1/*
2 * Copyright (c) 2008 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28/* crc32.c -- compute the CRC-32 of a data stream
29 * Copyright (C) 1995-2005 Mark Adler
30 * For conditions of distribution and use, see copyright notice in zlib.h
31 *
32 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
33 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
34 * tables for updating the shift register in one step with three exclusive-ors
35 * instead of four steps with four exclusive-ors.  This results in about a
36 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
37 */
38
39/* @(#) $Id$ */
40
41/*
42  Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
43  protection on the static variables used to control the first-use generation
44  of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
45  first call get_crc_table() to initialize the tables before allowing more than
46  one thread to use crc32().
47 */
48
49#ifdef MAKECRCH
50#  include <stdio.h>
51#  ifndef DYNAMIC_CRC_TABLE
52#    define DYNAMIC_CRC_TABLE
53#  endif /* !DYNAMIC_CRC_TABLE */
54#endif /* MAKECRCH */
55
56#include "zutil.h"      /* for STDC and FAR definitions */
57
58#define local static
59
60/* Find a four-byte integer type for crc32_little() and crc32_big(). */
61#ifndef NOBYFOUR
62#  ifdef STDC           /* need ANSI C limits.h to determine sizes */
63#    include <machine/limits.h>
64#    define BYFOUR
65#    if (UINT_MAX == 0xffffffffUL)
66       typedef unsigned int u4;
67#    else
68#      if (ULONG_MAX == 0xffffffffUL)
69         typedef unsigned long u4;
70#      else
71#        if (USHRT_MAX == 0xffffffffUL)
72           typedef unsigned short u4;
73#        else
74#          undef BYFOUR     /* can't find a four-byte integer type! */
75#        endif
76#      endif
77#    endif
78#  endif /* STDC */
79#endif /* !NOBYFOUR */
80
81/* Definitions for doing the crc four data bytes at a time. */
82#ifdef BYFOUR
83#  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
84                (((w)&0xff00)<<8)+(((w)&0xff)<<24))
85   local unsigned long crc32_little OF((unsigned long,
86                        const unsigned char FAR *, unsigned));
87   local unsigned long crc32_big OF((unsigned long,
88                        const unsigned char FAR *, unsigned));
89#  define TBLS 8
90#else
91#  define TBLS 1
92#endif /* BYFOUR */
93
94/* Local functions for crc concatenation */
95local unsigned long gf2_matrix_times OF((unsigned long *mat,
96                                         unsigned long vec));
97local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
98
99#ifdef DYNAMIC_CRC_TABLE
100
101local volatile int crc_table_empty = 1;
102local unsigned long FAR crc_table[TBLS][256];
103local void make_crc_table OF((void));
104#ifdef MAKECRCH
105   local void write_table OF((FILE *, const unsigned long FAR *));
106#endif /* MAKECRCH */
107/*
108  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
109  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.
110
111  Polynomials over GF(2) are represented in binary, one bit per coefficient,
112  with the lowest powers in the most significant bit.  Then adding polynomials
113  is just exclusive-or, and multiplying a polynomial by x is a right shift by
114  one.  If we call the above polynomial p, and represent a byte as the
115  polynomial q, also with the lowest power in the most significant bit (so the
116  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
117  where a mod b means the remainder after dividing a by b.
118
119  This calculation is done using the shift-register method of multiplying and
120  taking the remainder.  The register is initialized to zero, and for each
121  incoming bit, x^32 is added mod p to the register if the bit is a one (where
122  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
123  x (which is shifting right by one and adding x^32 mod p if the bit shifted
124  out is a one).  We start with the highest power (least significant bit) of
125  q and repeat for all eight bits of q.
126
127  The first table is simply the CRC of all possible eight bit values.  This is
128  all the information needed to generate CRCs on data a byte at a time for all
129  combinations of CRC register values and incoming bytes.  The remaining tables
130  allow for word-at-a-time CRC calculation for both big-endian and little-
131  endian machines, where a word is four bytes.
