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Fix rounding in f32.nearest / f64.nearest

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This commit is contained in:
Chris Fallin 2023-02-24 11:36:38 -08:00
parent 0f42e16446
commit 6dbdefc858
1 changed files with 37 additions and 2 deletions
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39
src/interp.rs
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@ -561,7 +561,28 @@ pub fn const_eval(
Some(ConstVal::F32(f32::from_bits(*a).trunc().to_bits()))
}
(Operator::F32Nearest, [ConstVal::F32(a)]) => {
Some(ConstVal::F32(f32::from_bits(*a).round().to_bits()))
// See
// https://github.com/paritytech/wasmi/blob/43ce25d47e26498b9372369345e75dc9632eca8f/crates/core/src/value.rs#L662
// for the origin of this algorithm.
//
// When https://github.com/rust-lang/rust/pull/95317 is
// resolved and the resulting API is stable, we can switch
// to that instead.
let a = f32::from_bits(*a);
let round = a.round();
let nearest = if a.fract().abs() != 0.5 {
round
} else {
let rem = round % 2.0;
if rem == 1.0 {
a.floor()
} else if rem == -1.0 {
a.ceil()
} else {
round
}
};
Some(ConstVal::F32(nearest.to_bits()))
}
(Operator::F32Sqrt, [ConstVal::F32(a)]) => {
Some(ConstVal::F32(f32::from_bits(*a).sqrt().to_bits()))
@ -604,7 +625,21 @@ pub fn const_eval(
Some(ConstVal::F64(f64::from_bits(*a).trunc().to_bits()))
}
(Operator::F64Nearest, [ConstVal::F64(a)]) => {
Some(ConstVal::F64(f64::from_bits(*a).round().to_bits()))
let a = f64::from_bits(*a);
let round = a.round();
let nearest = if a.fract().abs() != 0.5 {
round
} else {
let rem = round % 2.0;
if rem == 1.0 {
a.floor()
} else if rem == -1.0 {
a.ceil()
} else {
round
}
};
Some(ConstVal::F64(nearest.to_bits()))
}
(Operator::F64Sqrt, [ConstVal::F64(a)]) => {
Some(ConstVal::F64(f64::from_bits(*a).sqrt().to_bits()))