reduce boilerplate implementing comparisons for user-defined types #99
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This was referenced Dec 31, 2022
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- fix compiler warnings about unused #[inline]
- spelling fix
- rustfmt change
- remove trait bounds on the ConstantTimeLess trait declaration itself
- implement ConstantTime{Less,Greater} with shortlex too
- improve comments on ct_gt impl
- remove extraneous mentions of shortlex
- iterated operations
- revert ConstantTimeLess back to using the default trait method
- remove `.unwrap_u8()`: does this break `ConstantTimeEq` slice impl?
- remove unused code
- implement ConstantTimeLess for slices
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Problem
In signalapp/libsignal#469, we discussed having to hand-roll a constant-time comparison function for a public key with a slice of bytes and an enum tag. After seeing #78 where we implement
ConstantTimeEqfor slices, I realized we could extend this method of iterated constant-time computation to make it more fluent to implement comparison operations for structs with multiple fields.Proposed Solution
IteratedOperationandIteratedEqto modularize the approach used in the existingConstantTimeEqimpl for slices.ConstantTimeGreaterover a collection of elements asLexicographicIteratedGreater.ConstantTimeGreaterfor slices usingLexicographicIteratedGreater.Result
ConstantTimeOrdwill be implemented automatically for slices if/when define and implementConstantTime{Partial,}Ordtraits #98 is merged.