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3031 | serge | 1 | /* Integer base 2 logarithm calculation |
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 | |||
12 | #ifndef _LINUX_LOG2_H |
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13 | #define _LINUX_LOG2_H |
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14 | |||
15 | #include |
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16 | #include |
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17 | |||
18 | /* |
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19 | * non-constant log of base 2 calculators |
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20 | * - the arch may override these in asm/bitops.h if they can be implemented |
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21 | * more efficiently than using fls() and fls64() |
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22 | * - the arch is not required to handle n==0 if implementing the fallback |
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23 | */ |
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24 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |
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25 | static inline __attribute__((const)) |
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26 | int __ilog2_u32(u32 n) |
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27 | { |
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28 | return fls(n) - 1; |
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29 | } |
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30 | #endif |
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31 | |||
32 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |
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33 | static inline __attribute__((const)) |
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34 | int __ilog2_u64(u64 n) |
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35 | { |
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36 | return fls64(n) - 1; |
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37 | } |
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38 | #endif |
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39 | |||
40 | /* |
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41 | * Determine whether some value is a power of two, where zero is |
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42 | * *not* considered a power of two. |
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43 | */ |
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44 | |||
45 | static inline __attribute__((const)) |
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46 | bool is_power_of_2(unsigned long n) |
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47 | { |
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48 | return (n != 0 && ((n & (n - 1)) == 0)); |
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49 | } |
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50 | |||
51 | /* |
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52 | * round up to nearest power of two |
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53 | */ |
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54 | static inline __attribute__((const)) |
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55 | unsigned long __roundup_pow_of_two(unsigned long n) |
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56 | { |
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57 | return 1UL << fls_long(n - 1); |
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58 | } |
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59 | |||
60 | /* |
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61 | * round down to nearest power of two |
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62 | */ |
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63 | static inline __attribute__((const)) |
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64 | unsigned long __rounddown_pow_of_two(unsigned long n) |
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65 | { |
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66 | return 1UL << (fls_long(n) - 1); |
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67 | } |
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68 | |||
69 | /** |
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70 | * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value |
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71 | * @n - parameter |
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72 | * |
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73 | * constant-capable log of base 2 calculation |
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74 | * - this can be used to initialise global variables from constant data, hence |
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75 | * the massive ternary operator construction |
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76 | * |
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77 | * selects the appropriately-sized optimised version depending on sizeof(n) |
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78 | */ |
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79 | #define ilog2(n) \ |
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80 | ( \ |
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81 | __builtin_constant_p(n) ? ( \ |
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6934 | serge | 82 | (n) < 2 ? 0 : \ |
3031 | serge | 83 | (n) & (1ULL << 63) ? 63 : \ |
84 | (n) & (1ULL << 62) ? 62 : \ |
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85 | (n) & (1ULL << 61) ? 61 : \ |
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86 | (n) & (1ULL << 60) ? 60 : \ |
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87 | (n) & (1ULL << 59) ? 59 : \ |
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88 | (n) & (1ULL << 58) ? 58 : \ |
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89 | (n) & (1ULL << 57) ? 57 : \ |
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90 | (n) & (1ULL << 56) ? 56 : \ |
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91 | (n) & (1ULL << 55) ? 55 : \ |
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92 | (n) & (1ULL << 54) ? 54 : \ |
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93 | (n) & (1ULL << 53) ? 53 : \ |
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94 | (n) & (1ULL << 52) ? 52 : \ |
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95 | (n) & (1ULL << 51) ? 51 : \ |
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96 | (n) & (1ULL << 50) ? 50 : \ |
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97 | (n) & (1ULL << 49) ? 49 : \ |
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98 | (n) & (1ULL << 48) ? 48 : \ |
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99 | (n) & (1ULL << 47) ? 47 : \ |
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100 | (n) & (1ULL << 46) ? 46 : \ |
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101 | (n) & (1ULL << 45) ? 45 : \ |
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102 | (n) & (1ULL << 44) ? 44 : \ |
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103 | (n) & (1ULL << 43) ? 43 : \ |
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104 | (n) & (1ULL << 42) ? 42 : \ |
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105 | (n) & (1ULL << 41) ? 41 : \ |
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106 | (n) & (1ULL << 40) ? 40 : \ |
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107 | (n) & (1ULL << 39) ? 39 : \ |
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108 | (n) & (1ULL << 38) ? 38 : \ |
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109 | (n) & (1ULL << 37) ? 37 : \ |
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110 | (n) & (1ULL << 36) ? 36 : \ |
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111 | (n) & (1ULL << 35) ? 35 : \ |
