On Thu, May 07, 2020 at 12:43:30AM +0000, Joseph Myers wrote:
> 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.
>
> Signed-off-by: Joseph Myers <jos...@codesourcery.com>
> ---
> target/i386/fpu_helper.c | 25 +++++-
> tests/tcg/i386/test-i386-fxtract.c | 120 +++++++++++++++++++++++++++++
> 2 files changed, 144 insertions(+), 1 deletion(-)
> create mode 100644 tests/tcg/i386/test-i386-fxtract.c
>
> diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
> index 792a128a6d..71a696a863 100644
> --- a/target/i386/fpu_helper.c
> +++ b/target/i386/fpu_helper.c
> @@ -767,10 +767,33 @@ 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;
Coverity reports the following. It looks like a false positive
because floatx80_is_zero() would be true if both EXPD(temp) and
temp.l.lower were zero, but maybe I'm missing something.
________________________________________________________________________________________________________
*** CID 1429970: Integer handling issues (BAD_SHIFT)
/target/i386/fpu_helper.c: 922 in helper_fxtract()
916 ST1 = floatx80_infinity;
917 } else {
918 int expdif;
919
920 if (EXPD(temp) == 0) {
921 int shift = clz64(temp.l.lower);
>>> CID 1429970: Integer handling issues (BAD_SHIFT)
>>> In expression "temp.l.lower <<= shift", left shifting by more than 63
>>> bits has undefined behavior. The shift amount, "shift", is 64.
922 temp.l.lower <<= shift;
923 expdif = 1 - EXPBIAS - shift;
924 float_raise(float_flag_input_denormal, &env->fp_status);
925 } else {
926 expdif = EXPD(temp) - EXPBIAS;
927 }
> + 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);
--
Eduardo
