1 | /* SPDX-License-Identifier: GPL-2.0-or-later */ |
---|---|

2 | /* Integer base 2 logarithm calculation |

3 | * |

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

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

6 | */ |

7 | |

8 | #ifndef _LINUX_LOG2_H |

9 | #define _LINUX_LOG2_H |

10 | |

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

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

13 | |

14 | /* |

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

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

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

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

19 | */ |

20 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |

21 | static __always_inline __attribute__((const)) |

22 | int __ilog2_u32(u32 n) |

23 | { |

24 | return fls(x: n) - 1; |

25 | } |

26 | #endif |

27 | |

28 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |

29 | static __always_inline __attribute__((const)) |

30 | int __ilog2_u64(u64 n) |

31 | { |

32 | return fls64(x: n) - 1; |

33 | } |

34 | #endif |

35 | |

36 | /** |

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

38 | * @n: the value to check |

39 | * |

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

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

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

43 | */ |

44 | static inline __attribute__((const)) |

45 | bool is_power_of_2(unsigned long n) |

46 | { |

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

48 | } |

49 | |

50 | /** |

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

52 | * @n: value to round up |

53 | */ |

54 | static inline __attribute__((const)) |

55 | unsigned long __roundup_pow_of_two(unsigned long n) |

56 | { |

57 | return 1UL << fls_long(l: n - 1); |

58 | } |

59 | |

60 | /** |

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

62 | * @n: value to round down |

63 | */ |

64 | static inline __attribute__((const)) |

65 | unsigned long __rounddown_pow_of_two(unsigned long n) |

66 | { |

67 | return 1UL << (fls_long(l: n) - 1); |

68 | } |

69 | |

70 | /** |

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

72 | * @n: parameter |

73 | * |

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

75 | * indices. |

76 | */ |

77 | #define const_ilog2(n) \ |

78 | ( \ |

79 | __builtin_constant_p(n) ? ( \ |

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

143 | 1) : \ |

144 | -1) |

145 | |

146 | /** |

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

148 | * @n: parameter |

149 | * |

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

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

152 | * the massive ternary operator construction |

153 | * |

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

155 | */ |

156 | #define ilog2(n) \ |

157 | ( \ |

158 | __builtin_constant_p(n) ? \ |

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

160 | 63 - __builtin_clzll(n)) : \ |

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

162 | __ilog2_u32(n) : \ |

163 | __ilog2_u64(n) \ |

164 | ) |

165 | |

166 | /** |

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

168 | * @n: parameter |

169 | * |

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

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

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

173 | */ |

174 | #define roundup_pow_of_two(n) \ |

175 | ( \ |

176 | __builtin_constant_p(n) ? ( \ |

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

178 | (1UL << (ilog2((n) - 1) + 1)) \ |

179 | ) : \ |

180 | __roundup_pow_of_two(n) \ |

181 | ) |

182 | |

183 | /** |

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

185 | * @n: parameter |

186 | * |

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

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

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

190 | */ |

191 | #define rounddown_pow_of_two(n) \ |

192 | ( \ |

193 | __builtin_constant_p(n) ? ( \ |

194 | (1UL << ilog2(n))) : \ |

195 | __rounddown_pow_of_two(n) \ |

196 | ) |

197 | |

198 | static inline __attribute_const__ |

199 | int __order_base_2(unsigned long n) |

200 | { |

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

202 | } |

203 | |

204 | /** |

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

206 | * @n: parameter |

207 | * |

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

209 | * ob2(0) = 0 |

210 | * ob2(1) = 0 |

211 | * ob2(2) = 1 |

212 | * ob2(3) = 2 |

213 | * ob2(4) = 2 |

214 | * ob2(5) = 3 |

215 | * ... and so on. |

216 | */ |

217 | #define order_base_2(n) \ |

218 | ( \ |

219 | __builtin_constant_p(n) ? ( \ |

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

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

222 | __order_base_2(n) \ |

223 | ) |

224 | |

225 | static inline __attribute__((const)) |

226 | int __bits_per(unsigned long n) |

227 | { |

228 | if (n < 2) |

229 | return 1; |

230 | if (is_power_of_2(n)) |

231 | return order_base_2(n) + 1; |

232 | return order_base_2(n); |

233 | } |

234 | |

235 | /** |

236 | * bits_per - calculate the number of bits required for the argument |

237 | * @n: parameter |

238 | * |

239 | * This is constant-capable and can be used for compile time |

240 | * initializations, e.g bitfields. |

241 | * |

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

243 | * bf(0) = 1 |

244 | * bf(1) = 1 |

245 | * bf(2) = 2 |

246 | * bf(3) = 2 |

247 | * bf(4) = 3 |

248 | * ... and so on. |

249 | */ |

250 | #define bits_per(n) \ |

251 | ( \ |

252 | __builtin_constant_p(n) ? ( \ |

253 | ((n) == 0 || (n) == 1) \ |

254 | ? 1 : ilog2(n) + 1 \ |

255 | ) : \ |

256 | __bits_per(n) \ |

257 | ) |

258 | #endif /* _LINUX_LOG2_H */ |

259 |