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5
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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * bit_operations.h - Various bit level operations, such as bit reversal
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2006 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * $Id: bit_operations.h,v 1.11 2006/11/28 15:37:03 steveu Exp $
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26 */
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27
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28 /*! \file */
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29
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30 #if !defined(_BIT_OPERATIONS_H_)
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31 #define _BIT_OPERATIONS_H_
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32
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33 #ifdef __cplusplus
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34 extern "C" {
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35 #endif
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36
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37 #if defined(__i386__) || defined(__x86_64__)
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38 /*! \brief Find the bit position of the highest set bit in a word
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39 \param bits The word to be searched
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40 \return The bit number of the highest set bit, or -1 if the word is zero. */
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41 static __inline__ int top_bit(unsigned int bits)
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42 {
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43 int res;
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44
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45 __asm__ (" xorl %[res],%[res];\n"
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46 " decl %[res];\n"
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47 " bsrl %[bits],%[res]\n"
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48 : [res] "=&r" (res)
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49 : [bits] "rm" (bits));
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50 return res;
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51 }
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52 /*- End of function --------------------------------------------------------*/
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53
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54 /*! \brief Find the bit position of the lowest set bit in a word
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55 \param bits The word to be searched
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56 \return The bit number of the lowest set bit, or -1 if the word is zero. */
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57 static __inline__ int bottom_bit(unsigned int bits)
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58 {
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59 int res;
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60
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61 __asm__ (" xorl %[res],%[res];\n"
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62 " decl %[res];\n"
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63 " bsfl %[bits],%[res]\n"
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64 : [res] "=&r" (res)
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65 : [bits] "rm" (bits));
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66 return res;
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67 }
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68 /*- End of function --------------------------------------------------------*/
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69 #else
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70 static __inline__ int top_bit(unsigned int bits)
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71 {
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72 int i;
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73
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74 if (bits == 0)
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75 return -1;
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76 i = 0;
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77 if (bits & 0xFFFF0000)
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78 {
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79 bits &= 0xFFFF0000;
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80 i += 16;
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81 }
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82 if (bits & 0xFF00FF00)
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83 {
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84 bits &= 0xFF00FF00;
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85 i += 8;
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86 }
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87 if (bits & 0xF0F0F0F0)
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88 {
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89 bits &= 0xF0F0F0F0;
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90 i += 4;
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91 }
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92 if (bits & 0xCCCCCCCC)
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93 {
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94 bits &= 0xCCCCCCCC;
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95 i += 2;
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96 }
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97 if (bits & 0xAAAAAAAA)
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98 {
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99 bits &= 0xAAAAAAAA;
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100 i += 1;
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101 }
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102 return i;
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103 }
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104 /*- End of function --------------------------------------------------------*/
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105
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106 static __inline__ int bottom_bit(unsigned int bits)
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107 {
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108 int i;
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109
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110 if (bits == 0)
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111 return -1;
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112 i = 32;
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113 if (bits & 0x0000FFFF)
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114 {
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115 bits &= 0x0000FFFF;
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116 i -= 16;
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117 }
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118 if (bits & 0x00FF00FF)
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119 {
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120 bits &= 0x00FF00FF;
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121 i -= 8;
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122 }
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123 if (bits & 0x0F0F0F0F)
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124 {
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125 bits &= 0x0F0F0F0F;
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126 i -= 4;
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127 }
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128 if (bits & 0x33333333)
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129 {
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130 bits &= 0x33333333;
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131 i -= 2;
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132 }
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133 if (bits & 0x55555555)
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134 {
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135 bits &= 0x55555555;
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136 i -= 1;
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137 }
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138 return i;
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139 }
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140 /*- End of function --------------------------------------------------------*/
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141 #endif
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142
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143 /*! \brief Bit reverse a byte.
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144 \param data The byte to be reversed.
