| OLD | NEW |
|---|
| (Empty) |
| 1 /* adler32.c -- compute the Adler-32 checksum of a data stream | |
| 2 * Copyright (C) 1995-2004 Mark Adler | |
| 3 * For conditions of distribution and use, see copyright notice in zlib.h | |
| 4 */ | |
| 5 | |
| 6 /* @(#) $Id$ */ | |
| 7 | |
| 8 #define ZLIB_INTERNAL | |
| 9 #include "zlib.h" | |
| 10 | |
| 11 #define BASE 65521UL /* largest prime smaller than 65536 */ | |
| 12 #define NMAX 5552 | |
| 13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ | |
| 14 | |
| 15 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} | |
| 16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); | |
| 17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); | |
| 18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); | |
| 19 #define DO16(buf) DO8(buf,0); DO8(buf,8); | |
| 20 | |
| 21 /* use NO_DIVIDE if your processor does not do division in hardware */ | |
| 22 #ifdef NO_DIVIDE | |
| 23 # define MOD(a) \ | |
| 24 do { \ | |
| 25 if (a >= (BASE << 16)) a -= (BASE << 16); \ | |
| 26 if (a >= (BASE << 15)) a -= (BASE << 15); \ | |
| 27 if (a >= (BASE << 14)) a -= (BASE << 14); \ | |
| 28 if (a >= (BASE << 13)) a -= (BASE << 13); \ | |
| 29 if (a >= (BASE << 12)) a -= (BASE << 12); \ | |
| 30 if (a >= (BASE << 11)) a -= (BASE << 11); \ | |
| 31 if (a >= (BASE << 10)) a -= (BASE << 10); \ | |
| 32 if (a >= (BASE << 9)) a -= (BASE << 9); \ | |
| 33 if (a >= (BASE << 8)) a -= (BASE << 8); \ | |
| 34 if (a >= (BASE << 7)) a -= (BASE << 7); \ | |
| 35 if (a >= (BASE << 6)) a -= (BASE << 6); \ | |
| 36 if (a >= (BASE << 5)) a -= (BASE << 5); \ | |
| 37 if (a >= (BASE << 4)) a -= (BASE << 4); \ | |
| 38 if (a >= (BASE << 3)) a -= (BASE << 3); \ | |
| 39 if (a >= (BASE << 2)) a -= (BASE << 2); \ | |
| 40 if (a >= (BASE << 1)) a -= (BASE << 1); \ | |
| 41 if (a >= BASE) a -= BASE; \ | |
| 42 } while (0) | |
| 43 # define MOD4(a) \ | |
| 44 do { \ | |
| 45 if (a >= (BASE << 4)) a -= (BASE << 4); \ | |
| 46 if (a >= (BASE << 3)) a -= (BASE << 3); \ | |
| 47 if (a >= (BASE << 2)) a -= (BASE << 2); \ | |
| 48 if (a >= (BASE << 1)) a -= (BASE << 1); \ | |
| 49 if (a >= BASE) a -= BASE; \ | |
| 50 } while (0) | |
| 51 #else | |
| 52 # define MOD(a) a %= BASE | |
| 53 # define MOD4(a) a %= BASE | |
| 54 #endif | |
| 55 | |
| 56 /* ========================================================================= */ | |
| 57 | |
| 58 /* | |
| 59 The adler32 code below computes, in effect, | |
| 60 | |
| 61 uLong high = 0; | |
| 62 uLong low = 1; | |
| 63 for (j = 0; j < len; j++) { | |
| 64 low = (low + buf[j]) % BASE; | |
| 65 high = (high + low) % BASE; | |
| 66 } | |
| 67 checksum = (high << 16) | low; | |
| 68 | |
| 69 Both 16-bit halves of the checksum are between 0 and BASE-1 (inclusive). | |
| 70 Hence, the minimum possible checksum value is 0, and the maximum is | |
| 71 ((BASE-1) << 16) | (BASE-1). Applications may have reserved values | |
| 72 outside this range to carry special meanings. | |
| 73 | |
| 74 NOTE: If adler32() is changed in ANY way, be absolutely sure that the | |
| 75 change will NOT cause checksums previously stored to not match the data | |
| 76 they were originally intended to match, or expand the range in such a | |
| 77 way that values reserved by applications to carry special meanings now | |
| 78 become checksums of valid data. Also, be sure to change adler32_range() | |
| 79 accordingly. | |
| 80 | |
| 81 This explanation and adler32_range() are not part of original software | |
| 82 distribution. They are added at Google (2006) in accordance with the | |
