1 /* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2011 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 zRCSID("$MirOS: src/kern/z/adler32.c,v 1.8 2013/08/05 21:27:30 tg Exp $") 11 12 #define BASE 65521 /* largest prime smaller than 65536 */ 13 #define NMAX 5552 14 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 15 16 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 17 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 18 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 19 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 20 #define DO16(buf) DO8(buf,0); DO8(buf,8); 21 22 /* use NO_DIVIDE if your processor does not do division in hardware -- 23 try it both ways to see which is faster */ 24 #ifdef NO_DIVIDE 25 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 26 (thank you to John Reiser for pointing this out) */ 27 # define CHOP(a) \ 28 do { \ 29 unsigned long tmp = a >> 16; \ 30 a &= 0xffffUL; \ 31 a += (tmp << 4) - tmp; \ 32 } while (0) 33 # define MOD28(a) \ 34 do { \ 35 CHOP(a); \ 36 if (a >= BASE) a -= BASE; \ 37 } while (0) 38 # define MOD(a) \ 39 do { \ 40 CHOP(a); \ 41 MOD28(a); \ 42 } while (0) 43 # define MOD63(a) \ 44 do { /* this assumes a is not negative */ \ 45 z_off64_t tmp = a >> 32; \ 46 a &= 0xffffffffL; \ 47 a += (tmp << 8) - (tmp << 5) + tmp; \ 48 tmp = a >> 16; \ 49 a &= 0xffffL; \ 50 a += (tmp << 4) - tmp; \ 51 tmp = a >> 16; \ 52 a &= 0xffffL; \ 53 a += (tmp << 4) - tmp; \ 54 if (a >= BASE) a -= BASE; \ 55 } while (0) 56 #else 57 # define MOD(a) a %= BASE 58 # define MOD28(a) a %= BASE 59 # define MOD63(a) a %= BASE 60 #endif 61 62 /* ========================================================================= */ 63 uLong ZEXPORT adler32(adler, buf, len) 64 uLong adler; 65 const Bytef *buf; 66 uInt len; 67 { 68 unsigned long sum2; 69 unsigned n; 70 71 /* split Adler-32 into component sums */ 72 sum2 = (adler >> 16) & 0xffff; 73 adler &= 0xffff; 74 75 /* in case user likes doing a byte at a time, keep it fast */ 76 if (len == 1) { 77 adler += buf[0]; 78 if (adler >= BASE) 79 adler -= BASE; 80 sum2 += adler; 81 if (sum2 >= BASE) 82 sum2 -= BASE; 83 return adler | (sum2 << 16); 84 } 85 86 /* initial Adler-32 value (deferred check for len == 1 speed) */ 87 if (buf == Z_NULL) 88 return 1L; 89 90 /* in case short lengths are provided, keep it somewhat fast */ 91 if (len < 16) { 92 struct { 93 uLong a, b; 94 uInt c; 95 } x; 96 97 x.c = len; 98 99 while (len--) { 100 adler += *buf++; 101 sum2 += adler; 102 } 103 104 x.a = adler; 105 x.b = sum2; 106 zADDRND(x); 107 108 if (adler >= BASE) 109 adler -= BASE; 110 MOD28(sum2); /* only added so many BASE's */ 111 return adler | (sum2 << 16); 112 } 113 114 /* do length NMAX blocks -- requires just one modulo operation */ 115 while (len >= NMAX) { 116 len -= NMAX; 117 n = NMAX / 16; /* NMAX is divisible by 16 */ 118 do { 119 DO16(buf); /* 16 sums unrolled */ 120 buf += 16; 121 } while (--n); 122 MOD(adler); 123 MOD(sum2); 124 } 125 126 /* do remaining bytes (less than NMAX, still just one modulo) */ 127 if (len) { /* avoid modulos if none remaining */ 128 while (len >= 16) { 129 len -= 16; 130 DO16(buf); 131 buf += 16; 132 } 133 while (len--) { 134 adler += *buf++; 135 sum2 += adler; 136 } 137 MOD(adler); 138 MOD(sum2); 139 } 140 141 /* return recombined sums */ 142 adler |= sum2 << 16; 143 zADDRND(adler); 144 return (adler); 145 } 146