Wei Chang Shen / DMemWin

Dependencies:   emwin_lib

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png/adler32.c@2:0e2ef1edf01b, 2016-06-02 (annotated)

Committer:
destinyXfate
Date:
Thu Jun 02 04:52:54 2016 +0000
Revision:
2:0e2ef1edf01b
;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
destinyXfate 2:0e2ef1edf01b 1 /* adler32.c -- compute the Adler-32 checksum of a data stream
destinyXfate 2:0e2ef1edf01b 2 * Copyright (C) 1995-2004 Mark Adler
destinyXfate 2:0e2ef1edf01b 3 * For conditions of distribution and use, see copyright notice in zlib.h
destinyXfate 2:0e2ef1edf01b 4 */
destinyXfate 2:0e2ef1edf01b 5
destinyXfate 2:0e2ef1edf01b 6 /* @(#) $Id$ */
destinyXfate 2:0e2ef1edf01b 7
destinyXfate 2:0e2ef1edf01b 8 #define ZLIB_INTERNAL
destinyXfate 2:0e2ef1edf01b 9 #include "zlib.h"
destinyXfate 2:0e2ef1edf01b 10
destinyXfate 2:0e2ef1edf01b 11 #define BASE 65521UL /* largest prime smaller than 65536 */
destinyXfate 2:0e2ef1edf01b 12 #define NMAX 5552
destinyXfate 2:0e2ef1edf01b 13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
destinyXfate 2:0e2ef1edf01b 14
destinyXfate 2:0e2ef1edf01b 15 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
destinyXfate 2:0e2ef1edf01b 16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
destinyXfate 2:0e2ef1edf01b 17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
destinyXfate 2:0e2ef1edf01b 18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
destinyXfate 2:0e2ef1edf01b 19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
destinyXfate 2:0e2ef1edf01b 20
destinyXfate 2:0e2ef1edf01b 21 /* use NO_DIVIDE if your processor does not do division in hardware */
destinyXfate 2:0e2ef1edf01b 22 #ifdef NO_DIVIDE
destinyXfate 2:0e2ef1edf01b 23 # define MOD(a) \
destinyXfate 2:0e2ef1edf01b 24 do { \
destinyXfate 2:0e2ef1edf01b 25 if (a >= (BASE << 16)) a -= (BASE << 16); \
destinyXfate 2:0e2ef1edf01b 26 if (a >= (BASE << 15)) a -= (BASE << 15); \
destinyXfate 2:0e2ef1edf01b 27 if (a >= (BASE << 14)) a -= (BASE << 14); \
destinyXfate 2:0e2ef1edf01b 28 if (a >= (BASE << 13)) a -= (BASE << 13); \
destinyXfate 2:0e2ef1edf01b 29 if (a >= (BASE << 12)) a -= (BASE << 12); \
destinyXfate 2:0e2ef1edf01b 30 if (a >= (BASE << 11)) a -= (BASE << 11); \
destinyXfate 2:0e2ef1edf01b 31 if (a >= (BASE << 10)) a -= (BASE << 10); \
destinyXfate 2:0e2ef1edf01b 32 if (a >= (BASE << 9)) a -= (BASE << 9); \
destinyXfate 2:0e2ef1edf01b 33 if (a >= (BASE << 8)) a -= (BASE << 8); \
destinyXfate 2:0e2ef1edf01b 34 if (a >= (BASE << 7)) a -= (BASE << 7); \
destinyXfate 2:0e2ef1edf01b 35 if (a >= (BASE << 6)) a -= (BASE << 6); \
destinyXfate 2:0e2ef1edf01b 36 if (a >= (BASE << 5)) a -= (BASE << 5); \
destinyXfate 2:0e2ef1edf01b 37 if (a >= (BASE << 4)) a -= (BASE << 4); \
destinyXfate 2:0e2ef1edf01b 38 if (a >= (BASE << 3)) a -= (BASE << 3); \
destinyXfate 2:0e2ef1edf01b 39 if (a >= (BASE << 2)) a -= (BASE << 2); \
destinyXfate 2:0e2ef1edf01b 40 if (a >= (BASE << 1)) a -= (BASE << 1); \
