aboutsummaryrefslogtreecommitdiffstats log msg author committer range
 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 ``` ``````/* adler32.c -- compute the Adler-32 checksum of a data stream * Copyright (C) 1995-2004 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h */ #pragma ident "%Z%%M% %I% %E% SMI" #define ZLIB_INTERNAL #include "zlib.h" #define BASE 65521UL /* largest prime smaller than 65536 */ #define NMAX 5552 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); #define DO16(buf) DO8(buf,0); DO8(buf,8); /* use NO_DIVIDE if your processor does not do division in hardware */ #ifdef NO_DIVIDE # define MOD(a) \ do { \ if (a >= (BASE << 16)) a -= (BASE << 16); \ if (a >= (BASE << 15)) a -= (BASE << 15); \ if (a >= (BASE << 14)) a -= (BASE << 14); \ if (a >= (BASE << 13)) a -= (BASE << 13); \ if (a >= (BASE << 12)) a -= (BASE << 12); \ if (a >= (BASE << 11)) a -= (BASE << 11); \ if (a >= (BASE << 10)) a -= (BASE << 10); \ if (a >= (BASE << 9)) a -= (BASE << 9); \ if (a >= (BASE << 8)) a -= (BASE << 8); \ if (a >= (BASE << 7)) a -= (BASE << 7); \ if (a >= (BASE << 6)) a -= (BASE << 6); \ if (a >= (BASE << 5)) a -= (BASE << 5); \ if (a >= (BASE << 4)) a -= (BASE << 4); \ if (a >= (BASE << 3)) a -= (BASE << 3); \ if (a >= (BASE << 2)) a -= (BASE << 2); \ if (a >= (BASE << 1)) a -= (BASE << 1); \ if (a >= BASE) a -= BASE; \ } while (0) # define MOD4(a) \ do { \ if (a >= (BASE << 4)) a -= (BASE << 4); \ if (a >= (BASE << 3)) a -= (BASE << 3); \ if (a >= (BASE << 2)) a -= (BASE << 2); \ if (a >= (BASE << 1)) a -= (BASE << 1); \ if (a >= BASE) a -= BASE; \ } while (0) #else # define MOD(a) a %= BASE # define MOD4(a) a %= BASE #endif /* ========================================================================= */ uLong ZEXPORT adler32(adler, buf, len) uLong adler; const Bytef *buf; uInt len; { unsigned long sum2; unsigned n; /* split Adler-32 into component sums */ sum2 = (adler >> 16) & 0xffff; adler &= 0xffff; /* in case user likes doing a byte at a time, keep it fast */ if (len == 1) { adler += buf[0]; if (adler >= BASE) adler -= BASE; sum2 += adler; if (sum2 >= BASE) sum2 -= BASE; return adler | (sum2 << 16); } /* initial Adler-32 value (deferred check for len == 1 speed) */ if (buf == Z_NULL) return 1L; /* in case short lengths are provided, keep it somewhat fast */ if (len < 16) { while (len--) { adler += *buf++; sum2 += adler; } if (adler >= BASE) adler -= BASE; MOD4(sum2); /* only added so many BASE's */ return adler | (sum2 << 16); } /* do length NMAX blocks -- requires just one modulo operation */ while (len >= NMAX) { len -= NMAX; n = NMAX / 16; /* NMAX is divisible by 16 */ do { DO16(buf); /* 16 sums unrolled */ buf += 16; } while (--n); MOD(adler); MOD(sum2); } /* do remaining bytes (less than NMAX, still just one modulo) */ if (len) { /* avoid modulos if none remaining */ while (len >= 16) { len -= 16; DO16(buf); buf += 16; } while (len--) { adler += *buf++; sum2 += adler; } MOD(adler); MOD(sum2); } /* return recombined sums */ return adler | (sum2 << 16); } /* ========================================================================= */ uLong ZEXPORT adler32_combine(adler1, adler2, len2) uLong adler1; uLong adler2; z_off_t len2; { unsigned long sum1; unsigned long sum2; unsigned rem; /* the derivation of this formula is left as an exercise for the reader */ rem = (unsigned)(len2 % BASE); sum1 = adler1 & 0xffff; sum2 = rem * sum1; MOD(sum2); sum1 += (adler2 & 0xffff) + BASE - 1; sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; if (sum1 > BASE) sum1 -= BASE; if (sum1 > BASE) sum1 -= BASE; if (sum2 > (BASE << 1)) sum2 -= (BASE << 1); if (sum2 > BASE) sum2 -= BASE; return sum1 | (sum2 << 16); } ``````