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modules/zlib/src/adler32.c@b8a032363ba2 (annotated)

modules/zlib/src/adler32.c

Thu, 22 Jan 2015 13:21:57 +0100

author
Michael Schloh von Bennewitz <michael@schloh.com>
date
Thu, 22 Jan 2015 13:21:57 +0100
branch
TOR_BUG_9701
changeset 15
b8a032363ba2
permissions
-rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

michael@0 1 /* adler32.c -- compute the Adler-32 checksum of a data stream
michael@0 2 * Copyright (C) 1995-2011 Mark Adler
michael@0 3 * For conditions of distribution and use, see copyright notice in zlib.h
michael@0 4 */
michael@0 5
michael@0 6 /* @(#) $Id$ */
michael@0 7
michael@0 8 #include "zutil.h"
michael@0 9
michael@0 10 #define local static
michael@0 11
michael@0 12 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
michael@0 13
michael@0 14 #define BASE 65521 /* largest prime smaller than 65536 */
michael@0 15 #define NMAX 5552
michael@0 16 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
michael@0 17
michael@0 18 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
michael@0 19 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
michael@0 20 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
michael@0 21 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
michael@0 22 #define DO16(buf) DO8(buf,0); DO8(buf,8);
michael@0 23
michael@0 24 /* use NO_DIVIDE if your processor does not do division in hardware --
michael@0 25 try it both ways to see which is faster */
michael@0 26 #ifdef NO_DIVIDE
michael@0 27 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
michael@0 28 (thank you to John Reiser for pointing this out) */
michael@0 29 # define CHOP(a) \
michael@0 30 do { \
michael@0 31 unsigned long tmp = a >> 16; \
michael@0 32 a &= 0xffffUL; \
michael@0 33 a += (tmp << 4) - tmp; \
michael@0 34 } while (0)
michael@0 35 # define MOD28(a) \
michael@0 36 do { \
michael@0 37 CHOP(a); \
michael@0 38 if (a >= BASE) a -= BASE; \
michael@0 39 } while (0)
michael@0 40 # define MOD(a) \
michael@0 41 do { \
michael@0 42 CHOP(a); \
michael@0 43 MOD28(a); \
michael@0 44 } while (0)
michael@0 45 # define MOD63(a) \
michael@0 46 do { /* this assumes a is not negative */ \
michael@0 47 z_off64_t tmp = a >> 32; \
michael@0 48 a &= 0xffffffffL; \
michael@0 49 a += (tmp << 8) - (tmp << 5) + tmp; \
michael@0 50 tmp = a >> 16; \
michael@0 51 a &= 0xffffL; \
michael@0 52 a += (tmp << 4) - tmp; \
michael@0 53 tmp = a >> 16; \
michael@0 54 a &= 0xffffL; \
michael@0 55 a += (tmp << 4) - tmp; \
michael@0 56 if (a >= BASE) a -= BASE; \
michael@0 57 } while (0)
michael@0 58 #else
michael@0 59 # define MOD(a) a %= BASE
michael@0 60 # define MOD28(a) a %= BASE
michael@0 61 # define MOD63(a) a %= BASE
michael@0 62 #endif
michael@0 63
michael@0 64 /* ========================================================================= */
michael@0 65 uLong ZEXPORT adler32(adler, buf, len)
michael@0 66 uLong adler;
michael@0 67 const Bytef *buf;
michael@0 68 uInt len;
michael@0 69 {
michael@0 70 unsigned long sum2;
michael@0 71 unsigned n;
michael@0 72
michael@0 73 /* split Adler-32 into component sums */
michael@0 74 sum2 = (adler >> 16) & 0xffff;
michael@0 75 adler &= 0xffff;
michael@0 76
michael@0 77 /* in case user likes doing a byte at a time, keep it fast */
michael@0 78 if (len == 1) {
michael@0 79 adler += buf[0];
michael@0 80 if (adler >= BASE)
michael@0 81 adler -= BASE;
michael@0 82 sum2 += adler;
michael@0 83 if (sum2 >= BASE)