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145 \return The bit reversed version of data. */
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146 static __inline__ uint8_t bit_reverse8(uint8_t x)
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147 {
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148 #if defined(__i386__) || defined(__x86_64__)
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149 /* If multiply is fast */
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150 return ((x*0x0802U & 0x22110U) | (x*0x8020U & 0x88440U))*0x10101U >> 16;
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151 #else
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152 /* If multiply is slow, but we have a barrel shifter */
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153 x = (x >> 4) | (x << 4);
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154 x = ((x & 0xCC) >> 2) | ((x & 0x33) << 2);
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155 return ((x & 0xAA) >> 1) | ((x & 0x55) << 1);
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156 #endif
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157 }
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158 /*- End of function --------------------------------------------------------*/
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159
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160 /*! \brief Bit reverse a 16 bit word.
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161 \param data The word to be reversed.
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162 \return The bit reversed version of data. */
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163 uint16_t bit_reverse16(uint16_t data);
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164
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165 /*! \brief Bit reverse a 32 bit word.
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166 \param data The word to be reversed.
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167 \return The bit reversed version of data. */
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168 uint32_t bit_reverse32(uint32_t data);
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169
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170 /*! \brief Bit reverse each of the four bytes in a 32 bit word.
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171 \param data The word to be reversed.
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172 \return The bit reversed version of data. */
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173 uint32_t bit_reverse_4bytes(uint32_t data);
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174
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175 /*! \brief Find the number of set bits in a 32 bit word.
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176 \param x The word to be searched.
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177 \return The number of set bits. */
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178 int one_bits32(uint32_t x);
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179
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180 /*! \brief Create a mask as wide as the number in a 32 bit word.
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181 \param x The word to be searched.
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182 \return The mask. */
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183 uint32_t make_mask32(uint32_t x);
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184
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185 /*! \brief Create a mask as wide as the number in a 16 bit word.
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186 \param x The word to be searched.
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187 \return The mask. */
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188 uint16_t make_mask16(uint16_t x);
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189
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190 /*! \brief Find the least significant one in a word, and return a word
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191 with just that bit set.
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192 \param x The word to be searched.
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193 \return The word with the single set bit. */
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194 static __inline__ uint32_t least_significant_one32(uint32_t x)
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195 {
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196 return (x & (-(int32_t) x));
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197 }
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198 /*- End of function --------------------------------------------------------*/
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199
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200 /*! \brief Find the most significant one in a word, and return a word
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201 with just that bit set.
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202 \param x The word to be searched.
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203 \return The word with the single set bit. */
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204 static __inline__ uint32_t most_significant_one32(uint32_t x)
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205 {
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206 #if defined(__i386__) || defined(__x86_64__)
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207 return 1 << top_bit(x);
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208 #else
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209 x = make_mask32(x);
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210 return (x ^ (x >> 1));
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211 #endif
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212 }
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213 /*- End of function --------------------------------------------------------*/
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214
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215 /*! \brief Find the parity of a byte.
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216 \param x The byte to be checked.
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217 \return 1 for odd, or 0 for even. */
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218 static __inline__ int parity8(uint8_t x)
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219 {
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220 x = (x ^ (x >> 4)) & 0x0F;
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221 return (0x6996 >> x) & 1;
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222 }
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223 /*- End of function --------------------------------------------------------*/
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224
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225 /*! \brief Find the parity of a 16 bit word.
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226 \param x The word to be checked.
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227 \return 1 for odd, or 0 for even. */
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228 static __inline__ int parity16(uint16_t x)
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229 {
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230 x ^= (x >> 8);
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231 x = (x ^ (x >> 4)) & 0x0F;
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232 return (0x6996 >> x) & 1;
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233 }
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234 /*- End of function --------------------------------------------------------*/
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235
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236 /*! \brief Find the parity of a 32 bit word.
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237 \param x The word to be checked.
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238 \return 1 for odd, or 0 for even. */
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239 static __inline__ int parity32(uint32_t x)
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240 {
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241 x ^= (x >> 16);
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242 x ^= (x >> 8);
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243 x = (x ^ (x >> 4)) & 0x0F;
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244 return (0x6996 >> x) & 1;
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245 }
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246 /*- End of function --------------------------------------------------------*/
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247
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248 #ifdef __cplusplus
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249 }
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250 #endif
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251
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252 #endif
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253 /*- End of file ------------------------------------------------------------*/
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