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1 /* Integer base 2 logarithm calculation |
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2 * |
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3 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. |
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4 * Written by David Howells (dhowells@redhat.com) |
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5 * |
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6 * This program is free software; you can redistribute it and/or |
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7 * modify it under the terms of the GNU General Public License |
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8 * as published by the Free Software Foundation; either version |
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9 * 2 of the License, or (at your option) any later version. |
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10 */ |
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11 |
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12 #ifndef _LINUX_LOG2_H |
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13 #define _LINUX_LOG2_H |
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14 |
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15 #include <linux/types.h> |
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16 #include <linux/bitops.h> |
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17 |
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18 /* |
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19 * deal with unrepresentable constant logarithms |
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20 */ |
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21 extern __attribute__((const, noreturn)) |
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22 int ____ilog2_NaN(void); |
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23 |
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24 /* |
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25 * non-constant log of base 2 calculators |
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26 * - the arch may override these in asm/bitops.h if they can be implemented |
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27 * more efficiently than using fls() and fls64() |
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28 * - the arch is not required to handle n==0 if implementing the fallback |
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29 */ |
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30 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |
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31 static inline __attribute__((const)) |
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32 int __ilog2_u32(u32 n) |
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33 { |
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34 return fls(n) - 1; |
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35 } |
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36 #endif |
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37 |
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38 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |
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39 static inline __attribute__((const)) |
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40 int __ilog2_u64(u64 n) |
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41 { |
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42 return fls64(n) - 1; |
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43 } |
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44 #endif |
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45 |
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46 /* |
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47 * Determine whether some value is a power of two, where zero is |
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48 * *not* considered a power of two. |
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49 */ |
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50 |
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51 static inline __attribute__((const)) |
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52 bool is_power_of_2(unsigned long n) |
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53 { |
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54 return (n != 0 && ((n & (n - 1)) == 0)); |
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55 } |
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56 |
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57 /* |
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58 * round up to nearest power of two |
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59 */ |
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60 static inline __attribute__((const)) |
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61 unsigned long __roundup_pow_of_two(unsigned long n) |
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62 { |
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63 return 1UL << fls_long(n - 1); |
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64 } |
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65 |
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66 /* |
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67 * round down to nearest power of two |
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68 */ |
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69 static inline __attribute__((const)) |
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70 unsigned long __rounddown_pow_of_two(unsigned long n) |
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71 { |
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72 return 1UL << (fls_long(n) - 1); |
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73 } |
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74 |
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75 /** |
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76 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value |
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77 * @n - parameter |
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78 * |
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79 * constant-capable log of base 2 calculation |
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80 * - this can be used to initialise global variables from constant data, hence |
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81 * the massive ternary operator construction |
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82 * |
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83 * selects the appropriately-sized optimised version depending on sizeof(n) |
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84 */ |
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85 #define ilog2(n) \ |
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86 ( \ |
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87 __builtin_constant_p(n) ? ( \ |
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88 (n) < 1 ? ____ilog2_NaN() : \ |
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89 (n) & (1ULL << 63) ? 63 : \ |
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90 (n) & (1ULL << 62) ? 62 : \ |
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91 (n) & (1ULL << 61) ? 61 : \ |
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92 (n) & (1ULL << 60) ? 60 : \ |
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93 (n) & (1ULL << 59) ? 59 : \ |
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94 (n) & (1ULL << 58) ? 58 : \ |
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95 (n) & (1ULL << 57) ? 57 : \ |
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96 (n) & (1ULL << 56) ? 56 : \ |
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97 (n) & (1ULL << 55) ? 55 : \ |
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98 (n) & (1ULL << 54) ? 54 : \ |
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99 (n) & (1ULL << 53) ? 53 : \ |
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100 (n) & (1ULL << 52) ? 52 : \ |
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101 (n) & (1ULL << 51) ? 51 : \ |
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102 (n) & (1ULL << 50) ? 50 : \ |
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103 (n) & (1ULL << 49) ? 49 : \ |
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104 (n) & (1ULL << 48) ? 48 : \ |
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105 (n) & (1ULL << 47) ? 47 : \ |
