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