ctutils: CtOption methods for crypto-bigint
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Analogous to what #1035 did for `ConstChoice`, this extracts the necessary methods onto `ctutils::CtOption` then replaces the type wholesale using the implementation in `ctutils`. There were a few tricky parts, namely we had type-specific implementations of `expect` and `unwrap_or`. It is actually possible to write a generic `const fn` implementation of `CtOption::expect`, avoiding the problems with destructors and the unstable `Destruct` trait, by bounding on `T: Copy` and returning a copy of the inner value. This is implemented as `CtOption::expect_copied` so we can still support `expect` for non-`Copy` types. Unfortunately there's no analogous generic `const fn` solution for `CtOption::unwrap_or`, as this needs a constant-time selector function and even function pointers can't be used from a `const fn`. So this does the only thing we can do to replace it with some level of abstraction: a `ctutils::unwrap_or!` macro. See also: RustCrypto/utils#1274 which extracts some needed methods onto `ctutils::CtOption`.
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Analogous to what #1035 did for `ConstChoice`, this extracts the necessary methods onto `ctutils::CtOption` then replaces the type wholesale using the implementation in `ctutils`. There were a few tricky parts, namely we had type-specific implementations of `expect` and `unwrap_or`. It is actually possible to write a generic `const fn` implementation of `CtOption::expect`, avoiding the problems with destructors and the unstable `Destruct` trait, by bounding on `T: Copy` and returning a copy of the inner value. This is implemented as `CtOption::expect_copied` so we can still support `expect` for non-`Copy` types. Unfortunately there's no analogous generic `const fn` solution for `CtOption::unwrap_or`, as this needs a constant-time selector function and even function pointers can't be used from a `const fn`. So this does the only thing we can do to replace it with some level of abstraction: a `ctutils::unwrap_or!` macro. See also: RustCrypto/utils#1274 which extracts some needed methods onto `ctutils::CtOption`.
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Analogous to what #1035 did for `ConstChoice`, this extracts the necessary methods onto `ctutils::CtOption` then replaces the type wholesale using the implementation in `ctutils`. There were a few tricky parts, namely we had type-specific implementations of `expect` and `unwrap_or`. It is actually possible to write a generic `const fn` implementation of `CtOption::expect`, avoiding the problems with destructors and the unstable `Destruct` trait, by bounding on `T: Copy` and returning a copy of the inner value. This is implemented as `CtOption::expect_copied` so we can still support `expect` for non-`Copy` types. Unfortunately there's no analogous generic `const fn` solution for `CtOption::unwrap_or`, as this needs a constant-time selector function and even function pointers can't be used from a `const fn`. So this does the only thing we can do to replace it with some level of abstraction: a `ctutils::unwrap_or!` macro. See also: RustCrypto/utils#1274 which extracts some needed methods onto `ctutils::CtOption`.
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CtOption methods for crypto-bigintCtOption methods for crypto-bigint
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Adds the methods needed to replace `ConstCtOption` in `crypto-bigint` with `ctutils::CtOption`: - `some` - `none` - `into_option_copied` - `and_choice` - `as_inner_unchecked` - `to_inner_unchecked` Also adds a `Default` impl for `CtOption`. Also adds `map!` and `unwrap_or!` macros to provide `const fn`-friendly combinator-like functionality.
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tarcieri
added a commit
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Dec 27, 2025
Analogous to what #1035 did for `ConstChoice`, this extracts the necessary methods onto `ctutils::CtOption` then replaces the type wholesale using the implementation in `ctutils`. There were a few tricky parts, namely we had type-specific implementations of `expect` and `unwrap_or`. It is actually possible to write a generic `const fn` implementation of `CtOption::expect`, avoiding the problems with destructors and the unstable `Destruct` trait, by bounding on `T: Copy` and returning a copy of the inner value. This is implemented as `CtOption::expect_copied` so we can still support `expect` for non-`Copy` types. Unfortunately there's no analogous generic `const fn` solution for `CtOption::unwrap_or`, as this needs a constant-time selector function and even function pointers can't be used from a `const fn`. So this does the only thing we can do to replace it with some level of abstraction: a `ctutils::unwrap_or!` macro. See also: RustCrypto/utils#1274 which extracts some needed methods onto `ctutils::CtOption`.
tarcieri
added a commit
to RustCrypto/crypto-bigint
that referenced
this pull request
Dec 27, 2025
Analogous to what #1035 did for `ConstChoice`, this extracts the necessary methods onto `ctutils::CtOption` then replaces the type wholesale using the implementation in `ctutils`. There were a few tricky parts, namely we had type-specific implementations of `expect` and `unwrap_or`. It is actually possible to write a generic `const fn` implementation of `CtOption::expect`, avoiding the problems with destructors and the unstable `Destruct` trait, by bounding on `T: Copy` and returning a copy of the inner value. This is implemented as `CtOption::expect_copied` so we can still support `expect` for non-`Copy` types. Unfortunately there's no analogous generic `const fn` solution for `CtOption::unwrap_or`, as this needs a constant-time selector function and even function pointers can't be used from a `const fn`. So this does the only thing we can do to replace it with some level of abstraction: a `ctutils::unwrap_or!` macro. See also: RustCrypto/utils#1274 which extracts some needed methods onto `ctutils::CtOption`.
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Adds the methods needed to replace
ConstCtOptionincrypto-bigintwithctutils::CtOption:somenoneinto_option_copiedand_choiceas_inner_uncheckedto_inner_uncheckedAlso adds a
Defaultimpl forCtOption.Also adds
map!andunwrap_or!macros to provideconst fn-friendly combinator-like functionality.