cmov: use masksel to impl CmovEq
#1343
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Uses the `masksel` function added in #1342 to impl `CmovEq`. This should be less circuitious than the previous implementation. This approach means we can get rid of all of the `test*` functions like `testeq*`, `testne*`, and `testnz*` and implement everything in terms of mask generation. The pure Rust versions of `masknz32` and `masknz64` still internally use `black_box` to prevent optimizations around the non-zero bit extracted before computing the mask.
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Uses the
maskselfunction added in #1342 to implCmovEq. This should be less circuitious than the previous implementation.This approach means we can get rid of all of the
test*functions liketesteq*,testne*, andtestnz*and implement everything in terms of mask generation.The pure Rust versions of
masknz32andmasknz64still internally useblack_boxto prevent optimizations around the non-zero bit extracted before computing the mask.