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host-utils: Improve mulu64 and muls64

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The new formulation makes better use of add-with-carry type insns
that the host may have.  Use gcc's sign adjustment trick to avoid
having to perform a 128-bit negation.

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 12:47:00 -08:00 committed by Blue Swirl
parent f540166b7d
commit ff7a1eb0a1
1 changed files with 38 additions and 54 deletions
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92
util/host-utils.c
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@ -27,79 +27,63 @@
#include <stdint.h>
#include "qemu/host-utils.h"
//#define DEBUG_MULDIV
/* Long integer helpers */
#ifndef CONFIG_INT128
static void add128 (uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b)
static inline void mul64(uint64_t *plow, uint64_t *phigh,
uint64_t a, uint64_t b)
{
*plow += a;
/* carry test */
if (*plow < a)
(*phigh)++;
*phigh += b;
}
typedef union {
uint64_t ll;
struct {
#ifdef HOST_WORDS_BIGENDIAN
uint32_t high, low;
#else
uint32_t low, high;
#endif
} l;
} LL;
LL rl, rm, rn, rh, a0, b0;
uint64_t c;
static void neg128 (uint64_t *plow, uint64_t *phigh)
{
*plow = ~*plow;
*phigh = ~*phigh;
add128(plow, phigh, 1, 0);
}
a0.ll = a;
b0.ll = b;
static void mul64 (uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b)
{
uint32_t a0, a1, b0, b1;
uint64_t v;
rl.ll = (uint64_t)a0.l.low * b0.l.low;
rm.ll = (uint64_t)a0.l.low * b0.l.high;
rn.ll = (uint64_t)a0.l.high * b0.l.low;
rh.ll = (uint64_t)a0.l.high * b0.l.high;
a0 = a;
a1 = a >> 32;
c = (uint64_t)rl.l.high + rm.l.low + rn.l.low;
rl.l.high = c;
c >>= 32;
c = c + rm.l.high + rn.l.high + rh.l.low;
rh.l.low = c;
rh.l.high += (uint32_t)(c >> 32);
b0 = b;
b1 = b >> 32;
v = (uint64_t)a0 * (uint64_t)b0;
*plow = v;
*phigh = 0;
v = (uint64_t)a0 * (uint64_t)b1;
add128(plow, phigh, v << 32, v >> 32);
v = (uint64_t)a1 * (uint64_t)b0;
add128(plow, phigh, v << 32, v >> 32);
v = (uint64_t)a1 * (uint64_t)b1;
*phigh += v;
*plow = rl.ll;
*phigh = rh.ll;
}
/* Unsigned 64x64 -> 128 multiplication */
void mulu64 (uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b)
{
mul64(plow, phigh, a, b);
#if defined(DEBUG_MULDIV)
printf("mulu64: 0x%016llx * 0x%016llx = 0x%016llx%016llx\n",
a, b, *phigh, *plow);
#endif
}
/* Signed 64x64 -> 128 multiplication */
void muls64 (uint64_t *plow, uint64_t *phigh, int64_t a, int64_t b)
{
int sa, sb;
uint64_t rh;
sa = (a < 0);
if (sa)
a = -a;
sb = (b < 0);
if (sb)
b = -b;
mul64(plow, phigh, a, b);
if (sa ^ sb) {
neg128(plow, phigh);
mul64(plow, &rh, a, b);
/* Adjust for signs. */
if (b < 0) {
rh -= a;
}
#if defined(DEBUG_MULDIV)
printf("muls64: 0x%016llx * 0x%016llx = 0x%016llx%016llx\n",
a, b, *phigh, *plow);
#endif
if (a < 0) {
rh -= b;
}
*phigh = rh;
}
#endif /* !CONFIG_INT128 */