Annotation of embedaddon/sudo/zlib/adler32.c, revision 1.1
1.1 ! misho 1: /* adler32.c -- compute the Adler-32 checksum of a data stream
! 2: * Copyright (C) 1995-2007 Mark Adler
! 3: * For conditions of distribution and use, see copyright notice in zlib.h
! 4: */
! 5:
! 6: /* @(#) $Id$ */
! 7:
! 8: #include "zutil.h"
! 9:
! 10: #define local static
! 11:
! 12: local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
! 13:
! 14: #define BASE 65521UL /* largest prime smaller than 65536 */
! 15: #define NMAX 5552
! 16: /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
! 17:
! 18: #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
! 19: #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
! 20: #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
! 21: #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
! 22: #define DO16(buf) DO8(buf,0); DO8(buf,8);
! 23:
! 24: /* use NO_DIVIDE if your processor does not do division in hardware */
! 25: #ifdef NO_DIVIDE
! 26: # define MOD(a) \
! 27: do { \
! 28: if (a >= (BASE << 16)) a -= (BASE << 16); \
! 29: if (a >= (BASE << 15)) a -= (BASE << 15); \
! 30: if (a >= (BASE << 14)) a -= (BASE << 14); \
! 31: if (a >= (BASE << 13)) a -= (BASE << 13); \
! 32: if (a >= (BASE << 12)) a -= (BASE << 12); \
! 33: if (a >= (BASE << 11)) a -= (BASE << 11); \
! 34: if (a >= (BASE << 10)) a -= (BASE << 10); \
! 35: if (a >= (BASE << 9)) a -= (BASE << 9); \
! 36: if (a >= (BASE << 8)) a -= (BASE << 8); \
! 37: if (a >= (BASE << 7)) a -= (BASE << 7); \
! 38: if (a >= (BASE << 6)) a -= (BASE << 6); \
! 39: if (a >= (BASE << 5)) a -= (BASE << 5); \
! 40: if (a >= (BASE << 4)) a -= (BASE << 4); \
! 41: if (a >= (BASE << 3)) a -= (BASE << 3); \
! 42: if (a >= (BASE << 2)) a -= (BASE << 2); \
! 43: if (a >= (BASE << 1)) a -= (BASE << 1); \
! 44: if (a >= BASE) a -= BASE; \
! 45: } while (0)
! 46: # define MOD4(a) \
! 47: do { \
! 48: if (a >= (BASE << 4)) a -= (BASE << 4); \
! 49: if (a >= (BASE << 3)) a -= (BASE << 3); \
! 50: if (a >= (BASE << 2)) a -= (BASE << 2); \
! 51: if (a >= (BASE << 1)) a -= (BASE << 1); \
! 52: if (a >= BASE) a -= BASE; \
! 53: } while (0)
! 54: #else
! 55: # define MOD(a) a %= BASE
! 56: # define MOD4(a) a %= BASE
! 57: #endif
! 58:
! 59: /* ========================================================================= */
! 60: uLong ZEXPORT adler32(adler, buf, len)
! 61: uLong adler;
! 62: const Bytef *buf;
! 63: uInt len;
! 64: {
! 65: unsigned long sum2;
! 66: unsigned n;
! 67:
! 68: /* split Adler-32 into component sums */
! 69: sum2 = (adler >> 16) & 0xffff;
! 70: adler &= 0xffff;
! 71:
! 72: /* in case user likes doing a byte at a time, keep it fast */
! 73: if (len == 1) {
! 74: adler += buf[0];
! 75: if (adler >= BASE)
! 76: adler -= BASE;
! 77: sum2 += adler;
! 78: if (sum2 >= BASE)
! 79: sum2 -= BASE;
! 80: return adler | (sum2 << 16);
! 81: }
! 82:
! 83: /* initial Adler-32 value (deferred check for len == 1 speed) */
! 84: if (buf == Z_NULL)
! 85: return 1L;
! 86:
! 87: /* in case short lengths are provided, keep it somewhat fast */
! 88: if (len < 16) {
! 89: while (len--) {
! 90: adler += *buf++;
! 91: sum2 += adler;
! 92: }
! 93: if (adler >= BASE)
! 94: adler -= BASE;
! 95: MOD4(sum2); /* only added so many BASE's */
! 96: return adler | (sum2 << 16);
! 97: }
! 98:
! 99: /* do length NMAX blocks -- requires just one modulo operation */
! 100: while (len >= NMAX) {
! 101: len -= NMAX;
! 102: n = NMAX / 16; /* NMAX is divisible by 16 */
! 103: do {
! 104: DO16(buf); /* 16 sums unrolled */
! 105: buf += 16;
! 106: } while (--n);
! 107: MOD(adler);
! 108: MOD(sum2);
! 109: }
! 110:
! 111: /* do remaining bytes (less than NMAX, still just one modulo) */
! 112: if (len) { /* avoid modulos if none remaining */
! 113: while (len >= 16) {
! 114: len -= 16;
! 115: DO16(buf);
! 116: buf += 16;
! 117: }
! 118: while (len--) {
! 119: adler += *buf++;
! 120: sum2 += adler;
! 121: }
! 122: MOD(adler);
! 123: MOD(sum2);
! 124: }
! 125:
! 126: /* return recombined sums */
! 127: return adler | (sum2 << 16);
! 128: }
! 129:
! 130: /* ========================================================================= */
! 131: local uLong adler32_combine_(adler1, adler2, len2)
! 132: uLong adler1;
! 133: uLong adler2;
! 134: z_off64_t len2;
! 135: {
! 136: unsigned long sum1;
! 137: unsigned long sum2;
! 138: unsigned rem;
! 139:
! 140: /* the derivation of this formula is left as an exercise for the reader */
! 141: rem = (unsigned)(len2 % BASE);
! 142: sum1 = adler1 & 0xffff;
! 143: sum2 = rem * sum1;
! 144: MOD(sum2);
! 145: sum1 += (adler2 & 0xffff) + BASE - 1;
! 146: sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
! 147: if (sum1 >= BASE) sum1 -= BASE;
! 148: if (sum1 >= BASE) sum1 -= BASE;
! 149: if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
! 150: if (sum2 >= BASE) sum2 -= BASE;
! 151: return sum1 | (sum2 << 16);
! 152: }
! 153:
! 154: /* ========================================================================= */
! 155: uLong ZEXPORT adler32_combine(adler1, adler2, len2)
! 156: uLong adler1;
! 157: uLong adler2;
! 158: z_off_t len2;
! 159: {
! 160: return adler32_combine_(adler1, adler2, len2);
! 161: }
! 162:
! 163: uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
! 164: uLong adler1;
! 165: uLong adler2;
! 166: z_off64_t len2;
! 167: {
! 168: return adler32_combine_(adler1, adler2, len2);
! 169: }
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