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//! Constant-scratch sorting for embedded routing identifiers.
//!
//! The standard numeric small-sort specializations trade flash for speed.
//! Route/recipient lists do not need those unrolled sorting networks. Heapsort
//! retains O(n log n) worst-case work, no recursion, and no heap allocation.
pub(crate) fn sort<T: Ord>(values: &mut [T]) {
#[cfg(not(feature = "embedded"))]
values.sort_unstable();
#[cfg(feature = "embedded")]
heap_sort(values);
}
#[cfg(any(feature = "embedded", test))]
fn heap_sort<T: Ord>(values: &mut [T]) {
fn sift<T: Ord>(values: &mut [T], mut root: usize, end: usize) {
while root < end / 2 {
let mut child = root * 2 + 1;
if child + 1 < end && values[child] < values[child + 1] {
child += 1;
}
if values[root] >= values[child] {
break;
}
values.swap(root, child);
root = child;
}
}
let len = values.len();
for root in (0..len / 2).rev() {
sift(values, root, len);
}
for end in (1..len).rev() {
values.swap(0, end);
sift(values, 0, end);
}
}
#[cfg(test)]
mod tests {
use super::heap_sort;
#[test]
fn embedded_sort_matches_standard_for_routing_lists() {
for length in [0, 1, 2, 3, 7, 8, 13, 16, 31, 32, 255, 256, 1024] {
for pattern in 0..5 {
let mut seed = 0x123456789abcdefu64;
let mut values: alloc::vec::Vec<u64> = (0..length)
.map(|i| {
seed ^= seed << 13;
seed ^= seed >> 7;
seed ^= seed << 17;
match pattern {
0 => i as u64,
1 => (length - i) as u64,
2 => seed % 7,
3 => {
if i % 2 == 0 {
u64::MAX
} else {
0
}
}
_ => seed,
}
})
.collect();
let mut expected = values.clone();
expected.sort_unstable();
heap_sort(&mut values);
assert_eq!(values, expected, "length={length}, pattern={pattern}");
}
}
}
}