132*/
133local void make_crc_table()
134{
135    unsigned long c;
136    int n, k;
137    unsigned long poly;                 /* polynomial exclusive-or pattern */
138    /* terms of polynomial defining this crc (except x^32): */
139    static volatile int first = 1;      /* flag to limit concurrent making */
140    static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
141
142    /* See if another task is already doing this (not thread-safe, but better
143       than nothing -- significantly reduces duration of vulnerability in
144       case the advice about DYNAMIC_CRC_TABLE is ignored) */
145    if (first) {
146        first = 0;
147
148        /* make exclusive-or pattern from polynomial (0xedb88320UL) */
149        poly = 0UL;
150        for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
151            poly |= 1UL << (31 - p[n]);
152
153        /* generate a crc for every 8-bit value */
154        for (n = 0; n < 256; n++) {
155            c = (unsigned long)n;
156            for (k = 0; k < 8; k++)
157                c = c & 1 ? poly ^ (c >> 1) : c >> 1;
158            crc_table[0][n] = c;
159        }
160
161#ifdef BYFOUR
162        /* generate crc for each value followed by one, two, and three zeros,
163           and then the byte reversal of those as well as the first table */
164        for (n = 0; n < 256; n++) {
165            c = crc_table[0][n];
166            crc_table[4][n] = REV(c);
167            for (k = 1; k < 4; k++) {
168                c = crc_table[0][c & 0xff] ^ (c >> 8);
169                crc_table[k][n] = c;
170                crc_table[k + 4][n] = REV(c);
171            }
172        }
173#endif /* BYFOUR */
174
175        crc_table_empty = 0;
176    }
177    else {      /* not first */
178        /* wait for the other guy to finish (not efficient, but rare) */
179        while (crc_table_empty)
180            ;
181    }
182
183#ifdef MAKECRCH
184    /* write out CRC tables to crc32.h */
185    {
186        FILE *out;
187
188        out = fopen("crc32.h", "w");
189        if (out == NULL) return;
190        fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
191        fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
192        fprintf(out, "local const unsigned long FAR ");
193        fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
194        write_table(out, crc_table[0]);
195#  ifdef BYFOUR
196        fprintf(out, "#ifdef BYFOUR\n");
197        for (k = 1; k < 8; k++) {
198            fprintf(out, "  },\n  {\n");
199            write_table(out, crc_table[k]);
200        }
201        fprintf(out, "#endif\n");
202#  endif /* BYFOUR */
203        fprintf(out, "  }\n};\n");
204        fclose(out);
205    }
206#endif /* MAKECRCH */
207}
208
209#ifdef MAKECRCH
210local void write_table(out, table)
211    FILE *out;
212    const unsigned long FAR *table;
213{
214    int n;
215
216    for (n = 0; n < 256; n++)
217        fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
218                n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
219}
220#endif /* MAKECRCH */
221
222#else /* !DYNAMIC_CRC_TABLE */
223/* ========================================================================
224 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
225 */
226#include "crc32.h"
227#endif /* DYNAMIC_CRC_TABLE */
228
229/* =========================================================================
230 * This function can be used by asm versions of crc32()
231 */
232const unsigned long FAR * ZEXPORT get_crc_table()
233{
234#ifdef DYNAMIC_CRC_TABLE
235    if (crc_table_empty)
236        make_crc_table();
237#endif /* DYNAMIC_CRC_TABLE */
238    return (const unsigned long FAR *)crc_table;
239}
240
241/* ========================================================================= */
242#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
243#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
244
245/* ========================================================================= */
246unsigned long ZEXPORT z_crc32(crc, buf, len)
247    unsigned long crc;
248    const unsigned char FAR *buf;
249    unsigned len;
250{
251    if (buf == Z_NULL) return 0UL;
252
253#ifdef DYNAMIC_CRC_TABLE
254    if (crc_table_empty)
255        make_crc_table();
256#endif /* DYNAMIC_CRC_TABLE */
257
258#ifdef BYFOUR
259    if (sizeof(void *) == sizeof(ptrdiff_t)) {
260        u4 endian;
261
262        endian = 1;
263        if (*((unsigned char *)(&endian)))
264            return crc32_little(crc, buf, len);
265        else
266            return crc32_big(crc, buf, len);
267    }
268#endif /* BYFOUR */
269    crc = crc ^ 0xffffffffUL;
270    while (len >= 8) {
271        DO8;
272        len -= 8;
273    }
274    if (len) do {
275        DO1;
276    } while (--len);
277    return crc ^ 0xffffffffUL;
278}
279
280#ifdef BYFOUR
281
