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1 /* adler32.cpp -- 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.cpp,v 1.1.2.1 2008/08/14 15:26:57 e0222316 Exp $ */ |
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7 |
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8 #define ZLIB_INTERNAL |
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9 #include "libzcore.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 |
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58 |
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59 #ifdef __SYMBIAN32__ |
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60 EXPORT_C uLong adler32_r(uLong adler,const Bytef * buf,uInt len) |
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61 #else |
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62 uLong ZEXPORT adler32(adler, buf, len) |
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63 uLong adler; |
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64 const Bytef *buf; |
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65 uInt len; |
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66 #endif /* __SYMBIAN32__ */ |
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67 { |
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68 unsigned long sum2; |
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69 unsigned n; |
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70 |
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71 /* split Adler-32 into component sums */ |
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72 sum2 = (adler >> 16) & 0xffff; |
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73 adler &= 0xffff; |
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74 |
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75 /* in case user likes doing a byte at a time, keep it fast */ |
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76 if (len == 1) { |
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77 adler += buf[0]; |
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78 if (adler >= BASE) |
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79 adler -= BASE; |
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80 sum2 += adler; |
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81 if (sum2 >= BASE) |
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82 sum2 -= BASE; |
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83 return adler | (sum2 << 16); |
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84 } |
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85 |
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86 /* initial Adler-32 value (deferred check for len == 1 speed) */ |
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87 if (buf == Z_NULL) |
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88 return 1L; |
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89 |
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90 /* in case short lengths are provided, keep it somewhat fast */ |
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91 if (len < 16) { |
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92 while (len--) { |
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93 adler += *buf++; |
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94 sum2 += adler; |
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95 } |
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96 if (adler >= BASE) |
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97 adler -= BASE; |
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98 MOD4(sum2); /* only added so many BASE's */ |
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99 return adler | (sum2 << 16); |
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100 } |
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101 |
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102 /* do length NMAX blocks -- requires just one modulo operation */ |
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103 while (len >= NMAX) { |
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104 len -= NMAX; |
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105 n = NMAX / 16; /* NMAX is divisible by 16 */ |
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106 do { |
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107 DO16(buf); /* 16 sums unrolled */ |
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108 buf += 16; |
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109 } while (--n); |
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110 MOD(adler); |
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111 MOD(sum2); |
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112 } |
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113 |
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114 /* do remaining bytes (less than NMAX, still just one modulo) */ |
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115 if (len) { /* avoid modulos if none remaining */ |
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116 while (len >= 16) { |
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117 len -= 16; |
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118 DO16(buf); |
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119 buf += 16; |
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120 } |
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121 while (len--) { |
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122 adler += *buf++; |
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123 sum2 += adler; |
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124 } |
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125 MOD(adler); |
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126 MOD(sum2); |
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127 } |
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128 |
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129 /* return recombined sums */ |
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130 return adler | (sum2 << 16); |
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131 } |
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132 |
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133 /* ========================================================================= */ |
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134 |
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135 #ifdef __SYMBIAN32__ |
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136 EXPORT_C uLong adler32_combine_r(uLong adler1, uLong adler2, z_off_t len2) |
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137 #else |
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138 uLong ZEXPORT adler32_combine(adler1, adler2, len2) |
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139 uLong adler1; |
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140 uLong adler2; |
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141 z_off_t len2; |
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142 #endif /* __SYMBIAN32__ */ |
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143 { |
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144 unsigned long sum1; |
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145 unsigned long sum2; |
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146 unsigned rem; |
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147 |
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148 /* the derivation of this formula is left as an exercise for the reader */ |
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149 rem = (unsigned)(len2 % BASE); |
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150 sum1 = adler1 & 0xffff; |
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151 sum2 = rem * sum1; |
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152 MOD(sum2); |
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153 sum1 += (adler2 & 0xffff) + BASE - 1; |
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154 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; |
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155 if (sum1 > BASE) sum1 -= BASE; |
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156 if (sum1 > BASE) sum1 -= BASE; |
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157 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1); |
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158 if (sum2 > BASE) sum2 -= BASE; |
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159 return sum1 | (sum2 << 16); |
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160 } |