Add IsSorted to hwy/contrib/algo#3111
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Vectorized equivalent of std::is_sorted, with an overload taking a comparator func (per google#3094): the range is sorted iff comp(d, in[i+1], in[i]) is false for all i. The default overload checks non-decreasing order via Lt. Based on the loop structure of find-inl.h: 2x-unrolled overlapping offset-by-one loads, AllFalse early-exit, masked LoadN tail.
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Fix for the pre-existing CI breakage is up: #3113. Happy to rebase this PR once it lands. |
jan-wassenberg
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Jun 12, 2026
jan-wassenberg
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Very nice, thanks for adding - and impressive speedups :) We'll probably be able to merge already because internal tests are green.
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Adds
IsSortedtohwy/contrib/algo, from the op wishlist. Closes #3094.IsSorted(d, in, count)matchesstd::is_sorted(non-decreasing). Per #3094 there is also a comparator overload:comp(d, a, b)returns a mask, true whereais ordered strictly beforeb— e.g. passingGtchecks descending order. The default forwardsLt.Implementation follows
find-inl.h: 2x-unrolled loop comparing each vector with an overlapping load offset by one element,AllFalse(Or(...))early-exit, maskedLoadNtail.Tests check both overloads against scalar references: random and boundary lengths, 3 misalignments, random / sorted / all-equal / single-descent inputs (including descents at block boundaries and the last pair). Pass locally on NEON, NEON_BF16, NEON_WITHOUT_AES, EMU128.
Performance vs
std::is_sorted(Apple M4 Pro, clang 21-O2, 64Ki sorted elements = full scan; scalar baseline ~15 µs):