Harald Welte | 7101ca2 | 2020-12-04 21:44:44 +0100 | [diff] [blame] | 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 | #pragma once |
Harald Welte | c172d9f | 2020-12-06 15:13:09 +0100 | [diff] [blame] | 9 | #include <stdint.h> |
Harald Welte | 622cda3 | 2020-12-06 14:37:18 +0100 | [diff] [blame] | 10 | |
| 11 | /* from linux/asm-generic/bitops/{fls,fls64}.h - could later be enhanced |
| 12 | * with architecture specific optimized versions */ |
| 13 | |
| 14 | /** |
| 15 | * fls - find last (most-significant) bit set |
| 16 | * @x: the word to search |
| 17 | * |
| 18 | * This is defined the same way as ffs. |
| 19 | * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. |
| 20 | */ |
Harald Welte | 7fc88b3 | 2020-12-06 15:45:11 +0100 | [diff] [blame] | 21 | static inline __attribute__((always_inline)) int fls(unsigned int x) |
Harald Welte | 622cda3 | 2020-12-06 14:37:18 +0100 | [diff] [blame] | 22 | { |
| 23 | int r = 32; |
| 24 | |
| 25 | if (!x) |
| 26 | return 0; |
| 27 | if (!(x & 0xffff0000u)) { |
| 28 | x <<= 16; |
| 29 | r -= 16; |
| 30 | } |
| 31 | if (!(x & 0xff000000u)) { |
| 32 | x <<= 8; |
| 33 | r -= 8; |
| 34 | } |
| 35 | if (!(x & 0xf0000000u)) { |
| 36 | x <<= 4; |
| 37 | r -= 4; |
| 38 | } |
| 39 | if (!(x & 0xc0000000u)) { |
| 40 | x <<= 2; |
| 41 | r -= 2; |
| 42 | } |
| 43 | if (!(x & 0x80000000u)) { |
| 44 | x <<= 1; |
| 45 | r -= 1; |
| 46 | } |
| 47 | return r; |
| 48 | } |
| 49 | |
| 50 | /** |
| 51 | * fls64 - find last set bit in a 64-bit word |
| 52 | * @x: the word to search |
| 53 | * |
| 54 | * This is defined in a similar way as the libc and compiler builtin |
| 55 | * ffsll, but returns the position of the most significant set bit. |
| 56 | * |
| 57 | * fls64(value) returns 0 if value is 0 or the position of the last |
| 58 | * set bit if value is nonzero. The last (most significant) bit is |
| 59 | * at position 64. |
| 60 | */ |
Harald Welte | 7fc88b3 | 2020-12-06 15:45:11 +0100 | [diff] [blame] | 61 | static inline __attribute__((always_inline)) int fls64(uint64_t x) |
Harald Welte | 622cda3 | 2020-12-06 14:37:18 +0100 | [diff] [blame] | 62 | { |
Harald Welte | c172d9f | 2020-12-06 15:13:09 +0100 | [diff] [blame] | 63 | uint32_t h = x >> 32; |
Harald Welte | 622cda3 | 2020-12-06 14:37:18 +0100 | [diff] [blame] | 64 | if (h) |
| 65 | return fls(h) + 32; |
| 66 | return fls(x); |
| 67 | } |
Harald Welte | 7101ca2 | 2020-12-04 21:44:44 +0100 | [diff] [blame] | 68 | |
| 69 | /* |
| 70 | * non-constant log of base 2 calculators |
| 71 | * - the arch may override these in asm/bitops.h if they can be implemented |
| 72 | * more efficiently than using fls() and fls64() |
| 73 | * - the arch is not required to handle n==0 if implementing the fallback |
| 74 | */ |
| 75 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |
| 76 | static inline __attribute__((const)) |
| 77 | int __ilog2_u32(uint32_t n) |
| 78 | { |
| 79 | return fls(n) - 1; |
| 80 | } |
| 81 | #endif |
| 82 | |
| 83 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |
| 84 | static inline __attribute__((const)) |
| 85 | int __ilog2_u64(uint64_t n) |
| 86 | { |
| 87 | return fls64(n) - 1; |
| 88 | } |
| 89 | #endif |
| 90 | |
| 91 | /** |
| 92 | * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value |
