log2.h

Go to the documentation of this file.

/* 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_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);
}
 
#define ilog2(n)                \
(                       \
    (sizeof(n) <= 4) ?          \
    __ilog2_u32(n) :            \
    __ilog2_u64(n)              \
 )
 
#define roundup_pow_of_two(n)           \
(                       \
    __builtin_constant_p(n) ? (     \
        (n == 1) ? 1 :          \
        (1UL << (ilog2((n) - 1) + 1))   \
                   ) :      \
    __roundup_pow_of_two(n)         \
 )
 
#define rounddown_pow_of_two(n)         \
(                       \
    __builtin_constant_p(n) ? (     \
        (n == 1) ? 0 :          \
        (1UL << ilog2(n))) :        \
    __rounddown_pow_of_two(n)       \
 )
 
#define order_base_2(n) ilog2(roundup_pow_of_two(n))
 
#endif /* _LINUX_LOG2_H */