Make ARCH_HAS_FAST_MULTIPLIER a real config variable

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>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 778178f4c7d132c15f4f7700b0ad31a20ea7d24b..36327438caf0daffe826df5f4ad992885dd68cd8 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index afcd35d331de6348071f65ab52e373353e225786..cfe3b954d5e41cbd96be1fdb147c164b63581814 100644 (file)
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -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>

diff --git a/lib/Kconfig b/lib/Kconfig
index a5ce0c7f6c302058da57fe19bda51b9286cdd883..54cf309a92a5ed7c8d4af783bd8811d0b706dfd6 100644 (file)
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -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

diff --git a/lib/hweight.c b/lib/hweight.c
index b7d81ba143d13e01db3d6b92ea171c094bb7a1c6..9a5c1f2215585f35a8eea43eedd2566a6f459231 100644 (file)
--- a/lib/hweight.c
+++ b/lib/hweight.c
@@ -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;

diff --git a/lib/string.c b/lib/string.c
index 992bf30af7595f2cbc9b385c24a06e6990dd2c49..f3c6ff596414e6f9bd1cf58071fadfd4c7a31b35 100644 (file)
--- a/lib/string.c
+++ b/lib/string.c
@@ -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