1 /* $OpenBSD: adler32.c,v 1.11 2021/07/04 14:24:49 tb Exp $ */ 2 /* adler32.c -- compute the Adler-32 checksum of a data stream 3 * Copyright (C) 1995-2011, 2016 Mark Adler 4 * For conditions of distribution and use, see copyright notice in zlib.h 5 */ 6 7 #include "zutil.h" 8 9 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 10 11 #define BASE 65521U /* 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 try it both ways to see which is faster */ 23 #ifdef NO_DIVIDE 24 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 25 (thank you to John Reiser for pointing this out) */ 26 # define CHOP(a) \ 27 do { \ 28 unsigned long tmp = a >> 16; \ 29 a &= 0xffffUL; \ 30 a += (tmp << 4) - tmp; \ 31 } while (0) 32 # define MOD28(a) \ 33 do { \ 34 CHOP(a); \ 35 if (a >= BASE) a -= BASE; \ 36 } while (0) 37 # define MOD(a) \ 38 do { \ 39 CHOP(a); \ 40 MOD28(a); \ 41 } while (0) 42 # define MOD63(a) \ 43 do { /* this assumes a is not negative */ \ 44 z_off64_t tmp = a >> 32; \ 45 a &= 0xffffffffL; \ 46 a += (tmp << 8) - (tmp << 5) + tmp; \ 47 tmp = a >> 16; \ 48 a &= 0xffffL; \ 49 a += (tmp << 4) - tmp; \ 50 tmp = a >> 16; \ 51 a &= 0xffffL; \ 52 a += (tmp << 4) - tmp; \ 53 if (a >= BASE) a -= BASE; \ 54 } while (0) 55 #else 56 # define MOD(a) a %= BASE 57 # define MOD28(a) a %= BASE 58 # define MOD63(a) a %= BASE 59 #endif 60 61 /* ========================================================================= */ 62 uLong ZEXPORT adler32_z(adler, buf, len) 63 uLong adler; 64 const Bytef *buf; 65 z_size_t len; 66 { 67 unsigned long sum2; 68 unsigned n; 69 70 /* split Adler-32 into component sums */ 71 sum2 = (adler >> 16) & 0xffff; 72 adler &= 0xffff; 73 74 /* in case user likes doing a byte at a time, keep it fast */ 75 if (len == 1) { 76 adler += buf[0]; 77 if (adler >= BASE) 78 adler -= BASE; 79 sum2 += adler; 80 if (sum2 >= BASE) 81 sum2 -= BASE; 82 return adler | (sum2 << 16); 83 } 84 85 /* initial Adler-32 value (deferred check for len == 1 speed) */ 86 if (buf == Z_NULL) 87 return 1L; 88 89 /* in case short lengths are provided, keep it somewhat fast */ 90 if (len < 16) { 91 while (len--) { 92 adler += *buf++; 93 sum2 += adler; 94 } 95 if (adler >= BASE) 96 adler -= BASE; 97 MOD28(sum2); /* only added so many BASE's */ 98 return adler | (sum2 << 16); 99 } 100 101 /* do length NMAX blocks -- requires just one modulo operation */ 102 while (len >= NMAX) { 103 len -= NMAX; 104 n = NMAX / 16; /* NMAX is divisible by 16 */ 105 do { 106 DO16(buf); /* 16 sums unrolled */ 107 buf += 16; 108 } while (--n); 109 MOD(adler); 110 MOD(sum2); 111 } 112 113 /* do remaining bytes (less than NMAX, still just one modulo) */ 114 if (len) { /* avoid modulos if none remaining */ 115 while (len >= 16) { 116 len -= 16; 117 DO16(buf); 118 buf += 16; 119 } 120 while (len--) { 121 adler += *buf++; 122 sum2 += adler; 123 } 124 MOD(adler); 125 MOD(sum2); 126 } 127 128 /* return recombined sums */ 129 return adler | (sum2 << 16); 130 } 131 132 /* ========================================================================= */ 133 uLong ZEXPORT adler32(adler, buf, len) 134 uLong adler; 135 const Bytef *buf; 136 uInt len; 137 { 138 return adler32_z(adler, buf, len); 139 } 140 141 /* ========================================================================= */ 142 local uLong adler32_combine_(adler1, adler2, len2) 143 uLong adler1; 144 uLong adler2; 145 z_off64_t len2; 146 { 147 unsigned long sum1; 148 unsigned long sum2; 149 unsigned rem; 150 151 /* for negative len, return invalid adler32 as a clue for debugging */ 152 if (len2 < 0) 153 return 0xffffffffUL; 154 155 /* the derivation of this formula is left as an exercise for the reader */ 156 MOD63(len2); /* assumes len2 >= 0 */ 157 rem = (unsigned)len2; 158 sum1 = adler1 & 0xffff; 159 sum2 = rem * sum1; 160 MOD(sum2); 161 sum1 += (adler2 & 0xffff) + BASE - 1; 162 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 163 if (sum1 >= BASE) sum1 -= BASE; 164 if (sum1 >= BASE) sum1 -= BASE; 165 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); 166 if (sum2 >= BASE) sum2 -= BASE; 167 return sum1 | (sum2 << 16); 168 } 169 170 /* ========================================================================= */ 171 uLong ZEXPORT adler32_combine(adler1, adler2, len2) 172 uLong adler1; 173 uLong adler2; 174 z_off_t len2; 175 { 176 return adler32_combine_(adler1, adler2, len2); 177 } 178 179 uLong ZEXPORT adler32_combine64(adler1, adler2, len2) 180 uLong adler1; 181 uLong adler2; 182 z_off64_t len2; 183 { 184 return adler32_combine_(adler1, adler2, len2); 185 } 186