add value and type constructors for variable-length buffers and sha256 ctx8#372
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apoelstra wants to merge 5 commits into
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add value and type constructors for variable-length buffers and sha256 ctx8#372apoelstra wants to merge 5 commits into
apoelstra wants to merge 5 commits into
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The core::array::from_fn has been stable since Rust 1.63. We can use this to build an array, rather than constructing a vector, converting it to an arary, and unwrapping the conversion. This saves an allocation, eliminates a panic path, and (IMHO) makes the code easier to read. I need to duplicate this logic for the buffer type in the next commit, so I figured I should first clean it up.
This function panics if given an n which is out of range. This is arguably fine but we might as well return a Result, which gives the user the choice of whether or not to panic. Because the overwhelming number of calls in this codebase provide a fixed compile-time constant, also add a Final::two_two_n_fixed method which takes a complie-time constant and fails to compile if it's out of range.
Add precomputation tables for both `Tmr` and `Final`. Write a unit test which does a direct computation of the type and verifies all the precomp vectors. Also check against the Ctx8 output type of the sha256 init jet. Don't provide a Final::buffer8_two_n_plus_one_fixed function that avoids the Result by doing a compile-time check. It seems unlikely that this will be called with compile-time fixed values, except for the value 5 which is used in the Ctx8 type. But in the next commit we'll special-case Ctx8.
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This PR lays the groundwork for constructing and manipulating SHA256 contexts in an ergonomic way. This lets you construct variable-length buffers, and by producting those with a couple fixed-size words you can create a context. It also provides precomputed types for various sizes of buffers and
Ctx8itself.A later PR will implement conversions between these objects and Rust
sha256::Engineobjects, but this may require an update to bitcoin-hashes 1.0 so I am still working out how to do that.