| Message ID | 20180417025328.25431-2-richard.henderson@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] fpu: Check for inf/x before x/0 | expand |
On 17 April 2018 at 03:53, Richard Henderson <richard.henderson@linaro.org> wrote: > 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. > I've applied Alex's fix to master for this, since it seems more straightforward. thanks -- PMM
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index fb8663f59e..ba6e654050 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -1146,15 +1146,20 @@ static FloatParts div_floats(FloatParts a, FloatParts b, float_status *s) a.cls = float_class_dnan; return a; } - /* Div 0 => Inf */ + /* Inf / x */ + if (a.cls == float_class_inf) { + a.sign = sign; + return a; + } + /* x / 0 => Inf */ if (b.cls == float_class_zero) { s->float_exception_flags |= float_flag_divbyzero; a.cls = float_class_inf; a.sign = sign; return a; } - /* Inf / x or 0 / x */ - if (a.cls == float_class_inf || a.cls == float_class_zero) { + /* 0 / x */ + if (a.cls == float_class_zero) { a.sign = sign; return a; }
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. Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de> Cc: Alex Bennée <alex.bennee@linaro.org> Cc: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- fpu/softfloat.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)