kaidokert / modmath-rs / 28921817015

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Carry detection via ct_lt across the CT wide-REDC path (#29)

overflowing_add's carry flag has no branchless materialization on ISAs
without a flags register: LLVM lowers the 64-bit carry-out as an
equality-branch chain on operand-derived values on riscv32 — the
findings ct-driver documented in RISCV32_EXTRA_HELPERS. The wraparound
test sum.ct_lt(&a) (already the idiom in safegcd's se_add and
Field::add) is pure mask arithmetic on every target and carries as
subtle::Choice end to end, so the Choice::from(bool) laundering at the
finalize sites disappears too.

74 of 74 new or added lines in 2 files covered. (100.0%)

6181 of 6288 relevant lines covered (98.3%)

15415.44 hits per line