/* Integer base 2 logarithm calculation * * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. */ #ifndef _LINUX_LOG2_H #define _LINUX_LOG2_H #include #include #include #include /* * 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(u32 n) { return fls(n) - 1; } #endif #ifndef CONFIG_ARCH_HAS_ILOG2_U64 static inline __attribute__((const)) int __ilog2_u64(u64 n) { return fls64(n) - 1; } #endif /* * Determine whether some value is a power of two, where zero is * *not* considered a power of two. */ static inline __attribute__((const)) bool is_power_of_2(unsigned long n) { return (n != 0 && ((n & (n - 1)) == 0)); } /* * round up to nearest power of two */ static inline __attribute__((const)) unsigned long __roundup_pow_of_two(unsigned long n) { return 1UL << fls_long(n - 1); } /* * round down to nearest power of two */ static inline __attribute__((const)) unsigned long __rounddown_pow_of_two(unsigned long n) { return 1UL << (fls_long(n) - 1); } /** * ilog2 - log of 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) ? \ ((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) : \ (sizeof(n) <= 4) ? __ilog2_u32(n) : __ilog2_u64(n)) /** * roundup_pow_of_two - round the given value up to nearest power of two * @n - parameter * * round the given value up to the nearest power of two * - the result is undefined when n == 0 * - this can be used to initialise global variables from constant data */ #define roundup_pow_of_two(n) \ (__builtin_constant_p(n) ? \ ((n == 1) ? 1 : (1UL << (ilog2((n)-1) + 1))) : \ __roundup_pow_of_two(n)) /** * rounddown_pow_of_two - round the given value down to nearest power of two * @n - parameter * * round the given value down to the nearest power of two * - the result is undefined when n == 0 * - this can be used to initialise global variables from constant data */ #define rounddown_pow_of_two(n) \ (__builtin_constant_p(n) ? ((1UL << ilog2(n))) : \ __rounddown_pow_of_two(n)) /** * order_base_2 - calculate the (rounded up) base 2 order of the argument * @n: parameter * * The first few values calculated by this routine: * ob2(0) = 0 * ob2(1) = 0 * ob2(2) = 1 * ob2(3) = 2 * ob2(4) = 2 * ob2(5) = 3 * ... and so on. */ static inline __attribute_const__ int __order_base_2(unsigned long n) { return n > 1 ? ilog2(n - 1) + 1 : 0; } #define order_base_2(n) \ (__builtin_constant_p(n) ? \ (((n) == 0 || (n) == 1) ? 0 : ilog2((n)-1) + 1) : \ __order_base_2(n)) #endif /* _LINUX_LOG2_H */