log2.h

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/* Integer base 2 logarithm calculation
 *
 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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
 */
extern __attribute__((const, noreturn))
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)                \
(                       \
    __builtin_constant_p(n) ? (     \
        (n) < 1 ? ____ilog2_NaN() : \
        (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 :   \
        (n) & (1ULL <<  1) ?  1 :   \
        (n) & (1ULL <<  0) ?  0 :   \
        ____ilog2_NaN()         \
                   ) :      \
    (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) ? (     \
        (1UL << ilog2(n))) :        \
    __rounddown_pow_of_two(n)       \
 )

#define order_base_2(n) ilog2(roundup_pow_of_two(n))

#endif /* _LINUX_LOG2_H */