| /* SPDX-License-Identifier: GPL-2.0-or-later */ |
| /* Integer base 2 logarithm calculation |
| * |
| * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. |
| * Written by David Howells (dhowells@redhat.com) |
| */ |
| |
| #pragma once |
| #include <stdint.h> |
| |
| /* from linux/asm-generic/bitops/{fls,fls64}.h - could later be enhanced |
| * with architecture specific optimized versions */ |
| |
| /** |
| * fls - find last (most-significant) bit set |
| * @x: the word to search |
| * |
| * This is defined the same way as ffs. |
| * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. |
| */ |
| static inline __attribute__((always_inline)) int fls(unsigned int x) |
| { |
| int r = 32; |
| |
| if (!x) |
| return 0; |
| if (!(x & 0xffff0000u)) { |
| x <<= 16; |
| r -= 16; |
| } |
| if (!(x & 0xff000000u)) { |
| x <<= 8; |
| r -= 8; |
| } |
| if (!(x & 0xf0000000u)) { |
| x <<= 4; |
| r -= 4; |
| } |
| if (!(x & 0xc0000000u)) { |
| x <<= 2; |
| r -= 2; |
| } |
| if (!(x & 0x80000000u)) { |
| x <<= 1; |
| r -= 1; |
| } |
| return r; |
| } |
| |
| /** |
| * fls64 - find last set bit in a 64-bit word |
| * @x: the word to search |
| * |
| * This is defined in a similar way as the libc and compiler builtin |
| * ffsll, but returns the position of the most significant set bit. |
| * |
| * fls64(value) returns 0 if value is 0 or the position of the last |
| * set bit if value is nonzero. The last (most significant) bit is |
| * at position 64. |
| */ |
| static inline __attribute__((always_inline)) int fls64(uint64_t x) |
| { |
| uint32_t h = x >> 32; |
| if (h) |
| return fls(h) + 32; |
| return fls(x); |
| } |
| |
| /* |
| * non-constant log of base 2 calculators |
| * - the arch may override these in asm/bitops.h if they can be implemented |
| * more efficiently than using fls() and fls64() |
| * - the arch is not required to handle n==0 if implementing the fallback |
| */ |
| #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |
| static inline __attribute__((const)) |
| int __ilog2_u32(uint32_t n) |
| { |
| return fls(n) - 1; |
| } |
| #endif |
| |
| #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |
| static inline __attribute__((const)) |
| int __ilog2_u64(uint64_t n) |
| { |
| return fls64(n) - 1; |
| } |
| #endif |
| |
| /** |
| * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value |
| * @n: parameter |
| * |
| * Use this where sparse expects a true constant expression, e.g. for array |
| * indices. |
| */ |
| #define const_ilog2(n) \ |
| ( \ |
| __builtin_constant_p(n) ? ( \ |
| (n) < 2 ? 0 : \ |
| (n) & (1ULL << 63) ? 63 : \ |
| (n) & (1ULL << 62) ? 62 : \ |
| (n) & (1ULL << 61) ? 61 : \ |
| (n) & (1ULL << 60) ? 60 : \ |
| (n) & (1ULL << 59) ? 59 : \ |
| (n) & (1ULL << 58) ? 58 : \ |
| (n) & (1ULL << 57) ? 57 : \ |
| (n) & (1ULL << 56) ? 56 : \ |
| (n) & (1ULL << 55) ? 55 : \ |
| (n) & (1ULL << 54) ? 54 : \ |
| (n) & (1ULL << 53) ? 53 : \ |
| (n) & (1ULL << 52) ? 52 : \ |
| (n) & (1ULL << 51) ? 51 : \ |
| (n) & (1ULL << 50) ? 50 : \ |
| (n) & (1ULL << 49) ? 49 : \ |
| (n) & (1ULL << 48) ? 48 : \ |
| (n) & (1ULL << 47) ? 47 : \ |
| (n) & (1ULL << 46) ? 46 : \ |
| (n) & (1ULL << 45) ? 45 : \ |
| (n) & (1ULL << 44) ? 44 : \ |
| (n) & (1ULL << 43) ? 43 : \ |
| (n) & (1ULL << 42) ? 42 : \ |
| (n) & (1ULL << 41) ? 41 : \ |
| (n) & (1ULL << 40) ? 40 : \ |
| (n) & (1ULL << 39) ? 39 : \ |
| (n) & (1ULL << 38) ? 38 : \ |
| (n) & (1ULL << 37) ? 37 : \ |
| (n) & (1ULL << 36) ? 36 : \ |
| (n) & (1ULL << 35) ? 35 : \ |
| (n) & (1ULL << 34) ? 34 : \ |
| (n) & (1ULL << 33) ? 33 : \ |
| (n) & (1ULL << 32) ? 32 : \ |
| (n) & (1ULL << 31) ? 31 : \ |
| (n) & (1ULL << 30) ? 30 : \ |
| (n) & (1ULL << 29) ? 29 : \ |
| (n) & (1ULL << 28) ? 28 : \ |
| (n) & (1ULL << 27) ? 27 : \ |
| (n) & (1ULL << 26) ? 26 : \ |
| (n) & (1ULL << 25) ? 25 : \ |
| (n) & (1ULL << 24) ? 24 : \ |
| (n) & (1ULL << 23) ? 23 : \ |
| (n) & (1ULL << 22) ? 22 : \ |
| (n) & (1ULL << 21) ? 21 : \ |
| (n) & (1ULL << 20) ? 20 : \ |
| (n) & (1ULL << 19) ? 19 : \ |
| (n) & (1ULL << 18) ? 18 : \ |
| (n) & (1ULL << 17) ? 17 : \ |
| (n) & (1ULL << 16) ? 16 : \ |
| (n) & (1ULL << 15) ? 15 : \ |
| (n) & (1ULL << 14) ? 14 : \ |
| (n) & (1ULL << 13) ? 13 : \ |
| (n) & (1ULL << 12) ? 12 : \ |
| (n) & (1ULL << 11) ? 11 : \ |
| (n) & (1ULL << 10) ? 10 : \ |
| (n) & (1ULL << 9) ? 9 : \ |
| (n) & (1ULL << 8) ? 8 : \ |
| (n) & (1ULL << 7) ? 7 : \ |
| (n) & (1ULL << 6) ? 6 : \ |
| (n) & (1ULL << 5) ? 5 : \ |
| (n) & (1ULL << 4) ? 4 : \ |
| (n) & (1ULL << 3) ? 3 : \ |
| (n) & (1ULL << 2) ? 2 : \ |
| 1) : \ |
| -1) |
| |
| /** |
| * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value |
| * @n: parameter |
| * |
| * constant-capable log of base 2 calculation |
| * - this can be used to initialise global variables from constant data, hence |
| * the massive ternary operator construction |
| * |
| * selects the appropriately-sized optimised version depending on sizeof(n) |
| */ |
| #define ilog2(n) \ |
| ( \ |
| __builtin_constant_p(n) ? \ |
| const_ilog2(n) : \ |
| (sizeof(n) <= 4) ? \ |
| __ilog2_u32(n) : \ |
| __ilog2_u64(n) \ |
| ) |