1 | /* Integer base 2 logarithm calculation |
---|---|

2 | * |

3 | * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. |

4 | * Written by David Howells (dhowells@redhat.com) |

5 | * |

6 | * This program is free software; you can redistribute it and/or |

7 | * modify it under the terms of the GNU General Public License |

8 | * as published by the Free Software Foundation; either version |

9 | * 2 of the License, or (at your option) any later version. |

10 | */ |

11 | |

12 | #ifndef _LINUX_LOG2_H |

13 | #define _LINUX_LOG2_H |

14 | |

15 | #include <linux/types.h> |

16 | #include <linux/bitops.h> |

17 | |

18 | /* |

19 | * non-constant log of base 2 calculators |

20 | * - the arch may override these in asm/bitops.h if they can be implemented |

21 | * more efficiently than using fls() and fls64() |

22 | * - the arch is not required to handle n==0 if implementing the fallback |

23 | */ |

24 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |

25 | static inline __attribute__((const)) |

26 | int __ilog2_u32(u32 n) |

27 | { |

28 | return fls(n) - 1; |

29 | } |

30 | #endif |

31 | |

32 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |

33 | static inline __attribute__((const)) |

34 | int __ilog2_u64(u64 n) |

35 | { |

36 | return fls64(n) - 1; |

37 | } |

38 | #endif |

39 | |

40 | /** |

41 | * is_power_of_2() - check if a value is a power of two |

42 | * @n: the value to check |

43 | * |

44 | * Determine whether some value is a power of two, where zero is |

45 | * *not* considered a power of two. |

46 | * Return: true if @n is a power of 2, otherwise false. |

47 | */ |

48 | static inline __attribute__((const)) |

49 | bool is_power_of_2(unsigned long n) |

50 | { |

51 | return (n != 0 && ((n & (n - 1)) == 0)); |

52 | } |

53 | |

54 | /** |

55 | * __roundup_pow_of_two() - round up to nearest power of two |

56 | * @n: value to round up |

57 | */ |

58 | static inline __attribute__((const)) |

59 | unsigned long __roundup_pow_of_two(unsigned long n) |

60 | { |

61 | return 1UL << fls_long(n - 1); |

62 | } |

63 | |

64 | /** |

65 | * __rounddown_pow_of_two() - round down to nearest power of two |

66 | * @n: value to round down |

67 | */ |

68 | static inline __attribute__((const)) |

69 | unsigned long __rounddown_pow_of_two(unsigned long n) |

70 | { |

71 | return 1UL << (fls_long(n) - 1); |

72 | } |

73 | |

74 | /** |

75 | * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value |

76 | * @n: parameter |

77 | * |

78 | * Use this where sparse expects a true constant expression, e.g. for array |

