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fpu/softfloat: check for Inf / x or 0 / x before /0 

The re-factoring of div_floats changed the order of checking meaning
an operation like -inf/0 erroneously raises the divbyzero flag.
IEEE-754 (2008) specifies this should only occur for operations on
finite operands.

We fix this by moving the check on the dividend being Inf/0 to before
the divisor is zero check.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180416135442.30606-1-alex.bennee@linaro.org
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Reviewed-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Tested-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Alex Bennée 2018-04-16 14:54:42 +01:00 committed by Peter Maydell
parent 2a6b5372d7
commit 9cb4e398c2
1 changed files with 5 additions and 5 deletions
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10
fpu/softfloat.c
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@ -1146,6 +1146,11 @@ static FloatParts div_floats(FloatParts a, FloatParts b, float_status *s)
a.cls = float_class_dnan;
return a;
}
/* Inf / x or 0 / x */
if (a.cls == float_class_inf || a.cls == float_class_zero) {
a.sign = sign;
return a;
}
/* Div 0 => Inf */
if (b.cls == float_class_zero) {
s->float_exception_flags |= float_flag_divbyzero;
@ -1153,11 +1158,6 @@ static FloatParts div_floats(FloatParts a, FloatParts b, float_status *s)
a.sign = sign;
return a;
}
/* Inf / x or 0 / x */
if (a.cls == float_class_inf || a.cls == float_class_zero) {
a.sign = sign;
return a;
}
/* Div by Inf */
if (b.cls == float_class_inf) {
a.cls = float_class_zero;