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ctutils: constant-time hardening for non-zero comparisons - #1582
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Extends `cargo checkct` coverage to cover non-zero comparisons via `Choice`, uncovering some non-constant-time code generation on `riscv32` and Thumb-1 targets. Addresses the problem with a new `nonzero_primitive!` macro and selective use of `black_box` on these targets, using `cargo checkct` to verify this addresses the issue. This should not have an impact on codegen on other platforms, which were already constant-time.
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This includes unreleased fixes from RustCrypto/utils#1582 as well as some Thumb-1 specific fixes
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Extends
cargo checkctcoverage to cover non-zero comparisons viaChoice, uncovering some non-constant-time code generation onriscv32and Thumb-1 targets.Addresses the problem with a new
nonzero_primitive!macro and selective use ofblack_boxon these targets, usingcargo checkctto verify this addresses the issue. This should not have an impact on codegen on other platforms, which were already constant-time.