Make contraction label derivation type-stable#192
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Derives the bipartitioned permutations for `contract` as concretely-typed tuples behind a single `Val` function-barrier on the contracted count, rather than building them by converting runtime-length `Vector`s into abstract-typed tuples. The abstract tuples defeated the type stability of the downstream `matricize` pipeline, which is built around statically-sized tuples and `Val` barriers, so the per-call bookkeeping for a small contraction boxed heavily. This is a second pass on the label-derivation layer, after #190 removed the `Set` and `Dict` hashing from the same path. For a 4x4 matrix multiply the per-call cost drops from 51 allocations to 17 and is several times faster, landing just above the floor set by the lower-level entry point that takes the permutations directly. The remaining allocations are the output array temporaries and the destination-label `Vector`. The public `biperms` and `biperm` signatures are unchanged. The type-stable core is a new `Val`-parameterized method of `biperms`, and the two label entry points cross into `Val`-specialized helpers so the contraction itself runs type-stably.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #192 +/- ##
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+ Coverage 82.46% 82.69% +0.23%
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Files 22 22
Lines 616 630 +14
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+ Hits 508 521 +13
- Misses 108 109 +1
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Summary
Derives the bipartitioned permutations for
contractas concretely-typed tuples behind a singleValfunction-barrier on the contracted count, rather than building them by converting runtime-lengthVectors into abstract-typed tuples. The abstract tuples defeated the type stability of the downstreammatricizepipeline, which is built around statically-sized tuples andValbarriers, so the per-call bookkeeping for a small contraction boxed heavily.This is a second pass on the label-derivation layer, after #190 removed the
SetandDicthashing from the same path. For a 4x4 matrix multiply the per-call cost drops from 51 allocations to 17 and is several times faster, landing just above the floor set by the lower-level entry point that takes the permutations directly. The remaining allocations are the output array temporaries and the destination-labelVector.The public
bipermsandbipermsignatures are unchanged. The type-stable core is a newVal-parameterized method ofbiperms, and the two label entry points cross intoVal-specialized helpers so the contraction itself runs type-stably.