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Fix substract with borrow in FMA #252

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Jun 25, 2021
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Fix substract with borrow in FMA #252

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c18c704
Fix build failure with latest nightly
Jun 24, 2021
8f10cf5
Fix substract with borrow in FMA
Jun 22, 2021
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16 changes: 12 additions & 4 deletions src/math/fma.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -122,9 +122,9 @@ pub fn fma(x: f64, y: f64, z: f64) -> f64 {
rhi += zhi + (rlo < zlo) as u64;
} else {
/* r -= z */
let t = rlo;
rlo = rlo.wrapping_sub(zlo);
rhi = rhi.wrapping_sub(zhi.wrapping_sub((t < rlo) as u64));
let (res, borrow) = rlo.overflowing_sub(zlo);
rlo = res;
rhi = rhi.wrapping_sub(zhi.wrapping_add(borrow as u64));
if (rhi >> 63) != 0 {
rlo = (-(rlo as i64)) as u64;
rhi = (-(rhi as i64)) as u64 - (rlo != 0) as u64;
Expand Down Expand Up @@ -218,6 +218,14 @@ mod tests {
-0.00000000000000022204460492503126,
);

assert_eq!(fma(-0.992, -0.992, -0.992), -0.00793599999988632,);
assert_eq!(fma(-0.992, -0.992, -0.992), -0.007936000000000007,);
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This is the result from GNU libm

}

#[test]
fn fma_sbb() {
assert_eq!(
fma(-(1.0 - f64::EPSILON), f64::MIN, f64::MIN),
-3991680619069439e277
);
}
}
4 changes: 2 additions & 2 deletions src/math/pow.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -604,7 +604,7 @@ mod tests {

// Factoring -1 out:
// (negative anything ^ integer should be (-1 ^ integer) * (positive anything ^ integer))
&[POS_ZERO, NEG_ZERO, POS_ONE, NEG_ONE, POS_EVENS, NEG_EVENS]
(&[POS_ZERO, NEG_ZERO, POS_ONE, NEG_ONE, POS_EVENS, NEG_EVENS])
.iter()
.for_each(|int_set| {
int_set.iter().for_each(|int| {
Expand All @@ -616,7 +616,7 @@ mod tests {

// Negative base (imaginary results):
// (-anything except 0 and Infinity ^ non-integer should be NAN)
&NEG[1..(NEG.len() - 1)].iter().for_each(|set| {
(&NEG[1..(NEG.len() - 1)]).iter().for_each(|set| {
set.iter().for_each(|val| {
test_sets(&ALL[3..7], &|v: f64| pow(*val, v), &|_| NAN);
})
Expand Down