282/* ========================================================================= */
283#define DOLIT4 c ^= *buf4++; \
284        c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
285            crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
286#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
287
288/* ========================================================================= */
289local unsigned long crc32_little(crc, buf, len)
290    unsigned long crc;
291    const unsigned char FAR *buf;
292    unsigned len;
293{
294    register u4 c;
295    register const u4 FAR *buf4;
296
297    c = (u4)crc;
298    c = ~c;
299    while (len && ((ptrdiff_t)buf & 3)) {
300        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
301        len--;
302    }
303
304    buf4 = (const u4 FAR *)(const void FAR *)buf;
305    while (len >= 32) {
306        DOLIT32;
307        len -= 32;
308    }
309    while (len >= 4) {
310        DOLIT4;
311        len -= 4;
312    }
313    buf = (const unsigned char FAR *)buf4;
314
315    if (len) do {
316        c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
317    } while (--len);
318    c = ~c;
319    return (unsigned long)c;
320}
321
322/* ========================================================================= */
323#define DOBIG4 c ^= *++buf4; \
324        c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
325            crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
326#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
327
328/* ========================================================================= */
329local unsigned long crc32_big(crc, buf, len)
330    unsigned long crc;
331    const unsigned char FAR *buf;
332    unsigned len;
333{
334    register u4 c;
335    register const u4 FAR *buf4;
336
337    c = REV((u4)crc);
338    c = ~c;
339    while (len && ((ptrdiff_t)buf & 3)) {
340        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
341        len--;
342    }
343
344    buf4 = (const u4 FAR *)(const void FAR *)buf;
345    buf4--;
346    while (len >= 32) {
347        DOBIG32;
348        len -= 32;
349    }
350    while (len >= 4) {
351        DOBIG4;
352        len -= 4;
353    }
354    buf4++;
355    buf = (const unsigned char FAR *)buf4;
356
357    if (len) do {
358        c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
359    } while (--len);
360    c = ~c;
361    return (unsigned long)(REV(c));
362}
363
364#endif /* BYFOUR */
365
366#define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
367
368/* ========================================================================= */
369local unsigned long gf2_matrix_times(mat, vec)
370    unsigned long *mat;
371    unsigned long vec;
372{
373    unsigned long sum;
374
375    sum = 0;
376    while (vec) {
377        if (vec & 1)
378            sum ^= *mat;
379        vec >>= 1;
380        mat++;
381    }
382    return sum;
383}
384
385/* ========================================================================= */
386local void gf2_matrix_square(square, mat)
387    unsigned long *square;
388    unsigned long *mat;
389{
390    int n;
391
392    for (n = 0; n < GF2_DIM; n++)
393        square[n] = gf2_matrix_times(mat, mat[n]);
394}
395
396/* ========================================================================= */
397uLong ZEXPORT z_crc32_combine(crc1, crc2, len2)
398    uLong crc1;
399    uLong crc2;
400    z_off_t len2;
401{
402    int n;
403    unsigned long row;
404    unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
405    unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
406
407    /* degenerate case */
408    if (len2 == 0)
409        return crc1;
410
411    /* put operator for one zero bit in odd */
412    odd[0] = 0xedb88320L;           /* CRC-32 polynomial */
413    row = 1;
414    for (n = 1; n < GF2_DIM; n++) {
415        odd[n] = row;
416        row <<= 1;
417    }
418
419    /* put operator for two zero bits in even */
420    gf2_matrix_square(even, odd);
421
422    /* put operator for four zero bits in odd */
423    gf2_matrix_square(odd, even);
424
425    /* apply len2 zeros to crc1 (first square will put the operator for one
426       zero byte, eight zero bits, in even) */
427    do {
428        /* apply zeros operator for this bit of len2 */
429        gf2_matrix_square(even, odd);
430        if (len2 & 1)
431            crc1 = gf2_matrix_times(even, crc1);
432        len2 >>= 1;
433
434        /* if no more bits set, then done */
435        if (len2 == 0)
436            break;
437
438        /* another iteration of the loop with odd and even swapped */
439        gf2_matrix_square(odd, even);
440        if (len2 & 1)
441            crc1 = gf2_matrix_times(odd, crc1);
442        len2 >>= 1;
443
444        /* if no more bits set, then done */
445    } while (len2 != 0);
446
447    /* return combined crc */
448    crc1 ^= crc2;
449    return crc1;
450}
451