Commit f540166b authored by Richard Henderson's avatar Richard Henderson Committed by Blue Swirl
Browse files

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



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: default avatarRichard Henderson <rth@twiddle.net>
Signed-off-by: default avatarBlue Swirl <blauwirbel@gmail.com>
parent be96bd3f

configure

+20 −0
Original line number Diff line number Diff line
@@ -3150,6 +3150,22 @@ if compile_prog "" "" ; then 
    cpuid_h=yes

fi



########################################

# check if __[u]int128_t is usable.



int128=no

cat > $TMPC << EOF

__int128_t a;

__uint128_t b;

int main (void) {

  a = a + b;

  b = a * b;

  return 0;

}

EOF

if compile_prog "" "" ; then

    int128=yes

fi



##########################################

# End of CC checks
@@ -3692,6 +3708,10 @@ if test "$cpuid_h" = "yes" ; then 
  echo "CONFIG_CPUID_H=y" >> $config_host_mak

fi



if test "$int128" = "yes" ; then

  echo "CONFIG_INT128=y" >> $config_host_mak

fi



if test "$glusterfs" = "yes" ; then

  echo "CONFIG_GLUSTERFS=y" >> $config_host_mak

fi

include/qemu/host-utils.h

+8 −9
Original line number Diff line number Diff line
@@ -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);

util/host-utils.c

+2 −2
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ 
//#define DEBUG_MULDIV



/* Long integer helpers */

#if !defined(__x86_64__)

#ifndef CONFIG_INT128

static void add128 (uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b)

{

    *plow += a;
@@ -102,4 +102,4 @@ void muls64 (uint64_t *plow, uint64_t *phigh, int64_t a, int64_t b) 
           a, b, *phigh, *plow);

#endif

}

#endif /* !defined(__x86_64__) */
 
#endif /* !CONFIG_INT128 */