209 lines
5.3 KiB
C
209 lines
5.3 KiB
C
/* 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
|
|
*/
|
|
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);
|
|
}
|
|
|
|
/**
|
|
* 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) < 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) \
|
|
)
|
|
|
|
/**
|
|
* 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.
|
|
*/
|
|
|
|
#define order_base_2(n) ilog2(roundup_pow_of_two(n))
|
|
|
|
#endif /* _LINUX_LOG2_H */
|