Merge pull request #270 from DaniPopes/byte-fn

feat: add `Uint::byte`

CHANGELOG.md

@@ -9,17 +9,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Introduce `ark-ff-04` feature flag for conversion to `[email protected]` types.
+### Added
+
+- Introduce `ark-ff-04` feature flag for conversion to `[email protected]` types
 - Support for [`alloy-rlp`](https://github.com/alloy-rs/rlp)
-- MSRV (Minimum Supported Rust Version) is now set at 1.65.0, from previously undefined.
+- MSRV (Minimum Supported Rust Version) is now set at 1.65.0, from previously undefined
 - Implement `TryFrom<bool>` for `Uint`
+- New method: `byte`
 
 ### Changed
 
 - Make `serde::Deserialize` impl more permissive
 - Use Ethereum `Quantity` encoding for serde serialization when human-readable
-- Fix error in `from_base_be` that allowed instantiation of overflowing `Uint`.
-- Updated `fastrlp` to `0.3`, `pyo3` to `0.19`, and `sqlx-core` to `0.7`.
+- Fix error in `from_base_be` that allowed instantiation of overflowing `Uint`
+- Updated `fastrlp` to `0.3`, `pyo3` to `0.19`, and `sqlx-core` to `0.7`
 - Improved `fastrlp` perfomance
 - Improved `proptest` performance
 - Made `support` module and its modules public
@@ -28,7 +31,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Removed
 
-- Automatic detection of nightly features. Enable them instead with the `nightly` cargo feature.
+- Automatic detection of nightly features. Enable them instead with the `nightly` cargo feature
 - Dependency on `derive_more`
 
 ### Fixed

src/bits.rs

@@ -5,7 +5,11 @@ use core::ops::{
 };
 
 impl<const BITS: usize, const LIMBS: usize> Uint<BITS, LIMBS> {
+    /// Returns whether a specific bit is set.
+    ///
+    /// Returns `false` if `index` exceeds the bit width of the number.
     #[must_use]
+    #[inline]
     pub const fn bit(&self, index: usize) -> bool {
         if index >= BITS {
             return false;
@@ -14,6 +18,8 @@ impl<const BITS: usize, const LIMBS: usize> Uint<BITS, LIMBS> {
         self.limbs[limbs] & (1 << bits) != 0
     }
 
+    /// Sets a specific bit to a value.
+    #[inline]
     pub fn set_bit(&mut self, index: usize, value: bool) {
         if index >= BITS {
             return;
@@ -26,6 +32,46 @@ impl<const BITS: usize, const LIMBS: usize> Uint<BITS, LIMBS> {
         }
     }
 
+    /// Returns a specific byte. The byte at index `0` is the least significant
+    /// byte (little endian).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` exceeds the byte width of the number.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use ruint::uint;
+    /// let x = uint!(0x1234567890_U64);
+    /// let bytes = [
+    ///     x.byte(0), // 0x90
+    ///     x.byte(1), // 0x78
+    ///     x.byte(2), // 0x56
+    ///     x.byte(3), // 0x34
+    ///     x.byte(4), // 0x12
+    ///     x.byte(5), // 0x00
+    ///     x.byte(6), // 0x00
+    ///     x.byte(7), // 0x00
+    /// ];
+    /// assert_eq!(bytes, x.to_le_bytes());
+    /// ```
+    ///
+    /// Panics if out of range.
+    ///
+    /// ```should_panic
+    /// # use ruint::uint;
+    /// let x = uint!(0x1234567890_U64);
+    /// let _ = x.byte(8);
+    /// ```
+    #[inline]
+    #[must_use]
+    #[track_caller]
+    #[allow(clippy::cast_possible_truncation)] // intentional
+    pub const fn byte(&self, index: usize) -> u8 {
+        (self.limbs[index / 8] >> ((index % 8) * 8)) as u8
+    }
+
     /// Reverses the order of bits in the integer. The least significant bit
     /// becomes the most significant bit, second least-significant bit becomes
     /// second most-significant bit, etc.
@@ -660,8 +706,7 @@ mod tests {
     }
 
     #[test]
-    #[allow(clippy::cast_lossless)]
-    #[allow(clippy::cast_possible_truncation)]
+    #[allow(clippy::cast_lossless, clippy::cast_possible_truncation)]
     fn test_small() {
         const_for!(BITS in [1, 2, 8, 16, 32, 63, 64] {
             type U = Uint::<BITS, 1>;