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Make ARCH_HAS_FAST_MULTIPLIER a real config variable

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It used to be an ad-hoc hack defined by the x86 version of
<asm/bitops.h> that enabled a couple of library routines to know whether
an integer multiply is faster than repeated shifts and additions.

This just makes it use the real Kconfig system instead, and makes x86
(which was the only architecture that did this) select the option.

NOTE! Even for x86, this really is kind of wrong.  If we cared, we would
probably not enable this for builds optimized for netburst (P4), where
shifts-and-adds are generally faster than multiplies.  This patch does
*not* change that kind of logic, though, it is purely a syntactic change
with no code changes.

This was triggered by the fact that we have other places that really
want to know "do I want to expand multiples by constants by hand or
not", particularly the hash generation code.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2014-09-13 11:14:53 -07:00
parent 186cec317e
commit 72d9310460
5 changed files with 8 additions and 6 deletions
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1
arch/x86/Kconfig
View File

@ -23,6 +23,7 @@ config X86
def_bool y
select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_HAS_FAST_MULTIPLIER
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_MIGHT_HAVE_PC_SERIO
select HAVE_AOUT if X86_32

2
arch/x86/include/asm/bitops.h
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@ -497,8 +497,6 @@ static __always_inline int fls64(__u64 x)
#include <asm-generic/bitops/sched.h>
#define ARCH_HAS_FAST_MULTIPLIER 1
#include <asm/arch_hweight.h>
#include <asm-generic/bitops/const_hweight.h>

3
lib/Kconfig
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@ -51,6 +51,9 @@ config PERCPU_RWSEM
config ARCH_USE_CMPXCHG_LOCKREF
bool
config ARCH_HAS_FAST_MULTIPLIER
bool
config CRC_CCITT
tristate "CRC-CCITT functions"
help

4
lib/hweight.c
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@ -11,7 +11,7 @@
unsigned int __sw_hweight32(unsigned int w)
{
#ifdef ARCH_HAS_FAST_MULTIPLIER
#ifdef CONFIG_ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x55555555;
w = (w & 0x33333333) + ((w >> 2) & 0x33333333);
w = (w + (w >> 4)) & 0x0f0f0f0f;
@ -49,7 +49,7 @@ unsigned long __sw_hweight64(__u64 w)
return __sw_hweight32((unsigned int)(w >> 32)) +
__sw_hweight32((unsigned int)w);
#elif BITS_PER_LONG == 64
#ifdef ARCH_HAS_FAST_MULTIPLIER
#ifdef CONFIG_ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x5555555555555555ul;
w = (w & 0x3333333333333333ul) + ((w >> 2) & 0x3333333333333333ul);
w = (w + (w >> 4)) & 0x0f0f0f0f0f0f0f0ful;

4
lib/string.c
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@ -807,9 +807,9 @@ void *memchr_inv(const void *start, int c, size_t bytes)
return check_bytes8(start, value, bytes);
value64 = value;
#if defined(ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
value64 *= 0x0101010101010101;
#elif defined(ARCH_HAS_FAST_MULTIPLIER)
#elif defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER)
value64 *= 0x01010101;
value64 |= value64 << 32;
#else