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112 | (n) & (1ULL << 34) ? 34 : \ |
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113 | (n) & (1ULL << 33) ? 33 : \ |
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114 | (n) & (1ULL << 32) ? 32 : \ |
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115 | (n) & (1ULL << 31) ? 31 : \ |
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116 | (n) & (1ULL << 30) ? 30 : \ |
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117 | (n) & (1ULL << 29) ? 29 : \ |
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118 | (n) & (1ULL << 28) ? 28 : \ |
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119 | (n) & (1ULL << 27) ? 27 : \ |
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120 | (n) & (1ULL << 26) ? 26 : \ |
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121 | (n) & (1ULL << 25) ? 25 : \ |
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122 | (n) & (1ULL << 24) ? 24 : \ |
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123 | (n) & (1ULL << 23) ? 23 : \ |
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124 | (n) & (1ULL << 22) ? 22 : \ |
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125 | (n) & (1ULL << 21) ? 21 : \ |
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126 | (n) & (1ULL << 20) ? 20 : \ |
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127 | (n) & (1ULL << 19) ? 19 : \ |
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128 | (n) & (1ULL << 18) ? 18 : \ |
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129 | (n) & (1ULL << 17) ? 17 : \ |
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130 | (n) & (1ULL << 16) ? 16 : \ |
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131 | (n) & (1ULL << 15) ? 15 : \ |
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132 | (n) & (1ULL << 14) ? 14 : \ |
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133 | (n) & (1ULL << 13) ? 13 : \ |
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134 | (n) & (1ULL << 12) ? 12 : \ |
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135 | (n) & (1ULL << 11) ? 11 : \ |
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136 | (n) & (1ULL << 10) ? 10 : \ |
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137 | (n) & (1ULL << 9) ? 9 : \ |
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138 | (n) & (1ULL << 8) ? 8 : \ |
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139 | (n) & (1ULL << 7) ? 7 : \ |
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140 | (n) & (1ULL << 6) ? 6 : \ |
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141 | (n) & (1ULL << 5) ? 5 : \ |
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142 | (n) & (1ULL << 4) ? 4 : \ |
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143 | (n) & (1ULL << 3) ? 3 : \ |
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144 | (n) & (1ULL << 2) ? 2 : \ |
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6934 | serge | 145 | 1 ) : \ |
3031 | serge | 146 | (sizeof(n) <= 4) ? \ |
147 | __ilog2_u32(n) : \ |
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148 | __ilog2_u64(n) \ |
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149 | ) |
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150 | |||
151 | /** |
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152 | * roundup_pow_of_two - round the given value up to nearest power of two |
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153 | * @n - parameter |
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154 | * |
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155 | * round the given value up to the nearest power of two |
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156 | * - the result is undefined when n == 0 |
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157 | * - this can be used to initialise global variables from constant data |
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158 | */ |
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159 | #define roundup_pow_of_two(n) \ |
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160 | ( \ |
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161 | __builtin_constant_p(n) ? ( \ |
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162 | (n == 1) ? 1 : \ |
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163 | (1UL << (ilog2((n) - 1) + 1)) \ |
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164 | ) : \ |
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165 | __roundup_pow_of_two(n) \ |
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166 | ) |
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167 | |||
168 | /** |
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169 | * rounddown_pow_of_two - round the given value down to nearest power of two |
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170 | * @n - parameter |
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171 | * |
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172 | * round the given value down to the nearest power of two |
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173 | * - the result is undefined when n == 0 |
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174 | * - this can be used to initialise global variables from constant data |
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175 | */ |
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176 | #define rounddown_pow_of_two(n) \ |
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177 | ( \ |
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178 | __builtin_constant_p(n) ? ( \ |
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179 | (1UL << ilog2(n))) : \ |
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180 | __rounddown_pow_of_two(n) \ |
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181 | ) |
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182 | |||
183 | /** |
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184 | * order_base_2 - calculate the (rounded up) base 2 order of the argument |
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185 | * @n: parameter |
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186 | * |
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187 | * The first few values calculated by this routine: |
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188 | * ob2(0) = 0 |
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189 | * ob2(1) = 0 |
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190 | * ob2(2) = 1 |
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191 | * ob2(3) = 2 |
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192 | * ob2(4) = 2 |
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193 | * ob2(5) = 3 |
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194 | * ... and so on. |
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195 | */ |
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196 | |||
6934 | serge | 197 | static inline __attribute_const__ |
198 | int __order_base_2(unsigned long n) |
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199 | { |
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200 | return n > 1 ? ilog2(n - 1) + 1 : 0; |
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201 | } |
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3031 | serge | 202 | |
6934 | serge | 203 | #define order_base_2(n) \ |
204 | ( \ |
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205 | __builtin_constant_p(n) ? ( \ |
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206 | ((n) == 0 || (n) == 1) ? 0 : \ |
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207 | ilog2((n) - 1) + 1) : \ |
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208 | __order_base_2(n) \ |
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209 | ) |
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3031 | serge | 210 | #endif /* _LINUX_LOG2_H */><>><>=>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>><>>><>><> |