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