michael@0 84 sum2 -= BASE;
michael@0 85 return adler | (sum2 << 16);
michael@0 86 }
michael@0 87
michael@0 88 /* initial Adler-32 value (deferred check for len == 1 speed) */
michael@0 89 if (buf == Z_NULL)
michael@0 90 return 1L;
michael@0 91
michael@0 92 /* in case short lengths are provided, keep it somewhat fast */
michael@0 93 if (len < 16) {
michael@0 94 while (len--) {
michael@0 95 adler += *buf++;
michael@0 96 sum2 += adler;
michael@0 97 }
michael@0 98 if (adler >= BASE)
michael@0 99 adler -= BASE;
michael@0 100 MOD28(sum2); /* only added so many BASE's */
michael@0 101 return adler | (sum2 << 16);
michael@0 102 }
michael@0 103
michael@0 104 /* do length NMAX blocks -- requires just one modulo operation */
michael@0 105 while (len >= NMAX) {
michael@0 106 len -= NMAX;
michael@0 107 n = NMAX / 16; /* NMAX is divisible by 16 */
michael@0 108 do {
michael@0 109 DO16(buf); /* 16 sums unrolled */
michael@0 110 buf += 16;
michael@0 111 } while (--n);
michael@0 112 MOD(adler);
michael@0 113 MOD(sum2);
michael@0 114 }
michael@0 115
michael@0 116 /* do remaining bytes (less than NMAX, still just one modulo) */
michael@0 117 if (len) { /* avoid modulos if none remaining */
michael@0 118 while (len >= 16) {
michael@0 119 len -= 16;
michael@0 120 DO16(buf);
michael@0 121 buf += 16;
michael@0 122 }
michael@0 123 while (len--) {
michael@0 124 adler += *buf++;
michael@0 125 sum2 += adler;
michael@0 126 }
michael@0 127 MOD(adler);
michael@0 128 MOD(sum2);
michael@0 129 }
michael@0 130
michael@0 131 /* return recombined sums */
michael@0 132 return adler | (sum2 << 16);
michael@0 133 }
michael@0 134
michael@0 135 /* ========================================================================= */
michael@0 136 local uLong adler32_combine_(adler1, adler2, len2)
michael@0 137 uLong adler1;
michael@0 138 uLong adler2;
michael@0 139 z_off64_t len2;
michael@0 140 {
michael@0 141 unsigned long sum1;
michael@0 142 unsigned long sum2;
michael@0 143 unsigned rem;
michael@0 144
michael@0 145 /* for negative len, return invalid adler32 as a clue for debugging */
michael@0 146 if (len2 < 0)
michael@0 147 return 0xffffffffUL;
michael@0 148
michael@0 149 /* the derivation of this formula is left as an exercise for the reader */
michael@0 150 MOD63(len2); /* assumes len2 >= 0 */
michael@0 151 rem = (unsigned)len2;
michael@0 152 sum1 = adler1 & 0xffff;
michael@0 153 sum2 = rem * sum1;
michael@0 154 MOD(sum2);
michael@0 155 sum1 += (adler2 & 0xffff) + BASE - 1;
michael@0 156 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
michael@0 157 if (sum1 >= BASE) sum1 -= BASE;
michael@0 158 if (sum1 >= BASE) sum1 -= BASE;
michael@0 159 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
michael@0 160 if (sum2 >= BASE) sum2 -= BASE;
michael@0 161 return sum1 | (sum2 << 16);
michael@0 162 }
michael@0 163
michael@0 164 /* ========================================================================= */
michael@0 165 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
michael@0 166 uLong adler1;
michael@0 167 uLong adler2;
michael@0 168 z_off_t len2;
michael@0 169 {
michael@0 170 return adler32_combine_(adler1, adler2, len2);
michael@0 171 }
michael@0 172
michael@0 173 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
michael@0 174 uLong adler1;
michael@0 175 uLong adler2;
michael@0 176 z_off64_t len2;
michael@0 177 {
michael@0 178 return adler32_combine_(adler1, adler2, len2);
michael@0 179 }

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