27 lines
1.1 KiB
Rust
27 lines
1.1 KiB
Rust
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//! Helper functions for sparse matrix computations
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/// permutes entries of in_slice according to permutation slice and puts them to out_slice
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#[inline]
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pub fn apply_permutation<T: Clone>(out_slice: &mut [T], in_slice: &[T], permutation: &[usize]) {
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assert_eq!(out_slice.len(), in_slice.len());
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assert_eq!(out_slice.len(), permutation.len());
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for (out_element, old_pos) in out_slice.iter_mut().zip(permutation) {
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*out_element = in_slice[*old_pos].clone();
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}
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}
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/// computes permutation by using provided indices as keys
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#[inline]
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pub fn compute_sort_permutation(permutation: &mut [usize], indices: &[usize]) {
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assert_eq!(permutation.len(), indices.len());
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// Set permutation to identity
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for (i, p) in permutation.iter_mut().enumerate() {
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*p = i;
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}
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// Compute permutation needed to bring minor indices into sorted order
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// Note: Using sort_unstable here avoids internal allocations, which is crucial since
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// each lane might have a small number of elements
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permutation.sort_unstable_by_key(|idx| indices[*idx]);
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}
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