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target/i386: fix fscale handling of signaling NaN

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The implementation of the fscale instruction returns a NaN exponent
unchanged.  Fix it to return a quiet NaN when the provided exponent is
a signaling NaN.

Signed-off-by: Joseph Myers <joseph@codesourcery.com>
Message-Id: <alpine.DEB.2.21.2005070043330.18350@digraph.polyomino.org.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Joseph Myers 2020-05-07 00:44:14 +00:00 committed by Paolo Bonzini
parent c415f2c582
commit 0d48b43632
2 changed files with 41 additions and 0 deletions
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4
target/i386/fpu_helper.c
View File

@ -970,6 +970,10 @@ void helper_fscale(CPUX86State *env)
{
if (floatx80_is_any_nan(ST1)) {
ST0 = ST1;
if (floatx80_is_signaling_nan(ST0, &env->fp_status)) {
float_raise(float_flag_invalid, &env->fp_status);
ST0 = floatx80_silence_nan(ST0, &env->fp_status);
}
} else {
int n = floatx80_to_int32_round_to_zero(ST1, &env->fp_status);
ST0 = floatx80_scalbn(ST0, n, &env->fp_status);

37
tests/tcg/i386/test-i386-fscale.c Normal file
View File

@ -0,0 +1,37 @@
/* Test fscale instruction. */
#include <stdint.h>
#include <stdio.h>
union u {
struct { uint64_t sig; uint16_t sign_exp; } s;
long double ld;
};
volatile long double ld_res;
int isnan_ld(long double x)
{
union u tmp = { .ld = x };
return ((tmp.s.sign_exp & 0x7fff) == 0x7fff &&
(tmp.s.sig >> 63) != 0 &&
(tmp.s.sig << 1) != 0);
}
int issignaling_ld(long double x)
{
union u tmp = { .ld = x };
return isnan_ld(x) && (tmp.s.sig & UINT64_C(0x4000000000000000)) == 0;
}
int main(void)
{
int ret = 0;
__asm__ volatile ("fscale" : "=t" (ld_res) :
"0" (2.5L), "u" (__builtin_nansl("")));
if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) {
printf("FAIL: fscale snan\n");
ret = 1;
}
return ret;
}