1 | /* adler32.c -- compute the Adler-32 checksum of a data stream |
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2 | * Copyright (C) 1995-2007 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 | /* @(#) $Id$ */ |
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7 | |
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8 | #include "zutil.h" |
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9 | |
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10 | #define local static |
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11 | |
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12 | local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2); |
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13 | |
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14 | #define BASE 65521UL /* largest prime smaller than 65536 */ |
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15 | #define NMAX 5552 |
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16 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ |
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17 | |
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18 | #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} |
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19 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); |
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20 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); |
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21 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); |
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22 | #define DO16(buf) DO8(buf,0); DO8(buf,8); |
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23 | |
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24 | /* use NO_DIVIDE if your processor does not do division in hardware */ |
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25 | #ifdef NO_DIVIDE |
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26 | # define MOD(a) \ |
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27 | do { \ |
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28 | if (a >= (BASE << 16)) a -= (BASE << 16); \ |
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29 | if (a >= (BASE << 15)) a -= (BASE << 15); \ |
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30 | if (a >= (BASE << 14)) a -= (BASE << 14); \ |
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31 | if (a >= (BASE << 13)) a -= (BASE << 13); \ |
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32 | if (a >= (BASE << 12)) a -= (BASE << 12); \ |
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33 | if (a >= (BASE << 11)) a -= (BASE << 11); \ |
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34 | if (a >= (BASE << 10)) a -= (BASE << 10); \ |
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35 | if (a >= (BASE << 9)) a -= (BASE << 9); \ |
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36 | if (a >= (BASE << 8)) a -= (BASE << 8); \ |
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37 | if (a >= (BASE << 7)) a -= (BASE << 7); \ |
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38 | if (a >= (BASE << 6)) a -= (BASE << 6); \ |
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39 | if (a >= (BASE << 5)) a -= (BASE << 5); \ |
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40 | if (a >= (BASE << 4)) a -= (BASE << 4); \ |
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41 | if (a >= (BASE << 3)) a -= (BASE << 3); \ |
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42 | if (a >= (BASE << 2)) a -= (BASE << 2); \ |
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43 | if (a >= (BASE << 1)) a -= (BASE << 1); \ |
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44 | if (a >= BASE) a -= BASE; \ |
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45 | } while (0) |
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46 | # define MOD4(a) \ |
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47 | do { \ |
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48 | if (a >= (BASE << 4)) a -= (BASE << 4); \ |
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49 | if (a >= (BASE << 3)) a -= (BASE << 3); \ |
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50 | if (a >= (BASE << 2)) a -= (BASE << 2); \ |
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51 | if (a >= (BASE << 1)) a -= (BASE << 1); \ |
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52 | if (a >= BASE) a -= BASE; \ |
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53 | } while (0) |
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54 | #else |
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55 | # define MOD(a) a %= BASE |
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56 | # define MOD4(a) a %= BASE |
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57 | #endif |
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58 | |
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59 | /* ========================================================================= */ |
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60 | uLong ZEXPORT adler32(adler, buf, len) |
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61 | uLong adler; |
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62 | const Bytef *buf; |
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63 | uInt len; |
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64 | { |
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65 | unsigned long sum2; |
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66 | unsigned n; |
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67 | |
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68 | /* split Adler-32 into component sums */ |
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69 | sum2 = (adler >> 16) & 0xffff; |
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70 | adler &= 0xffff; |
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71 | |
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72 | /* in case user likes doing a byte at a time, keep it fast */ |
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73 | if (len == 1) { |
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74 | adler += buf[0]; |
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75 | if (adler >= BASE) |
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76 | adler -= BASE; |
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77 | sum2 += adler; |
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78 | if (sum2 >= BASE) |
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79 | sum2 -= BASE; |
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80 | return adler | (sum2 << 16); |
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81 | } |
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82 | |
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83 | /* initial Adler-32 value (deferred check for len == 1 speed) */ |
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84 | if (buf == Z_NULL) |
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85 | return 1L; |
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86 | |
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87 | /* in case short lengths are provided, keep it somewhat fast */ |
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88 | if (len < 16) { |
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89 | while (len--) { |
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90 | adler += *buf++; |
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91 | sum2 += adler; |
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92 | } |
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93 | if (adler >= BASE) |
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94 | adler -= BASE; |
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95 | MOD4(sum2); /* only added so many BASE's */ |
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96 | return adler | (sum2 << 16); |
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97 | } |
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98 | |
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99 | /* do length NMAX blocks -- requires just one modulo operation */ |
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100 | while (len >= NMAX) { |
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101 | len -= NMAX; |
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102 | n = NMAX / 16; /* NMAX is divisible by 16 */ |
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103 | do { |
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104 | DO16(buf); /* 16 sums unrolled */ |
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105 | buf += 16; |
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106 | } while (--n); |
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107 | MOD(adler); |
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108 | MOD(sum2); |
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109 | } |
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110 | |
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111 | /* do remaining bytes (less than NMAX, still just one modulo) */ |
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112 | if (len) { /* avoid modulos if none remaining */ |
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113 | while (len >= 16) { |
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114 | len -= 16; |
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115 | DO16(buf); |
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116 | buf += 16; |
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117 | } |
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118 | while (len--) { |
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119 | adler += *buf++; |
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120 | sum2 += adler; |
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121 | } |
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122 | MOD(adler); |
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123 | MOD(sum2); |
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124 | } |
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125 | |
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126 | /* return recombined sums */ |
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127 | return adler | (sum2 << 16); |
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128 | } |
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129 | |
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130 | /* ========================================================================= */ |
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131 | local uLong adler32_combine_(adler1, adler2, len2) |
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132 | uLong adler1; |
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133 | uLong adler2; |
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134 | z_off64_t len2; |
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135 | { |
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136 | unsigned long sum1; |
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137 | unsigned long sum2; |
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138 | unsigned rem; |
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139 | |
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140 | /* the derivation of this formula is left as an exercise for the reader */ |
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141 | rem = (unsigned)(len2 % BASE); |
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142 | sum1 = adler1 & 0xffff; |
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143 | sum2 = rem * sum1; |
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144 | MOD(sum2); |
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145 | sum1 += (adler2 & 0xffff) + BASE - 1; |
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146 | sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; |
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147 | if (sum1 >= BASE) sum1 -= BASE; |
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148 | if (sum1 >= BASE) sum1 -= BASE; |
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149 | if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1); |
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150 | if (sum2 >= BASE) sum2 -= BASE; |
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151 | return sum1 | (sum2 << 16); |
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152 | } |
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153 | |
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154 | /* ========================================================================= */ |
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155 | uLong ZEXPORT adler32_combine(adler1, adler2, len2) |
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156 | uLong adler1; |
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157 | uLong adler2; |
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158 | z_off_t len2; |
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159 | { |
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160 | return adler32_combine_(adler1, adler2, len2); |
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161 | } |
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162 | |
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163 | uLong ZEXPORT adler32_combine64(adler1, adler2, len2) |
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164 | uLong adler1; |
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165 | uLong adler2; |
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166 | z_off64_t len2; |
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167 | { |
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168 | return adler32_combine_(adler1, adler2, len2); |
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169 | } |
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