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pow matrix: remove unnecessary conditions in Matrix::compute_rank #517

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pow matrix: remove unnecessary conditions in Matrix::compute_rank #517

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2f2b8a6
consensus: slightly optimize Matrix::compute_rank
Slixe Aug 14, 2024
6c72d81
matrix: remove unsafe usage for convert_to_float
Slixe Aug 14, 2024
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40 changes: 17 additions & 23 deletions consensus/pow/src/matrix.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,16 +51,15 @@ impl Matrix {

#[inline(always)]
fn convert_to_float(&self) -> [[f64; 64]; 64] {
// SAFETY: An uninitialized MaybeUninit is always safe.
let mut out: [[MaybeUninit<f64>; 64]; 64] = unsafe { MaybeUninit::uninit().assume_init() };
let mut out: [[f64; 64]; 64] = [[Default::default(); 64]; 64];

out.iter_mut().zip(self.0.iter()).for_each(|(out_row, mat_row)| {
out_row.iter_mut().zip(mat_row).for_each(|(out_element, &element)| {
out_element.write(f64::from(element));
*out_element = f64::from(element);
})
});
// SAFETY: The loop above wrote into all indexes.
unsafe { std::mem::transmute(out) }

out
Comment on lines -54 to +62
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This will be much slower, this one seems to optimize as well as the original:
std::array::from_fn(|i| std::array::from_fn(|j| f64::from(self.0[i][j])))

See profiling(llvm-mca) and assembly here: https://godbolt.org/z/q5aj7chn6

}

pub fn compute_rank(&self) -> usize {
Expand All @@ -69,30 +68,25 @@ impl Matrix {
let mut rank = 0;
let mut row_selected = [false; 64];
for i in 0..64 {
if i >= 64 {
// Required for optimization, See https://github.com/rust-lang/rust/issues/90794
unreachable!()
}
Comment on lines -72 to -75
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It seems like this issue was resolved:
rust-lang/rust#90794, But I just checked in godbolt and it does reduces optimizations

let mut j = 0;
while j < 64 {
if !row_selected[j] && mat_float[j][i].abs() > EPS {
break;
}
j += 1;
}
if j != 64 {
rank += 1;
row_selected[j] = true;
for p in (i + 1)..64 {
mat_float[j][p] /= mat_float[j][i];
}
for k in 0..64 {
if k != j && mat_float[k][i].abs() > EPS {
for p in (i + 1)..64 {
mat_float[k][p] -= mat_float[j][p] * mat_float[k][i];
rank += 1;
row_selected[j] = true;
for p in (i + 1)..64 {
mat_float[j][p] /= mat_float[j][i];
}
for k in 0..64 {
if k != j && mat_float[k][i].abs() > EPS {
for p in (i + 1)..64 {
mat_float[k][p] -= mat_float[j][p] * mat_float[k][i];
}
}
}

break;
}
j += 1;
}
}
rank
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