ctutils: split CtAssign out of CtSelect [BREAKING]#1363
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Note: version bumped to v0.4.0-pre to denote breaking change (not for release) Extracts the `ct_assign` method into its own trait. The main advantage of this is the `CtSelect` trait requires a `Sized` bound, where an independent `CtAssign` trait does not, which means it can be impl'd for slices as a sort of conditional `copy_from_slice`. The main disadvantage is we lose the default implementation, so it becomes one more trait to impl. There's no good way to blanket impl one in terms of the other that won't preclude efficient implementations in some way or another, so this opts not to do that for maximum flexibility. To preserve `subtle`-like ergonomics where `CtSelect` means we can `CtAssign` as well, this bounds `CtSelect` on `CtAssign`. Finally, the same treatment is given to the `Bytes*` traits, with a `BytesCtAssign` split out of `BytesCtSelect` for parity, and an impl of `BytesCtAssign` for `[u8]` has been added.
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tarcieri
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Jan 20, 2026
## Added - `core::num::NonZero<T>` support (#1368) - Pluggable trait impls for `[T]` and `[T; N]` with helper traits: (#1388) - `CtAssign`: `CtAssignSlice` - `CtEq`: `CtEqSlice` - `CtSelect`: `CtSelectArray` - `CtSelectUsingCtAssign` marker trait (#1391) ## Changed - Split `CtAssign` out of `CtSelect` (#1363) - Bump `cmov` to v0.5 (#1386) ## Removed - `BytesCtEq`/`BytesCtSelect` no longer needed because default `[u8]` impls are fast (#1376) - `target_pointer_width` gating (#1389) - `unsafe` code (#1405)
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Note: version bumped to v0.4.0-pre to denote breaking change (not for release)
Extracts the
ct_assignmethod into its own trait. The main advantage of this is theCtSelecttrait requires aSizedbound, where an independentCtAssigntrait does not, which means it can be impl'd for slices as a sort of conditionalcopy_from_slice.The main disadvantage is we lose the default implementation, so it becomes one more trait to impl. There's no good way to blanket impl one in terms of the other that won't preclude efficient implementations in some way or another, so this opts not to do that for maximum flexibility.
To preserve
subtle-like ergonomics whereCtSelectmeans we canCtAssignas well, this boundsCtSelectonCtAssign.Finally, the same treatment is given to the
Bytes*traits, with aBytesCtAssignsplit out ofBytesCtSelectfor parity, and an impl ofBytesCtAssignfor[u8]has been added.