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175 lines
4.5 KiB
175 lines
4.5 KiB
/* SPDX-License-Identifier: GPL-2.0-or-later */ |
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/* Integer base 2 logarithm calculation |
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* |
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* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. |
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* Written by David Howells ([email protected]) |
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*/ |
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#ifndef _TOOLS_LINUX_LOG2_H |
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#define _TOOLS_LINUX_LOG2_H |
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#include <linux/bitops.h> |
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#include <linux/types.h> |
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/* |
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* non-constant log of base 2 calculators |
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* - the arch may override these in asm/bitops.h if they can be implemented |
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* more efficiently than using fls() and fls64() |
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* - the arch is not required to handle n==0 if implementing the fallback |
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*/ |
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static inline __attribute__((const)) |
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int __ilog2_u32(u32 n) |
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{ |
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return fls(n) - 1; |
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} |
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static inline __attribute__((const)) |
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int __ilog2_u64(u64 n) |
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{ |
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return fls64(n) - 1; |
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} |
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/* |
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* Determine whether some value is a power of two, where zero is |
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* *not* considered a power of two. |
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*/ |
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static inline __attribute__((const)) |
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bool is_power_of_2(unsigned long n) |
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{ |
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return (n != 0 && ((n & (n - 1)) == 0)); |
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} |
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/* |
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* round up to nearest power of two |
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*/ |
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static inline __attribute__((const)) |
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unsigned long __roundup_pow_of_two(unsigned long n) |
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{ |
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return 1UL << fls_long(n - 1); |
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} |
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/* |
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* round down to nearest power of two |
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*/ |
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static inline __attribute__((const)) |
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unsigned long __rounddown_pow_of_two(unsigned long n) |
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{ |
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return 1UL << (fls_long(n) - 1); |
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} |
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/** |
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* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value |
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* @n - parameter |
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* |
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* constant-capable log of base 2 calculation |
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* - this can be used to initialise global variables from constant data, hence |
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* the massive ternary operator construction |
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* |
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* selects the appropriately-sized optimised version depending on sizeof(n) |
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*/ |
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#define ilog2(n) \ |
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( \ |
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__builtin_constant_p(n) ? ( \ |
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(n) < 2 ? 0 : \ |
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(n) & (1ULL << 63) ? 63 : \ |
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(n) & (1ULL << 62) ? 62 : \ |
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(n) & (1ULL << 61) ? 61 : \ |
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(n) & (1ULL << 60) ? 60 : \ |
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(n) & (1ULL << 59) ? 59 : \ |
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(n) & (1ULL << 58) ? 58 : \ |
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(n) & (1ULL << 57) ? 57 : \ |
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(n) & (1ULL << 56) ? 56 : \ |
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(n) & (1ULL << 55) ? 55 : \ |
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(n) & (1ULL << 54) ? 54 : \ |
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(n) & (1ULL << 53) ? 53 : \ |
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(n) & (1ULL << 52) ? 52 : \ |
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(n) & (1ULL << 51) ? 51 : \ |
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(n) & (1ULL << 50) ? 50 : \ |
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(n) & (1ULL << 49) ? 49 : \ |
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(n) & (1ULL << 48) ? 48 : \ |
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(n) & (1ULL << 47) ? 47 : \ |
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(n) & (1ULL << 46) ? 46 : \ |
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(n) & (1ULL << 45) ? 45 : \ |
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(n) & (1ULL << 44) ? 44 : \ |
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(n) & (1ULL << 43) ? 43 : \ |
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(n) & (1ULL << 42) ? 42 : \ |
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(n) & (1ULL << 41) ? 41 : \ |
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(n) & (1ULL << 40) ? 40 : \ |
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(n) & (1ULL << 39) ? 39 : \ |
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(n) & (1ULL << 38) ? 38 : \ |
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(n) & (1ULL << 37) ? 37 : \ |
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(n) & (1ULL << 36) ? 36 : \ |
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(n) & (1ULL << 35) ? 35 : \ |
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(n) & (1ULL << 34) ? 34 : \ |
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(n) & (1ULL << 33) ? 33 : \ |
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(n) & (1ULL << 32) ? 32 : \ |
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(n) & (1ULL << 31) ? 31 : \ |
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(n) & (1ULL << 30) ? 30 : \ |
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(n) & (1ULL << 29) ? 29 : \ |
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(n) & (1ULL << 28) ? 28 : \ |
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(n) & (1ULL << 27) ? 27 : \ |
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(n) & (1ULL << 26) ? 26 : \ |
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(n) & (1ULL << 25) ? 25 : \ |
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(n) & (1ULL << 24) ? 24 : \ |
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(n) & (1ULL << 23) ? 23 : \ |
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(n) & (1ULL << 22) ? 22 : \ |
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(n) & (1ULL << 21) ? 21 : \ |
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(n) & (1ULL << 20) ? 20 : \ |
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(n) & (1ULL << 19) ? 19 : \ |
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(n) & (1ULL << 18) ? 18 : \ |
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(n) & (1ULL << 17) ? 17 : \ |
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(n) & (1ULL << 16) ? 16 : \ |
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(n) & (1ULL << 15) ? 15 : \ |
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(n) & (1ULL << 14) ? 14 : \ |
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(n) & (1ULL << 13) ? 13 : \ |
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(n) & (1ULL << 12) ? 12 : \ |
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(n) & (1ULL << 11) ? 11 : \ |
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(n) & (1ULL << 10) ? 10 : \ |
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(n) & (1ULL << 9) ? 9 : \ |
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(n) & (1ULL << 8) ? 8 : \ |
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(n) & (1ULL << 7) ? 7 : \ |
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(n) & (1ULL << 6) ? 6 : \ |
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(n) & (1ULL << 5) ? 5 : \ |
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(n) & (1ULL << 4) ? 4 : \ |
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(n) & (1ULL << 3) ? 3 : \ |
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(n) & (1ULL << 2) ? 2 : \ |
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1 ) : \ |
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(sizeof(n) <= 4) ? \ |
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__ilog2_u32(n) : \ |
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__ilog2_u64(n) \ |
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) |
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/** |
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* roundup_pow_of_two - round the given value up to nearest power of two |
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* @n - parameter |
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* |
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* round the given value up to the nearest power of two |
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* - the result is undefined when n == 0 |
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* - this can be used to initialise global variables from constant data |
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*/ |
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#define roundup_pow_of_two(n) \ |
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( \ |
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__builtin_constant_p(n) ? ( \ |
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(n == 1) ? 1 : \ |
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(1UL << (ilog2((n) - 1) + 1)) \ |
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) : \ |
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__roundup_pow_of_two(n) \ |
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) |
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/** |
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* rounddown_pow_of_two - round the given value down to nearest power of two |
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* @n - parameter |
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* |
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* round the given value down to the nearest power of two |
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* - the result is undefined when n == 0 |
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* - this can be used to initialise global variables from constant data |
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*/ |
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#define rounddown_pow_of_two(n) \ |
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( \ |
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__builtin_constant_p(n) ? ( \ |
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(1UL << ilog2(n))) : \ |
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__rounddown_pow_of_two(n) \ |
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) |
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#endif /* _TOOLS_LINUX_LOG2_H */
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