1 | /* adler32.c -- compute the Adler-32 checksum of a data stream
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2 | * Copyright (C) 1995-2011, 2016 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 BASE 65521U /* largest prime smaller than 65536 */
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11 | #define NMAX 5552
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12 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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13 |
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14 | #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
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15 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
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16 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
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17 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
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18 | #define DO16(buf) DO8(buf,0); DO8(buf,8);
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19 |
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20 | /* use NO_DIVIDE if your processor does not do division in hardware --
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21 | try it both ways to see which is faster */
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22 | #ifdef NO_DIVIDE
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23 | /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
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24 | (thank you to John Reiser for pointing this out) */
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25 | # define CHOP(a) \
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26 | do { \
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27 | unsigned long tmp = a >> 16; \
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28 | a &= 0xffffUL; \
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29 | a += (tmp << 4) - tmp; \
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30 | } while (0)
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31 | # define MOD28(a) \
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32 | do { \
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33 | CHOP(a); \
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34 | if (a >= BASE) a -= BASE; \
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35 | } while (0)
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36 | # define MOD(a) \
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37 | do { \
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38 | CHOP(a); \
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39 | MOD28(a); \
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40 | } while (0)
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41 | # define MOD63(a) \
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42 | do { /* this assumes a is not negative */ \
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43 | z_off64_t tmp = a >> 32; \
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44 | a &= 0xffffffffL; \
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45 | a += (tmp << 8) - (tmp << 5) + tmp; \
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46 | tmp = a >> 16; \
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47 | a &= 0xffffL; \
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48 | a += (tmp << 4) - tmp; \
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49 | tmp = a >> 16; \
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50 | a &= 0xffffL; \
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51 | a += (tmp << 4) - tmp; \
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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 MOD28(a) a %= BASE
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57 | # define MOD63(a) a %= BASE
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58 | #endif
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59 |
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60 | /* ========================================================================= */
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61 | uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len) {
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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 | MOD28(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(uLong adler, const Bytef *buf, uInt len) {
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129 | return adler32_z(adler, buf, len);
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130 | }
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131 |
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132 | /* ========================================================================= */
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133 | local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2) {
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134 | unsigned long sum1;
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135 | unsigned long sum2;
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136 | unsigned rem;
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137 |
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138 | /* for negative len, return invalid adler32 as a clue for debugging */
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139 | if (len2 < 0)
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140 | return 0xffffffffUL;
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141 |
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142 | /* the derivation of this formula is left as an exercise for the reader */
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143 | MOD63(len2); /* assumes len2 >= 0 */
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144 | rem = (unsigned)len2;
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145 | sum1 = adler1 & 0xffff;
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146 | sum2 = rem * sum1;
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147 | MOD(sum2);
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148 | sum1 += (adler2 & 0xffff) + BASE - 1;
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149 | sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
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150 | if (sum1 >= BASE) sum1 -= BASE;
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151 | if (sum1 >= BASE) sum1 -= BASE;
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152 | if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
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153 | if (sum2 >= BASE) sum2 -= BASE;
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154 | return sum1 | (sum2 << 16);
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155 | }
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156 |
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157 | /* ========================================================================= */
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158 | uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2) {
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159 | return adler32_combine_(adler1, adler2, len2);
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160 | }
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161 |
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162 | uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) {
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163 | return adler32_combine_(adler1, adler2, len2);
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164 | }
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