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annotate zlib/adler32.c @ 1971:80920c21bb52

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Add an event log soft flush and call it twice per frame in between hard flushes to netplay latency when there are insufficient hardware updates to flush packets in the middle of a frame
author Michael Pavone <pavone@retrodev.com>
date Fri, 08 May 2020 11:40:30 -0700
parents 00d788dac91a
children
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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 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
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11
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12 #define BASE 65521U /* largest prime smaller than 65536 */
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13 #define NMAX 5552
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14 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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15
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16 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
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17 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
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18 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
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19 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
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20 #define DO16(buf) DO8(buf,0); DO8(buf,8);
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21
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22 /* use NO_DIVIDE if your processor does not do division in hardware --
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23 try it both ways to see which is faster */
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24 #ifdef NO_DIVIDE
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25 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
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26 (thank you to John Reiser for pointing this out) */
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27 # define CHOP(a) \
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28 do { \
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29 unsigned long tmp = a >> 16; \
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30 a &= 0xffffUL; \
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31 a += (tmp << 4) - tmp; \
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32 } while (0)
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33 # define MOD28(a) \
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34 do { \
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35 CHOP(a); \
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36 if (a >= BASE) a -= BASE; \
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37 } while (0)
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38 # define MOD(a) \
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39 do { \
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40 CHOP(a); \
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41 MOD28(a); \
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42 } while (0)
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43 # define MOD63(a) \
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44 do { /* this assumes a is not negative */ \
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45 z_off64_t tmp = a >> 32; \
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46 a &= 0xffffffffL; \
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47 a += (tmp << 8) - (tmp << 5) + tmp; \
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48 tmp = a >> 16; \
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49 a &= 0xffffL; \
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50 a += (tmp << 4) - tmp; \
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51 tmp = a >> 16; \
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52 a &= 0xffffL; \
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53 a += (tmp << 4) - tmp; \
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54 if (a >= BASE) a -= BASE; \
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55 } while (0)
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56 #else
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57 # define MOD(a) a %= BASE
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58 # define MOD28(a) a %= BASE
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59 # define MOD63(a) a %= BASE
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60 #endif
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61
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62 /* ========================================================================= */
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63 uLong ZEXPORT adler32_z(adler, buf, len)
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64 uLong adler;
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65 const Bytef *buf;
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66 z_size_t len;
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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 MOD28(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 uLong ZEXPORT adler32(adler, buf, len)
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135 uLong adler;
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136 const Bytef *buf;
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137 uInt len;
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138 {
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139 return adler32_z(adler, buf, len);
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140 }
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141
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142 /* ========================================================================= */
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143 local uLong adler32_combine_(adler1, adler2, len2)
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144 uLong adler1;
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145 uLong adler2;
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146 z_off64_t len2;
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147 {
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148 unsigned long sum1;
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149 unsigned long sum2;
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150 unsigned rem;
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151
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152 /* for negative len, return invalid adler32 as a clue for debugging */
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153 if (len2 < 0)
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154 return 0xffffffffUL;
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155
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156 /* the derivation of this formula is left as an exercise for the reader */
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157 MOD63(len2); /* assumes len2 >= 0 */
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158 rem = (unsigned)len2;
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159 sum1 = adler1 & 0xffff;
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160 sum2 = rem * sum1;
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161 MOD(sum2);
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162 sum1 += (adler2 & 0xffff) + BASE - 1;
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163 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
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164 if (sum1 >= BASE) sum1 -= BASE;
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165 if (sum1 >= BASE) sum1 -= BASE;
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166 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
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167 if (sum2 >= BASE) sum2 -= BASE;
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168 return sum1 | (sum2 << 16);
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169 }
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170
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171 /* ========================================================================= */
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172 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
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173 uLong adler1;
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174 uLong adler2;
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175 z_off_t len2;
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176 {
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177 return adler32_combine_(adler1, adler2, len2);
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178 }
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179
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180 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
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181 uLong adler1;
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182 uLong adler2;
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183 z_off64_t len2;
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184 {
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185 return adler32_combine_(adler1, adler2, len2);
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186 }