80fdfb2376
* Generate debug symbols in optimized builds. This allows profiling tools to provide more accurate information, especially details about inlined functions. * Rewrite and optimize partition_slice This improves the performance of the register allocation passes which use LiveValueTracker.
98 lines
2.6 KiB
Rust
98 lines
2.6 KiB
Rust
//! Rearrange the elements in a slice according to a predicate.
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use std::mem;
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/// Rearrange the elements of the mutable slice `s` such that elements where `p(t)` is true precede
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/// the elements where `p(t)` is false.
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///
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/// The order of elements is not preserved, unless the slice is already partitioned.
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///
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/// Returns the number of elements where `p(t)` is true.
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pub fn partition_slice<T, F>(s: &mut [T], mut p: F) -> usize
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where
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F: FnMut(&T) -> bool,
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{
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// The iterator works like a deque which we can pop from both ends.
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let mut i = s.iter_mut();
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// Number of elements for which the predicate is known to be true.
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let mut pos = 0;
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loop {
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// Find the first element for which the predicate fails.
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let head = loop {
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match i.next() {
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Some(head) => {
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if !p(&head) {
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break head;
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}
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}
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None => return pos,
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}
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pos += 1;
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};
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// Find the last element for which the predicate succeeds.
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let tail = loop {
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match i.next_back() {
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Some(tail) => {
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if p(&tail) {
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break tail;
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}
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}
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None => return pos,
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}
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};
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// Swap the two elements into the right order.
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mem::swap(head, tail);
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pos += 1;
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}
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}
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#[cfg(test)]
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mod tests {
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use super::partition_slice;
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use std::vec::Vec;
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fn check(x: &[u32], want: &[u32]) {
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assert_eq!(x.len(), want.len());
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let want_count = want.iter().cloned().filter(|&x| x % 10 == 0).count();
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let mut v = Vec::new();
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v.extend(x.iter().cloned());
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let count = partition_slice(&mut v[..], |&x| x % 10 == 0);
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assert_eq!(v, want);
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assert_eq!(count, want_count);
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}
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#[test]
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fn empty() {
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check(&[], &[]);
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}
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#[test]
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fn singles() {
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check(&[0], &[0]);
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check(&[1], &[1]);
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check(&[10], &[10]);
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}
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#[test]
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fn doubles() {
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check(&[0, 0], &[0, 0]);
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check(&[0, 5], &[0, 5]);
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check(&[5, 0], &[0, 5]);
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check(&[5, 4], &[5, 4]);
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}
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#[test]
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fn longer() {
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check(&[1, 2, 3], &[1, 2, 3]);
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check(&[1, 2, 10], &[10, 2, 1]); // Note: 2, 1 order not required.
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check(&[1, 10, 2], &[10, 1, 2]); // Note: 1, 2 order not required.
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check(&[1, 20, 10], &[10, 20, 1]); // Note: 10, 20 order not required.
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check(&[1, 20, 3, 10], &[10, 20, 3, 1]);
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check(&[20, 3, 10, 1], &[20, 10, 3, 1]);
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}
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}
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