destinyXfate 2:0e2ef1edf01b 41 if (a >= BASE) a -= BASE; \
destinyXfate 2:0e2ef1edf01b 42 } while (0)
destinyXfate 2:0e2ef1edf01b 43 # define MOD4(a) \
destinyXfate 2:0e2ef1edf01b 44 do { \
destinyXfate 2:0e2ef1edf01b 45 if (a >= (BASE << 4)) a -= (BASE << 4); \
destinyXfate 2:0e2ef1edf01b 46 if (a >= (BASE << 3)) a -= (BASE << 3); \
destinyXfate 2:0e2ef1edf01b 47 if (a >= (BASE << 2)) a -= (BASE << 2); \
destinyXfate 2:0e2ef1edf01b 48 if (a >= (BASE << 1)) a -= (BASE << 1); \
destinyXfate 2:0e2ef1edf01b 49 if (a >= BASE) a -= BASE; \
destinyXfate 2:0e2ef1edf01b 50 } while (0)
destinyXfate 2:0e2ef1edf01b 51 #else
destinyXfate 2:0e2ef1edf01b 52 # define MOD(a) a %= BASE
destinyXfate 2:0e2ef1edf01b 53 # define MOD4(a) a %= BASE
destinyXfate 2:0e2ef1edf01b 54 #endif
destinyXfate 2:0e2ef1edf01b 55
destinyXfate 2:0e2ef1edf01b 56 /* ========================================================================= */
destinyXfate 2:0e2ef1edf01b 57 uLong ZEXPORT adler32(adler, buf, len)
destinyXfate 2:0e2ef1edf01b 58 uLong adler;
destinyXfate 2:0e2ef1edf01b 59 const Bytef *buf;
destinyXfate 2:0e2ef1edf01b 60 uInt len;
destinyXfate 2:0e2ef1edf01b 61 {
destinyXfate 2:0e2ef1edf01b 62 unsigned long sum2;
destinyXfate 2:0e2ef1edf01b 63 unsigned n;
destinyXfate 2:0e2ef1edf01b 64
destinyXfate 2:0e2ef1edf01b 65 /* split Adler-32 into component sums */
destinyXfate 2:0e2ef1edf01b 66 sum2 = (adler >> 16) & 0xffff;
destinyXfate 2:0e2ef1edf01b 67 adler &= 0xffff;
destinyXfate 2:0e2ef1edf01b 68
destinyXfate 2:0e2ef1edf01b 69 /* in case user likes doing a byte at a time, keep it fast */
destinyXfate 2:0e2ef1edf01b 70 if (len == 1) {
destinyXfate 2:0e2ef1edf01b 71 adler += buf[0];
destinyXfate 2:0e2ef1edf01b 72 if (adler >= BASE)
destinyXfate 2:0e2ef1edf01b 73 adler -= BASE;
destinyXfate 2:0e2ef1edf01b 74 sum2 += adler;
destinyXfate 2:0e2ef1edf01b 75 if (sum2 >= BASE)
destinyXfate 2:0e2ef1edf01b 76 sum2 -= BASE;
destinyXfate 2:0e2ef1edf01b 77 return adler | (sum2 << 16);
destinyXfate 2:0e2ef1edf01b 78 }
destinyXfate 2:0e2ef1edf01b 79
destinyXfate 2:0e2ef1edf01b 80 /* initial Adler-32 value (deferred check for len == 1 speed) */
destinyXfate 2:0e2ef1edf01b 81 if (buf == Z_NULL)
destinyXfate 2:0e2ef1edf01b 82 return 1L;
destinyXfate 2:0e2ef1edf01b 83
destinyXfate 2:0e2ef1edf01b 84 /* in case short lengths are provided, keep it somewhat fast */
destinyXfate 2:0e2ef1edf01b 85 if (len < 16) {
destinyXfate 2:0e2ef1edf01b 86 while (len--) {
destinyXfate 2:0e2ef1edf01b 87 adler += *buf++;
destinyXfate 2:0e2ef1edf01b 88 sum2 += adler;
destinyXfate 2:0e2ef1edf01b 89 }
destinyXfate 2:0e2ef1edf01b 90 if (adler >= BASE)
destinyXfate 2:0e2ef1edf01b 91 adler -= BASE;
destinyXfate 2:0e2ef1edf01b 92 MOD4(sum2); /* only added so many BASE's */
destinyXfate 2:0e2ef1edf01b 93 return adler | (sum2 << 16);
destinyXfate 2:0e2ef1edf01b 94 }
destinyXfate 2:0e2ef1edf01b 95
