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annotate deps/Platinum/ThirdParty/Neptune/ThirdParty/zlib-1.2.3/adler32.c @ 0:3425707ddbf6

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Initial import (hopefully this mercurial stuff works...)
author fraserofthenight
date Mon, 06 Jul 2009 08:06:28 -0700
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream
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2 * Copyright (C) 1995-2004 Mark Adler
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3 * For conditions of distribution and use, see copyright notice in zlib.h
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4 */
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5
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6 /* @(#) $Id: adler32.c 87 2008-08-15 19:03:36Z bok $ */
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7
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8 #define ZLIB_INTERNAL
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9 #include "zlib.h"
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10
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11 #define BASE 65521UL /* largest prime smaller than 65536 */
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12 #define NMAX 5552
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13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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14
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15 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
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16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
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17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
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18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
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19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
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20
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21 /* use NO_DIVIDE if your processor does not do division in hardware */
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22 #ifdef NO_DIVIDE
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23 # define MOD(a) \
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24 do { \
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25 if (a >= (BASE << 16)) a -= (BASE << 16); \
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26 if (a >= (BASE << 15)) a -= (BASE << 15); \
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27 if (a >= (BASE << 14)) a -= (BASE << 14); \
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28 if (a >= (BASE << 13)) a -= (BASE << 13); \
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29 if (a >= (BASE << 12)) a -= (BASE << 12); \
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30 if (a >= (BASE << 11)) a -= (BASE << 11); \
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31 if (a >= (BASE << 10)) a -= (BASE << 10); \
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32 if (a >= (BASE << 9)) a -= (BASE << 9); \
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33 if (a >= (BASE << 8)) a -= (BASE << 8); \
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34 if (a >= (BASE << 7)) a -= (BASE << 7); \
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35 if (a >= (BASE << 6)) a -= (BASE << 6); \
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36 if (a >= (BASE << 5)) a -= (BASE << 5); \
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37 if (a >= (BASE << 4)) a -= (BASE << 4); \
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38 if (a >= (BASE << 3)) a -= (BASE << 3); \
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39 if (a >= (BASE << 2)) a -= (BASE << 2); \
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40 if (a >= (BASE << 1)) a -= (BASE << 1); \
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41 if (a >= BASE) a -= BASE; \
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42 } while (0)
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43 # define MOD4(a) \
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44 do { \
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45 if (a >= (BASE << 4)) a -= (BASE << 4); \
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46 if (a >= (BASE << 3)) a -= (BASE << 3); \
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47 if (a >= (BASE << 2)) a -= (BASE << 2); \
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48 if (a >= (BASE << 1)) a -= (BASE << 1); \
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49 if (a >= BASE) a -= BASE; \
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50 } while (0)
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51 #else
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52 # define MOD(a) a %= BASE
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53 # define MOD4(a) a %= BASE
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54 #endif
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55
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56 /* ========================================================================= */
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57 uLong ZEXPORT adler32(adler, buf, len)
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58 uLong adler;
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59 const Bytef *buf;
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60 uInt len;
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61 {
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62 unsigned long sum2;
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63 unsigned n;
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64
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65 /* split Adler-32 into component sums */
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66 sum2 = (adler >> 16) & 0xffff;
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67 adler &= 0xffff;
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68
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69 /* in case user likes doing a byte at a time, keep it fast */
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70 if (len == 1) {
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71 adler += buf[0];
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72 if (adler >= BASE)
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73 adler -= BASE;
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74 sum2 += adler;
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75 if (sum2 >= BASE)
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76 sum2 -= BASE;
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77 return adler | (sum2 << 16);
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78 }
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79
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80 /* initial Adler-32 value (deferred check for len == 1 speed) */
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81 if (buf == Z_NULL)
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82 return 1L;
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83
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84 /* in case short lengths are provided, keep it somewhat fast */
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85 if (len < 16) {
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86 while (len--) {
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87 adler += *buf++;
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88 sum2 += adler;
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89 }
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90 if (adler >= BASE)
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91 adler -= BASE;
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92 MOD4(sum2); /* only added so many BASE's */
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93 return adler | (sum2 << 16);
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94 }
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95
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96 /* do length NMAX blocks -- requires just one modulo operation */
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97 while (len >= NMAX) {
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98 len -= NMAX;
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99 n = NMAX / 16; /* NMAX is divisible by 16 */
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100 do {
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101 DO16(buf); /* 16 sums unrolled */
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102 buf += 16;
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103 } while (--n);
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104 MOD(adler);
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105 MOD(sum2);
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106 }
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107
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108 /* do remaining bytes (less than NMAX, still just one modulo) */
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109 if (len) { /* avoid modulos if none remaining */
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110 while (len >= 16) {
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111 len -= 16;
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112 DO16(buf);
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113 buf += 16;
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114 }
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115 while (len--) {
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116 adler += *buf++;
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117 sum2 += adler;
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118 }
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119 MOD(adler);
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120 MOD(sum2);
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121 }
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122
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123 /* return recombined sums */
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124 return adler | (sum2 << 16);
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125 }
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126
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127 /* ========================================================================= */
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128 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
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129 uLong adler1;
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130 uLong adler2;
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131 z_off_t len2;
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132 {
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133 unsigned long sum1;
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134 unsigned long sum2;
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135 unsigned rem;
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136
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137 /* the derivation of this formula is left as an exercise for the reader */
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138 rem = (unsigned)(len2 % BASE);
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139 sum1 = adler1 & 0xffff;
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140 sum2 = rem * sum1;
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141 MOD(sum2);
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142 sum1 += (adler2 & 0xffff) + BASE - 1;
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143 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
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144 if (sum1 > BASE) sum1 -= BASE;
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145 if (sum1 > BASE) sum1 -= BASE;
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146 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
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147 if (sum2 > BASE) sum2 -= BASE;
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148 return sum1 | (sum2 << 16);
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149 }