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host-utils: Use __int128_t for mul[us]64

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Replace some x86_64 specific inline assembly with something that
all 64-bit hosts ought to optimize well.  At worst this becomes
a call to the gcc __multi3 routine, which is no worse than our
implementation in util/host-utils.c.

With gcc 4.7, we get identical code generation for x86_64.  We
now get native multiplication on ia64 and s390x hosts.  With minor
improvements to gcc we can get it for ppc64 as well.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
This commit is contained in:
Richard Henderson 2013-02-16 12:46:59 -08:00 • committed by Blue Swirl
parent be96bd3fbf
commit f540166b7d
3 changed files with 30 additions and 11 deletions
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17
include/qemu/host-utils.h
View file

@ -28,22 +28,21 @@
#include "qemu/compiler.h" /* QEMU_GNUC_PREREQ */
#include <limits.h>
#if defined(__x86_64__)
#define __HAVE_FAST_MULU64__
#ifdef CONFIG_INT128
static inline void mulu64(uint64_t *plow, uint64_t *phigh,
uint64_t a, uint64_t b)
{
__asm__ ("mul %0\n\t"
: "=d" (*phigh), "=a" (*plow)
: "a" (a), "0" (b));
__uint128_t r = (__uint128_t)a * b;
*plow = r;
*phigh = r >> 64;
}
#define __HAVE_FAST_MULS64__
static inline void muls64(uint64_t *plow, uint64_t *phigh,
int64_t a, int64_t b)
{
__asm__ ("imul %0\n\t"
: "=d" (*phigh), "=a" (*plow)
: "a" (a), "0" (b));
__int128_t r = (__int128_t)a * b;
*plow = r;
*phigh = r >> 64;
}
#else
void muls64(uint64_t *phigh, uint64_t *plow, int64_t a, int64_t b);