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annotate zlib/adler32.c @ 1830:2f3600e204b0

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Update build_release script to support Win64
author Michael Pavone <pavone@retrodev.com>
date Sun, 07 Apr 2019 22:53:23 -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 }