| 93 | * @n: parameter |
| 94 | * |
| 95 | * Use this where sparse expects a true constant expression, e.g. for array |
| 96 | * indices. |
| 97 | */ |
| 98 | #define const_ilog2(n) \ |
| 99 | ( \ |
| 100 | __builtin_constant_p(n) ? ( \ |
| 101 | (n) < 2 ? 0 : \ |
| 102 | (n) & (1ULL << 63) ? 63 : \ |
| 103 | (n) & (1ULL << 62) ? 62 : \ |
| 104 | (n) & (1ULL << 61) ? 61 : \ |
| 105 | (n) & (1ULL << 60) ? 60 : \ |
| 106 | (n) & (1ULL << 59) ? 59 : \ |
| 107 | (n) & (1ULL << 58) ? 58 : \ |
| 108 | (n) & (1ULL << 57) ? 57 : \ |
| 109 | (n) & (1ULL << 56) ? 56 : \ |
| 110 | (n) & (1ULL << 55) ? 55 : \ |
| 111 | (n) & (1ULL << 54) ? 54 : \ |
| 112 | (n) & (1ULL << 53) ? 53 : \ |
| 113 | (n) & (1ULL << 52) ? 52 : \ |
| 114 | (n) & (1ULL << 51) ? 51 : \ |
| 115 | (n) & (1ULL << 50) ? 50 : \ |
| 116 | (n) & (1ULL << 49) ? 49 : \ |
| 117 | (n) & (1ULL << 48) ? 48 : \ |
| 118 | (n) & (1ULL << 47) ? 47 : \ |
| 119 | (n) & (1ULL << 46) ? 46 : \ |
| 120 | (n) & (1ULL << 45) ? 45 : \ |
| 121 | (n) & (1ULL << 44) ? 44 : \ |
| 122 | (n) & (1ULL << 43) ? 43 : \ |
| 123 | (n) & (1ULL << 42) ? 42 : \ |
| 124 | (n) & (1ULL << 41) ? 41 : \ |
| 125 | (n) & (1ULL << 40) ? 40 : \ |
| 126 | (n) & (1ULL << 39) ? 39 : \ |
| 127 | (n) & (1ULL << 38) ? 38 : \ |
| 128 | (n) & (1ULL << 37) ? 37 : \ |
| 129 | (n) & (1ULL << 36) ? 36 : \ |
| 130 | (n) & (1ULL << 35) ? 35 : \ |
| 131 | (n) & (1ULL << 34) ? 34 : \ |
| 132 | (n) & (1ULL << 33) ? 33 : \ |
| 133 | (n) & (1ULL << 32) ? 32 : \ |
| 134 | (n) & (1ULL << 31) ? 31 : \ |
| 135 | (n) & (1ULL << 30) ? 30 : \ |
| 136 | (n) & (1ULL << 29) ? 29 : \ |
| 137 | (n) & (1ULL << 28) ? 28 : \ |
| 138 | (n) & (1ULL << 27) ? 27 : \ |
| 139 | (n) & (1ULL << 26) ? 26 : \ |
| 140 | (n) & (1ULL << 25) ? 25 : \ |
| 141 | (n) & (1ULL << 24) ? 24 : \ |
| 142 | (n) & (1ULL << 23) ? 23 : \ |
| 143 | (n) & (1ULL << 22) ? 22 : \ |
| 144 | (n) & (1ULL << 21) ? 21 : \ |
| 145 | (n) & (1ULL << 20) ? 20 : \ |
| 146 | (n) & (1ULL << 19) ? 19 : \ |
| 147 | (n) & (1ULL << 18) ? 18 : \ |
| 148 | (n) & (1ULL << 17) ? 17 : \ |
| 149 | (n) & (1ULL << 16) ? 16 : \ |
| 150 | (n) & (1ULL << 15) ? 15 : \ |
| 151 | (n) & (1ULL << 14) ? 14 : \ |
| 152 | (n) & (1ULL << 13) ? 13 : \ |
| 153 | (n) & (1ULL << 12) ? 12 : \ |
| 154 | (n) & (1ULL << 11) ? 11 : \ |
| 155 | (n) & (1ULL << 10) ? 10 : \ |
| 156 | (n) & (1ULL << 9) ? 9 : \ |
| 157 | (n) & (1ULL << 8) ? 8 : \ |
| 158 | (n) & (1ULL << 7) ? 7 : \ |
| 159 | (n) & (1ULL << 6) ? 6 : \ |
| 160 | (n) & (1ULL << 5) ? 5 : \ |
| 161 | (n) & (1ULL << 4) ? 4 : \ |
| 162 | (n) & (1ULL << 3) ? 3 : \ |
| 163 | (n) & (1ULL << 2) ? 2 : \ |
| 164 | 1) : \ |
| 165 | -1) |
| 166 | |
| 167 | /** |
| 168 | * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value |
| 169 | * @n: parameter |
| 170 | * |
| 171 | * constant-capable log of base 2 calculation |
| 172 | * - this can be used to initialise global variables from constant data, hence |
| 173 | * the massive ternary operator construction |
| 174 | * |
| 175 | * selects the appropriately-sized optimised version depending on sizeof(n) |
| 176 | */ |
| 177 | #define ilog2(n) \ |
| 178 | ( \ |
| 179 | __builtin_constant_p(n) ? \ |
| 180 | const_ilog2(n) : \ |
| 181 | (sizeof(n) <= 4) ? \ |
| 182 | __ilog2_u32(n) : \ |
| 183 | __ilog2_u64(n) \ |
| 184 | ) |