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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141/* 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 <linux/types.h>#include <linux/bitops.h>
/* * deal with unrepresentable constant logarithms */int ____ilog2_NaN(void);
/* * 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_U32static inline __attribute__((const))int __ilog2_u32(u32 n){ return fls(n) - 1;}#endif
#ifndef CONFIG_ARCH_HAS_ILOG2_U64static 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) \( \ (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) ? ( \ (n == 1) ? 0 : \ (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. */
#define order_base_2(n) ilog2(roundup_pow_of_two(n))
#endif /* _LINUX_LOG2_H */