Fix correctness bugs and bump to v0.4.1#34
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gvonness-apolitical merged 2 commits intomainfrom Mar 14, 2026
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…and codebase review fixes (v0.4.1) Fix three deferred correctness bugs from the codebase review plus pre-existing fixes from the review session: - powi on f32 bytecode tapes silently produced wrong values/gradients for negative exponents due to precision loss in the u32→f32→u32 round-trip. All 5 dispatch sites now decode directly from raw u32. - Taylor::powi produced NaN for negative base values (e.g. (-2)^3) because it used exp(n*ln(a)). Added binary exponentiation path for negative base or small exponents. - Checkpoint position lookups converted from Vec::contains (O(n)) to HashSet (O(1)) in all three checkpointing variants. - Pre-existing review fixes: Rem derivative corrections for Dual/Reverse/ BReverse, hypot zero-division guard, powi overflow guard, Round kink detection at half-integers, CSE custom-op handling, optimize() dedup, grad() constant-output fast path, sparsity Powi/Custom handling. Bump version to 0.4.1. Update CHANGELOG and SECURITY.
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Summary
Fixes three deferred correctness bugs from the codebase review (all produced silently wrong results) plus pre-existing review fixes:
powi(n)on f32 tapes silently returned wrong values/gradients for negative exponents (n <= -2) due to precision loss in theu32 → f32 → u32round-trip. All 5 dispatch sites (forward, reverse, tangent fwd/rev, cross-country) now decode the exponent directly from rawu32viapowi_exp_decode_raw.Taylor::powiproduced NaN for negative base (e.g.(-2)^3) because it usedexp(n * ln(a)). Addedtaylor_powi_squaringusing binary exponentiation for negative base or|n| <= 8.grad_checkpointed,grad_checkpointed_disk,grad_checkpointed_with_hintsusedVec::contains()(O(n) per step). Converted toHashSetfor O(1).Bumps version to 0.4.1 with updated CHANGELOG and SECURITY.
Test plan
cargo test --features bytecode,taylor,stde,parallel,diffop,laurent— all 600+ tests passcargo clippy --features bytecode,taylor,stde,parallel,diffop,laurent -- -D warnings— cleanpowi(-2)andpowi(-10)value+gradient,powi_exp_decode_rawround-trip, Taylor powi with negative base (squared, cubed, 4th power, negative exponent), positive base regression