| 83 copyright notice in zlib.h, which permits alteration and redistribution | |
| 84 of the original software provided, among other things, that altered | |
| 85 source versions must be plainly marked as such and not misrepresented as | |
| 86 being the original software. | |
| 87 */ | |
| 88 | |
| 89 void ZEXPORT adler32_range(min, max) | |
| 90 uLong *min; | |
| 91 uLong *max; | |
| 92 { | |
| 93 *min = 0L; | |
| 94 *max = ((BASE-1) << 16) | (BASE-1); | |
| 95 } | |
| 96 | |
| 97 uLong ZEXPORT adler32(adler, buf, len) | |
| 98 uLong adler; | |
| 99 const Bytef *buf; | |
| 100 uInt len; | |
| 101 { | |
| 102 unsigned long sum2; | |
| 103 unsigned n; | |
| 104 | |
| 105 /* split Adler-32 into component sums */ | |
| 106 sum2 = (adler >> 16) & 0xffff; | |
| 107 adler &= 0xffff; | |
| 108 | |
| 109 /* in case user likes doing a byte at a time, keep it fast */ | |
| 110 if (len == 1) { | |
| 111 adler += buf[0]; | |
| 112 if (adler >= BASE) | |
| 113 adler -= BASE; | |
| 114 sum2 += adler; | |
| 115 if (sum2 >= BASE) | |
| 116 sum2 -= BASE; | |
| 117 return adler | (sum2 << 16); | |
| 118 } | |
| 119 | |
| 120 /* initial Adler-32 value (deferred check for len == 1 speed) */ | |
| 121 if (buf == Z_NULL) | |
| 122 return 1L; | |
| 123 | |
| 124 /* in case short lengths are provided, keep it somewhat fast */ | |
| 125 if (len < 16) { | |
| 126 while (len--) { | |
| 127 adler += *buf++; | |
| 128 sum2 += adler; | |
| 129 } | |
| 130 if (adler >= BASE) | |
| 131 adler -= BASE; | |
| 132 MOD4(sum2); /* only added so many BASE's */ | |
| 133 return adler | (sum2 << 16); | |
| 134 } | |
| 135 | |
| 136 /* do length NMAX blocks -- requires just one modulo operation */ | |
| 137 while (len >= NMAX) { | |
| 138 len -= NMAX; | |
| 139 n = NMAX / 16; /* NMAX is divisible by 16 */ | |
| 140 do { | |
| 141 DO16(buf); /* 16 sums unrolled */ | |
| 142 buf += 16; | |
| 143 } while (--n); | |
| 144 MOD(adler); | |
| 145 MOD(sum2); | |
| 146 } | |
| 147 | |
| 148 /* do remaining bytes (less than NMAX, still just one modulo) */ | |
| 149 if (len) { /* avoid modulos if none remaining */ | |
| 150 while (len >= 16) { | |
| 151 len -= 16; | |
| 152 DO16(buf); | |
| 153 buf += 16; | |
| 154 } | |
| 155 while (len--) { | |
| 156 adler += *buf++; | |
| 157 sum2 += adler; | |
| 158 } | |
| 159 MOD(adler); | |
| 160 MOD(sum2); | |
| 161 } | |
| 162 | |
| 163 /* return recombined sums */ | |
| 164 return adler | (sum2 << 16); | |
| 165 } | |
| 166 | |
| 167 /* ========================================================================= */ | |
| 168 uLong ZEXPORT adler32_combine(adler1, adler2, len2) | |
| 169 uLong adler1; | |
| 170 uLong adler2; | |
| 171 z_off_t len2; | |
| 172 { | |
| 173 unsigned long sum1; | |
| 174 unsigned long sum2; | |
| 175 unsigned rem; | |
| 176 | |
| 177 /* the derivation of this formula is left as an exercise for the reader */ | |
| 178 rem = (unsigned)(len2 % BASE); | |
| 179 sum1 = adler1 & 0xffff; | |
| 180 sum2 = rem * sum1; | |
| 181 MOD(sum2); | |
| 182 sum1 += (adler2 & 0xffff) + BASE - 1; | |
| 183 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; | |
| 184 if (sum1 >= BASE) sum1 -= BASE; | |
| 185 if (sum1 >= BASE) sum1 -= BASE; | |
| 186 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1); | |
| 187 if (sum2 >= BASE) sum2 -= BASE; | |
| 188 return sum1 | (sum2 << 16); | |
| 189 } | |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 5203:
Transition to pulling open-vcdiff from repository, instead of using snapshot... (Closed)
Base URL: svn://chrome-svn/chrome/trunk/src/