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106 (n) & (1ULL << 46) ? 46 : \ |
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107 (n) & (1ULL << 45) ? 45 : \ |
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108 (n) & (1ULL << 44) ? 44 : \ |
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109 (n) & (1ULL << 43) ? 43 : \ |
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110 (n) & (1ULL << 42) ? 42 : \ |
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111 (n) & (1ULL << 41) ? 41 : \ |
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112 (n) & (1ULL << 40) ? 40 : \ |
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113 (n) & (1ULL << 39) ? 39 : \ |
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114 (n) & (1ULL << 38) ? 38 : \ |
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115 (n) & (1ULL << 37) ? 37 : \ |
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116 (n) & (1ULL << 36) ? 36 : \ |
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117 (n) & (1ULL << 35) ? 35 : \ |
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118 (n) & (1ULL << 34) ? 34 : \ |
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119 (n) & (1ULL << 33) ? 33 : \ |
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120 (n) & (1ULL << 32) ? 32 : \ |
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121 (n) & (1ULL << 31) ? 31 : \ |
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122 (n) & (1ULL << 30) ? 30 : \ |
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123 (n) & (1ULL << 29) ? 29 : \ |
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124 (n) & (1ULL << 28) ? 28 : \ |
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125 (n) & (1ULL << 27) ? 27 : \ |
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126 (n) & (1ULL << 26) ? 26 : \ |
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127 (n) & (1ULL << 25) ? 25 : \ |
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128 (n) & (1ULL << 24) ? 24 : \ |
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129 (n) & (1ULL << 23) ? 23 : \ |
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130 (n) & (1ULL << 22) ? 22 : \ |
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131 (n) & (1ULL << 21) ? 21 : \ |
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132 (n) & (1ULL << 20) ? 20 : \ |
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133 (n) & (1ULL << 19) ? 19 : \ |
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134 (n) & (1ULL << 18) ? 18 : \ |
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135 (n) & (1ULL << 17) ? 17 : \ |
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136 (n) & (1ULL << 16) ? 16 : \ |
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137 (n) & (1ULL << 15) ? 15 : \ |
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138 (n) & (1ULL << 14) ? 14 : \ |
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139 (n) & (1ULL << 13) ? 13 : \ |
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140 (n) & (1ULL << 12) ? 12 : \ |
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141 (n) & (1ULL << 11) ? 11 : \ |
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142 (n) & (1ULL << 10) ? 10 : \ |
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143 (n) & (1ULL << 9) ? 9 : \ |
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144 (n) & (1ULL << 8) ? 8 : \ |
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145 (n) & (1ULL << 7) ? 7 : \ |
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146 (n) & (1ULL << 6) ? 6 : \ |
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147 (n) & (1ULL << 5) ? 5 : \ |
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148 (n) & (1ULL << 4) ? 4 : \ |
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149 (n) & (1ULL << 3) ? 3 : \ |
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150 (n) & (1ULL << 2) ? 2 : \ |
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151 (n) & (1ULL << 1) ? 1 : \ |
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152 (n) & (1ULL << 0) ? 0 : \ |
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153 ____ilog2_NaN() \ |
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154 ) : \ |
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155 (sizeof(n) <= 4) ? \ |
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156 __ilog2_u32(n) : \ |
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157 __ilog2_u64(n) \ |
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158 ) |
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159 |
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160 /** |
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161 * roundup_pow_of_two - round the given value up to nearest power of two |
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162 * @n - parameter |
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163 * |
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164 * round the given value up to the nearest power of two |
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165 * - the result is undefined when n == 0 |
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166 * - this can be used to initialise global variables from constant data |
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167 */ |
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168 #define roundup_pow_of_two(n) \ |
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169 ( \ |
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170 __builtin_constant_p(n) ? ( \ |
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171 (n == 1) ? 1 : \ |
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172 (1UL << (ilog2((n) - 1) + 1)) \ |
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173 ) : \ |
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174 __roundup_pow_of_two(n) \ |
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175 ) |
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176 |
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177 /** |
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178 * rounddown_pow_of_two - round the given value down to nearest power of two |
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179 * @n - parameter |
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180 * |
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181 * round the given value down to the nearest power of two |
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182 * - the result is undefined when n == 0 |
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183 * - this can be used to initialise global variables from constant data |
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184 */ |
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185 #define rounddown_pow_of_two(n) \ |
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186 ( \ |
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187 __builtin_constant_p(n) ? ( \ |
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188 (n == 1) ? 0 : \ |
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189 (1UL << ilog2(n))) : \ |
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190 __rounddown_pow_of_two(n) \ |
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191 ) |
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192 |
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193 /** |
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194 * order_base_2 - calculate the (rounded up) base 2 order of the argument |
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195 * @n: parameter |
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196 * |
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197 * The first few values calculated by this routine: |
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198 * ob2(0) = 0 |
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199 * ob2(1) = 0 |
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200 * ob2(2) = 1 |
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201 * ob2(3) = 2 |
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202 * ob2(4) = 2 |
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203 * ob2(5) = 3 |
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204 * ... and so on. |
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205 */ |
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206 |
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207 #define order_base_2(n) ilog2(roundup_pow_of_two(n)) |
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208 |
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209 #endif /* _LINUX_LOG2_H */ |