1 /* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2011, 2016 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6 #include "zutil.h" 7 8 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 9 10 #define BASE 65521U /* largest prime smaller than 65536 */ 11 #define NMAX 5552 12 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 13 14 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 15 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 16 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 17 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 18 #define DO16(buf) DO8(buf,0); DO8(buf,8); 19 20 /* use NO_DIVIDE if your processor does not do division in hardware -- 21 try it both ways to see which is faster */ 22 #ifdef NO_DIVIDE 23 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 24 (thank you to John Reiser for pointing this out) */ 25 # define CHOP(a) \ 26 do { \ 27 unsigned long tmp = a >> 16; \ 28 a &= 0xffffUL; \ 29 a += (tmp << 4) - tmp; \ 30 } while (0) 31 # define MOD28(a) \ 32 do { \ 33 CHOP(a); \ 34 if (a >= BASE) a -= BASE; \ 35 } while (0) 36 # define MOD(a) \ 37 do { \ 38 CHOP(a); \ 39 MOD28(a); \ 40 } while (0) 41 # define MOD63(a) \ 42 do { /* this assumes a is not negative */ \ 43 z_off64_t tmp = a >> 32; \ 44 a &= 0xffffffffL; \ 45 a += (tmp << 8) - (tmp << 5) + tmp; \ 46 tmp = a >> 16; \ 47 a &= 0xffffL; \ 48 a += (tmp << 4) - tmp; \ 49 tmp = a >> 16; \ 50 a &= 0xffffL; \ 51 a += (tmp << 4) - tmp; \ 52 if (a >= BASE) a -= BASE; \ 53 } while (0) 54 #else 55 # define MOD(a) a %= BASE 56 # define MOD28(a) a %= BASE 57 # define MOD63(a) a %= BASE 58 #endif 59 60 /* ========================================================================= */ 61 uLong ZEXPORT adler32_z(adler, buf, len) 62 uLong adler; 63 const Bytef *buf; 64 z_size_t 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 MOD28(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(adler, buf, len) 133 uLong adler; 134 const Bytef *buf; 135 uInt len; 136 { 137 return adler32_z(adler, buf, len); 138 } 139 140 /* ========================================================================= */ 141 local uLong adler32_combine_(adler1, adler2, len2) 142 uLong adler1; 143 uLong adler2; 144 z_off64_t len2; 145 { 146 unsigned long sum1; 147 unsigned long sum2; 148 unsigned rem; 149 150 /* for negative len, return invalid adler32 as a clue for debugging */ 151 if (len2 < 0) 152 return 0xffffffffUL; 153 154 /* the derivation of this formula is left as an exercise for the reader */ 155 MOD63(len2); /* assumes len2 >= 0 */ 156 rem = (unsigned)len2; 157 sum1 = adler1 & 0xffff; 158 sum2 = rem * sum1; 159 MOD(sum2); 160 sum1 += (adler2 & 0xffff) + BASE - 1; 161 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 162 if (sum1 >= BASE) sum1 -= BASE; 163 if (sum1 >= BASE) sum1 -= BASE; 164 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); 165 if (sum2 >= BASE) sum2 -= BASE; 166 return sum1 | (sum2 << 16); 167 } 168 169 /* ========================================================================= */ 170 uLong ZEXPORT adler32_combine(adler1, adler2, len2) 171 uLong adler1; 172 uLong adler2; 173 z_off_t len2; 174 { 175 return adler32_combine_(adler1, adler2, len2); 176 } 177 178 uLong ZEXPORT adler32_combine64(adler1, adler2, len2) 179 uLong adler1; 180 uLong adler2; 181 z_off64_t len2; 182 { 183 return adler32_combine_(adler1, adler2, len2); 184 } 185