mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-27 19:29:37 +00:00
![Jakub Jelinek](/assets/img/avatar_default.png)
As discussed in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 the const_ilog2 macro generates a lot of code which interferes badly with GCC inlining heuristics, until it can be proven that the ilog2 argument can or can't be simplified into a constant. It can be expressed using __builtin_clzll builtin which is supported by GCC 3.4 and later and when used only in the __builtin_constant_p guarded code it ought to always fold back to a constant. Other compilers support the same builtin for many years too. Other option would be to change the const_ilog2 macro, though as the description says it is meant to be used also in C constant expressions, and while GCC will fold it to constant with constant argument even in those, perhaps it is better to avoid using extensions in that case. [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20201120125154.GB3040@hirez.programming.kicks-ass.net Link: https://lkml.kernel.org/r/20201021132718.GB2176@tucnak Signed-off-by: Jakub Jelinek <jakub@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
258 lines
6.2 KiB
C
258 lines
6.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
|
|
/* Integer base 2 logarithm calculation
|
|
*
|
|
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
|
|
* Written by David Howells (dhowells@redhat.com)
|
|
*/
|
|
|
|
#ifndef _LINUX_LOG2_H
|
|
#define _LINUX_LOG2_H
|
|
|
|
#include <linux/types.h>
|
|
#include <linux/bitops.h>
|
|
|
|
/*
|
|
* 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
|
|
|
|
/**
|
|
* is_power_of_2() - check if a value is a power of two
|
|
* @n: the value to check
|
|
*
|
|
* Determine whether some value is a power of two, where zero is
|
|
* *not* considered a power of two.
|
|
* Return: true if @n is a power of 2, otherwise false.
|
|
*/
|
|
static inline __attribute__((const))
|
|
bool is_power_of_2(unsigned long n)
|
|
{
|
|
return (n != 0 && ((n & (n - 1)) == 0));
|
|
}
|
|
|
|
/**
|
|
* __roundup_pow_of_two() - round up to nearest power of two
|
|
* @n: value to round up
|
|
*/
|
|
static inline __attribute__((const))
|
|
unsigned long __roundup_pow_of_two(unsigned long n)
|
|
{
|
|
return 1UL << fls_long(n - 1);
|
|
}
|
|
|
|
/**
|
|
* __rounddown_pow_of_two() - round down to nearest power of two
|
|
* @n: value to round down
|
|
*/
|
|
static inline __attribute__((const))
|
|
unsigned long __rounddown_pow_of_two(unsigned long n)
|
|
{
|
|
return 1UL << (fls_long(n) - 1);
|
|
}
|
|
|
|
/**
|
|
* const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
|
|
* @n: parameter
|
|
*
|
|
* Use this where sparse expects a true constant expression, e.g. for array
|
|
* indices.
|
|
*/
|
|
#define const_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) : \
|
|
-1)
|
|
|
|
/**
|
|
* ilog2 - log 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 : \
|
|
63 - __builtin_clzll(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) ? ( \
|
|
(1UL << ilog2(n))) : \
|
|
__rounddown_pow_of_two(n) \
|
|
)
|
|
|
|
static inline __attribute_const__
|
|
int __order_base_2(unsigned long n)
|
|
{
|
|
return n > 1 ? ilog2(n - 1) + 1 : 0;
|
|
}
|
|
|
|
/**
|
|
* 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) \
|
|
( \
|
|
__builtin_constant_p(n) ? ( \
|
|
((n) == 0 || (n) == 1) ? 0 : \
|
|
ilog2((n) - 1) + 1) : \
|
|
__order_base_2(n) \
|
|
)
|
|
|
|
static inline __attribute__((const))
|
|
int __bits_per(unsigned long n)
|
|
{
|
|
if (n < 2)
|
|
return 1;
|
|
if (is_power_of_2(n))
|
|
return order_base_2(n) + 1;
|
|
return order_base_2(n);
|
|
}
|
|
|
|
/**
|
|
* bits_per - calculate the number of bits required for the argument
|
|
* @n: parameter
|
|
*
|
|
* This is constant-capable and can be used for compile time
|
|
* initializations, e.g bitfields.
|
|
*
|
|
* The first few values calculated by this routine:
|
|
* bf(0) = 1
|
|
* bf(1) = 1
|
|
* bf(2) = 2
|
|
* bf(3) = 2
|
|
* bf(4) = 3
|
|
* ... and so on.
|
|
*/
|
|
#define bits_per(n) \
|
|
( \
|
|
__builtin_constant_p(n) ? ( \
|
|
((n) == 0 || (n) == 1) \
|
|
? 1 : ilog2(n) + 1 \
|
|
) : \
|
|
__bits_per(n) \
|
|
)
|
|
#endif /* _LINUX_LOG2_H */
|