1 // SPDX-License-Identifier: Zlib 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 /* @(#) $Id$ */ 8 9 #include "zutil.h" 10 11 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 12 13 #define BASE 65521U /* largest prime smaller than 65536 */ 14 #define NMAX 5552 15 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 16 17 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 18 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 19 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 20 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 21 #define DO16(buf) DO8(buf,0); DO8(buf,8); 22 23 /* use NO_DIVIDE if your processor does not do division in hardware -- 24 try it both ways to see which is faster */ 25 #ifdef NO_DIVIDE 26 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 27 (thank you to John Reiser for pointing this out) */ 28 # define CHOP(a) \ 29 do { \ 30 unsigned long tmp = a >> 16; \ 31 a &= 0xffffUL; \ 32 a += (tmp << 4) - tmp; \ 33 } while (0) 34 # define MOD28(a) \ 35 do { \ 36 CHOP(a); \ 37 if (a >= BASE) a -= BASE; \ 38 } while (0) 39 # define MOD(a) \ 40 do { \ 41 CHOP(a); \ 42 MOD28(a); \ 43 } while (0) 44 # define MOD63(a) \ 45 do { /* this assumes a is not negative */ \ 46 z_off64_t tmp = a >> 32; \ 47 a &= 0xffffffffL; \ 48 a += (tmp << 8) - (tmp << 5) + tmp; \ 49 tmp = a >> 16; \ 50 a &= 0xffffL; \ 51 a += (tmp << 4) - tmp; \ 52 tmp = a >> 16; \ 53 a &= 0xffffL; \ 54 a += (tmp << 4) - tmp; \ 55 if (a >= BASE) a -= BASE; \ 56 } while (0) 57 #else 58 # define MOD(a) a %= BASE 59 # define MOD28(a) a %= BASE 60 # define MOD63(a) a %= BASE 61 #endif 62 63 /* ========================================================================= */ 64 uLong ZEXPORT adler32_z(adler, buf, len) 65 uLong adler; 66 const Bytef *buf; 67 z_size_t len; 68 { 69 unsigned long sum2; 70 unsigned n; 71 72 /* split Adler-32 into component sums */ 73 sum2 = (adler >> 16) & 0xffff; 74 adler &= 0xffff; 75 76 /* in case user likes doing a byte at a time, keep it fast */ 77 if (len == 1) { 78 adler += buf[0]; 79 if (adler >= BASE) 80 adler -= BASE; 81 sum2 += adler; 82 if (sum2 >= BASE) 83 sum2 -= BASE; 84 return adler | (sum2 << 16); 85 } 86 87 /* initial Adler-32 value (deferred check for len == 1 speed) */ 88 if (buf == Z_NULL) 89 return 1L; 90 91 /* in case short lengths are provided, keep it somewhat fast */ 92 if (len < 16) { 93 while (len--) { 94 adler += *buf++; 95 sum2 += adler; 96 } 97 if (adler >= BASE) 98 adler -= BASE; 99 MOD28(sum2); /* only added so many BASE's */ 100 return adler | (sum2 << 16); 101 } 102 103 /* do length NMAX blocks -- requires just one modulo operation */ 104 while (len >= NMAX) { 105 len -= NMAX; 106 n = NMAX / 16; /* NMAX is divisible by 16 */ 107 do { 108 DO16(buf); /* 16 sums unrolled */ 109 buf += 16; 110 } while (--n); 111 MOD(adler); 112 MOD(sum2); 113 } 114 115 /* do remaining bytes (less than NMAX, still just one modulo) */ 116 if (len) { /* avoid modulos if none remaining */ 117 while (len >= 16) { 118 len -= 16; 119 DO16(buf); 120 buf += 16; 121 } 122 while (len--) { 123 adler += *buf++; 124 sum2 += adler; 125 } 126 MOD(adler); 127 MOD(sum2); 128 } 129 130 /* return recombined sums */ 131 return adler | (sum2 << 16); 132 } 133 134 /* ========================================================================= */ 135 uLong ZEXPORT adler32(adler, buf, len) 136 uLong adler; 137 const Bytef *buf; 138 uInt len; 139 { 140 return adler32_z(adler, buf, len); 141 } 142 143 /* ========================================================================= */ 144 local uLong adler32_combine_(adler1, adler2, len2) 145 uLong adler1; 146 uLong adler2; 147 z_off64_t len2; 148 { 149 unsigned long sum1; 150 unsigned long sum2; 151 unsigned rem; 152 153 /* for negative len, return invalid adler32 as a clue for debugging */ 154 if (len2 < 0) 155 return 0xffffffffUL; 156 157 /* the derivation of this formula is left as an exercise for the reader */ 158 MOD63(len2); /* assumes len2 >= 0 */ 159 rem = (unsigned)len2; 160 sum1 = adler1 & 0xffff; 161 sum2 = rem * sum1; 162 MOD(sum2); 163 sum1 += (adler2 & 0xffff) + BASE - 1; 164 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 165 if (sum1 >= BASE) sum1 -= BASE; 166 if (sum1 >= BASE) sum1 -= BASE; 167 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); 168 if (sum2 >= BASE) sum2 -= BASE; 169 return sum1 | (sum2 << 16); 170 } 171 172 /* ========================================================================= */ 173 uLong ZEXPORT adler32_combine(adler1, adler2, len2) 174 uLong adler1; 175 uLong adler2; 176 z_off_t len2; 177 { 178 return adler32_combine_(adler1, adler2, len2); 179 } 180 181 uLong ZEXPORT adler32_combine64(adler1, adler2, len2) 182 uLong adler1; 183 uLong adler2; 184 z_off64_t len2; 185 { 186 return adler32_combine_(adler1, adler2, len2); 187 } 188