79 | * indices. |

80 | */ |

81 | #define const_ilog2(n) \ |

82 | ( \ |

83 | __builtin_constant_p(n) ? ( \ |

84 | (n) < 2 ? 0 : \ |

85 | (n) & (1ULL << 63) ? 63 : \ |

86 | (n) & (1ULL << 62) ? 62 : \ |

87 | (n) & (1ULL << 61) ? 61 : \ |

88 | (n) & (1ULL << 60) ? 60 : \ |

89 | (n) & (1ULL << 59) ? 59 : \ |

90 | (n) & (1ULL << 58) ? 58 : \ |

91 | (n) & (1ULL << 57) ? 57 : \ |

92 | (n) & (1ULL << 56) ? 56 : \ |

93 | (n) & (1ULL << 55) ? 55 : \ |

94 | (n) & (1ULL << 54) ? 54 : \ |

95 | (n) & (1ULL << 53) ? 53 : \ |

96 | (n) & (1ULL << 52) ? 52 : \ |

97 | (n) & (1ULL << 51) ? 51 : \ |

98 | (n) & (1ULL << 50) ? 50 : \ |

99 | (n) & (1ULL << 49) ? 49 : \ |

100 | (n) & (1ULL << 48) ? 48 : \ |

101 | (n) & (1ULL << 47) ? 47 : \ |

102 | (n) & (1ULL << 46) ? 46 : \ |

103 | (n) & (1ULL << 45) ? 45 : \ |

104 | (n) & (1ULL << 44) ? 44 : \ |

105 | (n) & (1ULL << 43) ? 43 : \ |

106 | (n) & (1ULL << 42) ? 42 : \ |

107 | (n) & (1ULL << 41) ? 41 : \ |

108 | (n) & (1ULL << 40) ? 40 : \ |

109 | (n) & (1ULL << 39) ? 39 : \ |

110 | (n) & (1ULL << 38) ? 38 : \ |

111 | (n) & (1ULL << 37) ? 37 : \ |

112 | (n) & (1ULL << 36) ? 36 : \ |

113 | (n) & (1ULL << 35) ? 35 : \ |

114 | (n) & (1ULL << 34) ? 34 : \ |

115 | (n) & (1ULL << 33) ? 33 : \ |

116 | (n) & (1ULL << 32) ? 32 : \ |

117 | (n) & (1ULL << 31) ? 31 : \ |

118 | (n) & (1ULL << 30) ? 30 : \ |

119 | (n) & (1ULL << 29) ? 29 : \ |

120 | (n) & (1ULL << 28) ? 28 : \ |

121 | (n) & (1ULL << 27) ? 27 : \ |

122 | (n) & (1ULL << 26) ? 26 : \ |

123 | (n) & (1ULL << 25) ? 25 : \ |

124 | (n) & (1ULL << 24) ? 24 : \ |

125 | (n) & (1ULL << 23) ? 23 : \ |

126 | (n) & (1ULL << 22) ? 22 : \ |

127 | (n) & (1ULL << 21) ? 21 : \ |

128 | (n) & (1ULL << 20) ? 20 : \ |

129 | (n) & (1ULL << 19) ? 19 : \ |

130 | (n) & (1ULL << 18) ? 18 : \ |

131 | (n) & (1ULL << 17) ? 17 : \ |

132 | (n) & (1ULL << 16) ? 16 : \ |

133 | (n) & (1ULL << 15) ? 15 : \ |

134 | (n) & (1ULL << 14) ? 14 : \ |

135 | (n) & (1ULL << 13) ? 13 : \ |

136 | (n) & (1ULL << 12) ? 12 : \ |

137 | (n) & (1ULL << 11) ? 11 : \ |

138 | (n) & (1ULL << 10) ? 10 : \ |

139 | (n) & (1ULL << 9) ? 9 : \ |

140 | (n) & (1ULL << 8) ? 8 : \ |

141 | (n) & (1ULL << 7) ? 7 : \ |

142 | (n) & (1ULL << 6) ? 6 : \ |

143 | (n) & (1ULL << 5) ? 5 : \ |

144 | (n) & (1ULL << 4) ? 4 : \ |

145 | (n) & (1ULL << 3) ? 3 : \ |

146 | (n) & (1ULL << 2) ? 2 : \ |

147 | 1) : \ |

148 | -1) |

149 | |

150 | /** |

151 | * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value |

152 | * @n: parameter |

153 | * |

154 | * constant-capable log of base 2 calculation |

155 | * - this can be used to initialise global variables from constant data, hence |

156 | * the massive ternary operator construction |

157 | * |

158 | * selects the appropriately-sized optimised version depending on sizeof(n) |

159 | */ |

160 | #define ilog2(n) \ |

161 | ( \ |

162 | __builtin_constant_p(n) ? \ |

163 | const_ilog2(n) : \ |

164 | (sizeof(n) <= 4) ? \ |

165 | __ilog2_u32(n) : \ |

166 | __ilog2_u64(n) \ |

167 | ) |

168 | |

169 | /** |

170 | * roundup_pow_of_two - round the given value up to nearest power of two |

171 | * @n: parameter |

172 | * |

173 | * round the given value up to the nearest power of two |

174 | * - the result is undefined when n == 0 |

175 | * - this can be used to initialise global variables from constant data |

176 | */ |

177 | #define roundup_pow_of_two(n) \ |

178 | ( \ |

179 | __builtin_constant_p(n) ? ( \ |

180 | (n == 1) ? 1 : \ |

181 | (1UL << (ilog2((n) - 1) + 1)) \ |

182 | ) : \ |

183 | __roundup_pow_of_two(n) \ |

184 | ) |

185 | |

186 | /** |

187 | * rounddown_pow_of_two - round the given value down to nearest power of two |

188 | * @n: parameter |

189 | * |

190 | * round the given value down to the nearest power of two |

191 | * - the result is undefined when n == 0 |

192 | * - this can be used to initialise global variables from constant data |

193 | */ |

194 | #define rounddown_pow_of_two(n) \ |

195 | ( \ |

196 | __builtin_constant_p(n) ? ( \ |

197 | (1UL << ilog2(n))) : \ |

198 | __rounddown_pow_of_two(n) \ |

199 | ) |

200 | |

201 | static inline __attribute_const__ |

202 | int __order_base_2(unsigned long n) |

203 | { |

204 | return n > 1 ? ilog2(n - 1) + 1 : 0; |

205 | } |

206 | |

207 | /** |

208 | * order_base_2 - calculate the (rounded up) base 2 order of the argument |

209 | * @n: parameter |

210 | * |

211 | * The first few values calculated by this routine: |

212 | * ob2(0) = 0 |

213 | * ob2(1) = 0 |

214 | * ob2(2) = 1 |

215 | * ob2(3) = 2 |

216 | * ob2(4) = 2 |

217 | * ob2(5) = 3 |

218 | * ... and so on. |

219 | */ |

220 | #define order_base_2(n) \ |

221 | ( \ |

222 | __builtin_constant_p(n) ? ( \ |

223 | ((n) == 0 || (n) == 1) ? 0 : \ |

224 | ilog2((n) - 1) + 1) : \ |

225 | __order_base_2(n) \ |

226 | ) |

227 | #endif /* _LINUX_LOG2_H */ |

228 |