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| 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: adler32.c,v 3.6 2005/08/04 19:14:14 tor%cs.brown.edu Exp $ */ |
| 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 | +uLong ZEXPORT adler32(adler, buf, len) |
| 58 | + uLong adler; |
| 59 | + const Bytef *buf; |
| 60 | + uInt len; |
| 61 | +{ |
| 62 | + unsigned long sum2; |
| 63 | + unsigned n; |
| 64 | + |
| 65 | + /* split Adler-32 into component sums */ |
| 66 | + sum2 = (adler >> 16) & 0xffff; |
| 67 | + adler &= 0xffff; |
| 68 | + |
| 69 | + /* in case user likes doing a byte at a time, keep it fast */ |
| 70 | + if (len == 1) { |
| 71 | + adler += buf[0]; |
| 72 | + if (adler >= BASE) |
| 73 | + adler -= BASE; |
| 74 | + sum2 += adler; |
| 75 | + if (sum2 >= BASE) |
| 76 | + sum2 -= BASE; |
| 77 | + return adler | (sum2 << 16); |
| 78 | + } |
| 79 | + |
| 80 | + /* initial Adler-32 value (deferred check for len == 1 speed) */ |
| 81 | + if (buf == Z_NULL) |
| 82 | + return 1L; |
| 83 | + |
| 84 | + /* in case short lengths are provided, keep it somewhat fast */ |
| 85 | + if (len < 16) { |
| 86 | + while (len--) { |
| 87 | + adler += *buf++; |
| 88 | + sum2 += adler; |
| 89 | + } |
| 90 | + if (adler >= BASE) |
| 91 | + adler -= BASE; |
| 92 | + MOD4(sum2); /* only added so many BASE's */ |
| 93 | + return adler | (sum2 << 16); |
| 94 | + } |
| 95 | + |
| 96 | + /* do length NMAX blocks -- requires just one modulo operation */ |
| 97 | + while (len >= NMAX) { |
| 98 | + len -= NMAX; |
| 99 | + n = NMAX / 16; /* NMAX is divisible by 16 */ |
| 100 | + do { |
| 101 | + DO16(buf); /* 16 sums unrolled */ |
| 102 | + buf += 16; |
| 103 | + } while (--n); |
| 104 | + MOD(adler); |
| 105 | + MOD(sum2); |
| 106 | + } |
| 107 | + |
| 108 | + /* do remaining bytes (less than NMAX, still just one modulo) */ |
| 109 | + if (len) { /* avoid modulos if none remaining */ |
| 110 | + while (len >= 16) { |
| 111 | + len -= 16; |
| 112 | + DO16(buf); |
| 113 | + buf += 16; |
| 114 | + } |
| 115 | + while (len--) { |
| 116 | + adler += *buf++; |
| 117 | + sum2 += adler; |
| 118 | + } |
| 119 | + MOD(adler); |
| 120 | + MOD(sum2); |
| 121 | + } |
| 122 | + |
| 123 | + /* return recombined sums */ |
| 124 | + return adler | (sum2 << 16); |
| 125 | +} |
| 126 | + |
| 127 | +/* ========================================================================= */ |
| 128 | +uLong ZEXPORT adler32_combine(adler1, adler2, len2) |
| 129 | + uLong adler1; |
| 130 | + uLong adler2; |
| 131 | + z_off_t len2; |
| 132 | +{ |
| 133 | + unsigned long sum1; |
| 134 | + unsigned long sum2; |
| 135 | + unsigned rem; |
| 136 | + |
| 137 | + /* the derivation of this formula is left as an exercise for the reader */ |
| 138 | + rem = (unsigned)(len2 % BASE); |
| 139 | + sum1 = adler1 & 0xffff; |
| 140 | + sum2 = rem * sum1; |
| 141 | + MOD(sum2); |
| 142 | + sum1 += (adler2 & 0xffff) + BASE - 1; |
| 143 | + sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; |
| 144 | + if (sum1 > BASE) sum1 -= BASE; |
| 145 | + if (sum1 > BASE) sum1 -= BASE; |
| 146 | + if (sum2 > (BASE << 1)) sum2 -= (BASE << 1); |
| 147 | + if (sum2 > BASE) sum2 -= BASE; |
| 148 | + return sum1 | (sum2 << 16); |
| 149 | +} |
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