buf, len)
195     unsigned long crc;
196     const unsigned char FAR *buf;
197     unsigned len;
198 {
199     if (buf == Z_NULL) return 0UL;
200 
201 #ifdef DYNAMIC_CRC_TABLE
202     if (crc_table_empty)
203         make_crc_table();
204 #endif /* DYNAMIC_CRC_TABLE */
205 
206 #ifdef BYFOUR
207     if (sizeof(void *) == sizeof(ptrdiff_t)) {
208         u4 endian;
209 
210         endian = 1;
211         if (*((unsigned char *)(&endian)))
212             return crc32_little(crc, buf, len);
213         else
214             return crc32_big(crc, buf, len);
215     }
216 #endif /* BYFOUR */
217     crc = crc ^ 0xffffffffUL;
218     while (len >= 8) {
219         DO8;
220         len -= 8;
221     }
222     if (len) do {
223         DO1;
224     } while (--len);
225     return crc ^ 0xffffffffUL;
226 }
227 
228 #ifdef BYFOUR
229 
230 /* ========================================================================= */
231 #define DOLIT4 c ^= *buf4++; \
232         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
233             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
234 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
235 
236 /* ========================================================================= */
crc32_little(crc,buf,len)237 local unsigned long crc32_little(crc, buf, len)
238     unsigned long crc;
239     const unsigned char FAR *buf;
240     unsigned len;
241 {
242     register u4 c;
243     register const u4 FAR *buf4;
244 
245     c = (u4)crc;
246     c = ~c;
247     while (len && ((ptrdiff_t)buf & 3)) {
248         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
249         len--;
250     }
251 
252     buf4 = (const u4 FAR *)(void *)buf;
253     while (len >= 32) {
254         DOLIT32;
255         len -= 32;
256     }
257     while (len >= 4) {
258         DOLIT4;
259         len -= 4;
260     }
261     buf = (const unsigned char FAR *)buf4;
262 
263     if (len) do {
264         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
265     } while (--len);
266     c = ~c;
267     return (unsigned long)c;
268 }
269 
270 /* ========================================================================= */
271 #define DOBIG4 c ^= *++buf4; \
272         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
273             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
274 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
275 
276 /* ========================================================================= */
crc32_big(crc,buf,len)277 local unsigned long crc32_big(crc, buf, len)
278     unsigned long crc;
279     const unsigned char FAR *buf;
280     unsigned len;
281 {
282     register u4 c;
283     register const u4 FAR *buf4;
284 
285     c = REV((u4)crc);
286     c = ~c;
287     while (len && ((ptrdiff_t)buf & 3)) {
288         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
289         len--;
290     }
291 
292     buf4 = (const u4 FAR *)(void *)buf;
293     buf4--;
294     while (len >= 32) {
295         DOBIG32;
296         len -= 32;
297     }
298     while (len >= 4) {
299         DOBIG4;
300         len -= 4;
301     }
302     buf4++;
303     buf = (const unsigned char FAR *)buf4;
304 
305     if (len) do {
306         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
307     } while (--len);
308     c = ~c;
309     return (unsigned long)(REV(c));
310 }
311 
312 #endif /* BYFOUR */
313