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fix: Remove branching on carry propagation for Montgomery reduction - #166
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hubot merged 1 commit intoOct 6, 2026
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…endent branch - replace the `while carry != 0` tail in the five hand-written scalar REDCs and the shared montgomery::redc with a `for` over the limbs above the addition window, so the trip count depends only on the public round index, never on the (secret-derived) operands - behaviour is unchanged: once the carry has propagated out, the remaining iterations add 0; CAVP SigGen, wycheproof (all curves) and RFC 6979 suites pin identical signature bytes (760 tests pass) - release asm for all eleven redc/finish_redc functions now contains zero data-dependent conditional jumps (previously 22), making the branch-free contracts in ec/src/lib.rs and ecdsa/src/lib.rs accurate - diff-scoped cargo mutants (ec plus ecdsa test packages): 34/34 caught - rewrite the stale "genuinely reachable branch" and "accepted equivalent mutant" comments that described the old while loops Assisted-by: Claude:claude-fable-5
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Make REDC carry propagation a counted loop, removing a secret-dependent branching
while carry != 0tail in the five hand-written scalar REDCs and the shared montgomery::redc with aforover the limbs above the addition window, so the trip count depends only on the public round index, never on the (secret-derived) operandsAssisted-by: Claude:claude-fable-5