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132
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1 /**
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2 * This module contains a collection of bit-level operations.
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3 *
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4 * Copyright: Public Domain
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5 * License: Public Domain
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6 * Authors: Sean Kelly
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7 */
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8 module tango.core.BitManip;
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9
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10
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11 version( DDoc )
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12 {
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13 /**
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14 * Scans the bits in v starting with bit 0, looking
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15 * for the first set bit.
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16 * Returns:
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17 * The bit number of the first bit set.
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18 * The return value is undefined if v is zero.
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19 */
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20 int bsf( uint v );
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21
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22
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23 /**
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24 * Scans the bits in v from the most significant bit
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25 * to the least significant bit, looking
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26 * for the first set bit.
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27 * Returns:
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28 * The bit number of the first bit set.
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29 * The return value is undefined if v is zero.
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30 * Example:
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31 * ---
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32 * import std.intrinsic;
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33 *
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34 * int main()
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35 * {
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36 * uint v;
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37 * int x;
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38 *
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39 * v = 0x21;
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40 * x = bsf(v);
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41 * printf("bsf(x%x) = %d\n", v, x);
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42 * x = bsr(v);
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43 * printf("bsr(x%x) = %d\n", v, x);
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44 * return 0;
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45 * }
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46 * ---
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47 * Output:
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48 * bsf(x21) = 0<br>
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49 * bsr(x21) = 5
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50 */
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51 int bsr( uint v );
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52
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53
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54 /**
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55 * Tests the bit.
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56 */
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57 int bt( uint* p, uint bitnum );
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58
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59
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60 /**
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61 * Tests and complements the bit.
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62 */
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63 int btc( uint* p, uint bitnum );
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64
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65
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66 /**
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67 * Tests and resets (sets to 0) the bit.
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68 */
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69 int btr( uint* p, uint bitnum );
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70
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71
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72 /**
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73 * Tests and sets the bit.
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74 * Params:
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75 * p = a non-NULL pointer to an array of uints.
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76 * index = a bit number, starting with bit 0 of p[0],
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77 * and progressing. It addresses bits like the expression:
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78 ---
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79 p[index / (uint.sizeof*8)] & (1 << (index & ((uint.sizeof*8) - 1)))
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80 ---
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81 * Returns:
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82 * A non-zero value if the bit was set, and a zero
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83 * if it was clear.
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84 *
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85 * Example:
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86 * ---
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87 import std.intrinsic;
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88
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89 int main()
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90 {
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91 uint array[2];
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92
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93 array[0] = 2;
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94 array[1] = 0x100;
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95
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96 printf("btc(array, 35) = %d\n", <b>btc</b>(array, 35));
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97 printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);
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98
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99 printf("btc(array, 35) = %d\n", <b>btc</b>(array, 35));
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100 printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);
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101
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102 printf("bts(array, 35) = %d\n", <b>bts</b>(array, 35));
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103 printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);
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104
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105 printf("btr(array, 35) = %d\n", <b>btr</b>(array, 35));
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106 printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);
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107
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108 printf("bt(array, 1) = %d\n", <b>bt</b>(array, 1));
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109 printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);
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110
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111 return 0;
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112 }
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113 * ---
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114 * Output:
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115 <pre>
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116 btc(array, 35) = 0
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117 array = [0]:x2, [1]:x108
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118 btc(array, 35) = -1
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119 array = [0]:x2, [1]:x100
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120 bts(array, 35) = 0
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121 array = [0]:x2, [1]:x108
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122 btr(array, 35) = -1
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123 array = [0]:x2, [1]:x100
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124 bt(array, 1) = -1
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125 array = [0]:x2, [1]:x100
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126 </pre>
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127 */
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128 int bts( uint* p, uint bitnum );
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129
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130
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131 /**
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132 * Swaps bytes in a 4 byte uint end-to-end, i.e. byte 0 becomes
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133 * byte 3, byte 1 becomes byte 2, byte 2 becomes byte 1, byte 3
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134 * becomes byte 0.
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135 */
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136 uint bswap( uint v );
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137
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138
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139 /**
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140 * Reads I/O port at port_address.
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141 */
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142 ubyte inp( uint port_address );
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143
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144
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145 /**
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146 * ditto
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147 */
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148 ushort inpw( uint port_address );
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149
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150
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151 /**
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152 * ditto
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153 */
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154 uint inpl( uint port_address );
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155
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156
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157 /**
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158 * Writes and returns value to I/O port at port_address.