destinyXfate 2:0e2ef1edf01b 96 /* do length NMAX blocks -- requires just one modulo operation */
destinyXfate 2:0e2ef1edf01b 97 while (len >= NMAX) {
destinyXfate 2:0e2ef1edf01b 98 len -= NMAX;
destinyXfate 2:0e2ef1edf01b 99 n = NMAX / 16; /* NMAX is divisible by 16 */
destinyXfate 2:0e2ef1edf01b 100 do {
destinyXfate 2:0e2ef1edf01b 101 DO16(buf); /* 16 sums unrolled */
destinyXfate 2:0e2ef1edf01b 102 buf += 16;
destinyXfate 2:0e2ef1edf01b 103 } while (--n);
destinyXfate 2:0e2ef1edf01b 104 MOD(adler);
destinyXfate 2:0e2ef1edf01b 105 MOD(sum2);
destinyXfate 2:0e2ef1edf01b 106 }
destinyXfate 2:0e2ef1edf01b 107
destinyXfate 2:0e2ef1edf01b 108 /* do remaining bytes (less than NMAX, still just one modulo) */
destinyXfate 2:0e2ef1edf01b 109 if (len) { /* avoid modulos if none remaining */
destinyXfate 2:0e2ef1edf01b 110 while (len >= 16) {
destinyXfate 2:0e2ef1edf01b 111 len -= 16;
destinyXfate 2:0e2ef1edf01b 112 DO16(buf);
destinyXfate 2:0e2ef1edf01b 113 buf += 16;
destinyXfate 2:0e2ef1edf01b 114 }
destinyXfate 2:0e2ef1edf01b 115 while (len--) {
destinyXfate 2:0e2ef1edf01b 116 adler += *buf++;
destinyXfate 2:0e2ef1edf01b 117 sum2 += adler;
destinyXfate 2:0e2ef1edf01b 118 }
destinyXfate 2:0e2ef1edf01b 119 MOD(adler);
destinyXfate 2:0e2ef1edf01b 120 MOD(sum2);
destinyXfate 2:0e2ef1edf01b 121 }
destinyXfate 2:0e2ef1edf01b 122
destinyXfate 2:0e2ef1edf01b 123 /* return recombined sums */
destinyXfate 2:0e2ef1edf01b 124 return adler | (sum2 << 16);
destinyXfate 2:0e2ef1edf01b 125 }
destinyXfate 2:0e2ef1edf01b 126
destinyXfate 2:0e2ef1edf01b 127 /* ========================================================================= */
destinyXfate 2:0e2ef1edf01b 128 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
destinyXfate 2:0e2ef1edf01b 129 uLong adler1;
destinyXfate 2:0e2ef1edf01b 130 uLong adler2;
destinyXfate 2:0e2ef1edf01b 131 z_off_t len2;
destinyXfate 2:0e2ef1edf01b 132 {
destinyXfate 2:0e2ef1edf01b 133 unsigned long sum1;
destinyXfate 2:0e2ef1edf01b 134 unsigned long sum2;
destinyXfate 2:0e2ef1edf01b 135 unsigned rem;
destinyXfate 2:0e2ef1edf01b 136
destinyXfate 2:0e2ef1edf01b 137 /* the derivation of this formula is left as an exercise for the reader */
destinyXfate 2:0e2ef1edf01b 138 rem = (unsigned)(len2 % BASE);
destinyXfate 2:0e2ef1edf01b 139 sum1 = adler1 & 0xffff;
destinyXfate 2:0e2ef1edf01b 140 sum2 = rem * sum1;
destinyXfate 2:0e2ef1edf01b 141 MOD(sum2);
destinyXfate 2:0e2ef1edf01b 142 sum1 += (adler2 & 0xffff) + BASE - 1;
destinyXfate 2:0e2ef1edf01b 143 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
destinyXfate 2:0e2ef1edf01b 144 if (sum1 > BASE) sum1 -= BASE;
destinyXfate 2:0e2ef1edf01b 145 if (sum1 > BASE) sum1 -= BASE;
destinyXfate 2:0e2ef1edf01b 146 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
destinyXfate 2:0e2ef1edf01b 147 if (sum2 > BASE) sum2 -= BASE;
destinyXfate 2:0e2ef1edf01b 148 return sum1 | (sum2 << 16);
destinyXfate 2:0e2ef1edf01b 149 }
destinyXfate 2:0e2ef1edf01b 150