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target/i386: implement special cases for fxtract

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The implementation of the fxtract instruction treats all nonzero
operands as normal numbers, so yielding incorrect results for invalid
formats, infinities, NaNs and subnormal and pseudo-denormal operands.
Implement appropriate handling of all those cases.

Backports commit c415f2c58296d86e9abb7e4a133111acf7031da3 from qemu
This commit is contained in:
Joseph Myers 2020-06-15 13:02:22 -04:00 committed by Lioncash
parent 7373942623
commit 18fc17ca25
1 changed files with 24 additions and 1 deletions
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25
qemu/target/i386/fpu_helper.c
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@ -733,10 +733,33 @@ void helper_fxtract(CPUX86State *env)
&env->fp_status);
fpush(env);
ST0 = temp.d;
} else if (floatx80_invalid_encoding(ST0)) {
float_raise(float_flag_invalid, &env->fp_status);
ST0 = floatx80_default_nan(&env->fp_status);
fpush(env);
ST0 = ST1;
} else if (floatx80_is_any_nan(ST0)) {
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);
}
fpush(env);
ST0 = ST1;
} else if (floatx80_is_infinity(ST0)) {
fpush(env);
ST0 = ST1;
ST1 = floatx80_infinity;
} else {
int expdif;
expdif = EXPD(temp) - EXPBIAS;
if (EXPD(temp) == 0) {
int shift = clz64(temp.l.lower);
temp.l.lower <<= shift;
expdif = 1 - EXPBIAS - shift;
float_raise(float_flag_input_denormal, &env->fp_status);
} else {
expdif = EXPD(temp) - EXPBIAS;
}
/* DP exponent bias */
ST0 = int32_to_floatx80(expdif, &env->fp_status);
fpush(env);