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159 */
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160 ubyte outp( uint port_address, ubyte value );
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161
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162
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163 /**
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164 * ditto
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165 */
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166 ushort outpw( uint port_address, ushort value );
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167
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168
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169 /**
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170 * ditto
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171 */
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172 uint outpl( uint port_address, uint value );
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173 }
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174 else
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175 {
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176 public import std.intrinsic;
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177 }
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178
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179
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180 /**
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181 * Calculates the number of set bits in a 32-bit integer.
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182 */
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183 int popcnt( uint x )
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184 {
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185 // Avoid branches, and the potential for cache misses which
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186 // could be incurred with a table lookup.
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187
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188 // We need to mask alternate bits to prevent the
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189 // sum from overflowing.
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190 // add neighbouring bits. Each bit is 0 or 1.
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191 x = x - ((x>>1) & 0x5555_5555);
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192 // now each two bits of x is a number 00,01 or 10.
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193 // now add neighbouring pairs
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194 x = ((x&0xCCCC_CCCC)>>2) + (x&0x3333_3333);
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195 // now each nibble holds 0000-0100. Adding them won't
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196 // overflow any more, so we don't need to mask any more
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197
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198 // Now add the nibbles, then the bytes, then the words
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199 // We still need to mask to prevent double-counting.
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200 // Note that if we used a rotate instead of a shift, we
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201 // wouldn't need the masks, and could just divide the sum
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202 // by 8 to account for the double-counting.
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203 // On some CPUs, it may be faster to perform a multiply.
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204
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205 x += (x>>4);
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206 x &= 0x0F0F_0F0F;
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207 x += (x>>8);
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208 x &= 0x00FF_00FF;
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209 x += (x>>16);
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210 x &= 0xFFFF;
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211 return x;
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212 }
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213
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214
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215 debug( UnitTest )
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216 {
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217 unittest
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218 {
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219 assert( popcnt( 0 ) == 0 );
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220 assert( popcnt( 7 ) == 3 );
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221 assert( popcnt( 0xAA )== 4 );
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222 assert( popcnt( 0x8421_1248 ) == 8 );
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223 assert( popcnt( 0xFFFF_FFFF ) == 32 );
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224 assert( popcnt( 0xCCCC_CCCC ) == 16 );
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225 assert( popcnt( 0x7777_7777 ) == 24 );
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226 }
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227 }
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228
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229
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230 /**
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231 * Reverses the order of bits in a 32-bit integer.
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232 */
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233 uint bitswap( uint x )
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234 {
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235
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236 version( D_InlineAsm_X86 )
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237 {
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238 asm
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239 {
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240 // Author: Tiago Gasiba.
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241 mov EDX, EAX;
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242 shr EAX, 1;
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243 and EDX, 0x5555_5555;
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244 and EAX, 0x5555_5555;
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245 shl EDX, 1;
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246 or EAX, EDX;
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247 mov EDX, EAX;
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248 shr EAX, 2;
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249 and EDX, 0x3333_3333;
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250 and EAX, 0x3333_3333;
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251 shl EDX, 2;
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252 or EAX, EDX;
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253 mov EDX, EAX;
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254 shr EAX, 4;
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255 and EDX, 0x0f0f_0f0f;
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256 and EAX, 0x0f0f_0f0f;
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257 shl EDX, 4;
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258 or EAX, EDX;
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259 bswap EAX;
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260 }
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261 }
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262 else
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263 {
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264 // swap odd and even bits
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265 x = ((x >> 1) & 0x5555_5555) | ((x & 0x5555_5555) << 1);
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266 // swap consecutive pairs
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267 x = ((x >> 2) & 0x3333_3333) | ((x & 0x3333_3333) << 2);
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268 // swap nibbles
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269 x = ((x >> 4) & 0x0F0F_0F0F) | ((x & 0x0F0F_0F0F) << 4);
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270 // swap bytes
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271 x = ((x >> 8) & 0x00FF_00FF) | ((x & 0x00FF_00FF) << 8);
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272 // swap 2-byte long pairs
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273 x = ( x >> 16 ) | ( x << 16);
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274 return x;
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275
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276 }
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277 }
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278
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279
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280 debug( UnitTest )
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281 {
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282 unittest
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283 {
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284 assert( bitswap( 0x8000_0100 ) == 0x0080_0001 );
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285 }
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286 }
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