revm-precompile 29.0.1

Revm Precompiles - Ethereum compatible precompiled contracts
Documentation 
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//! Utility function that precompiles use, padding and converting between types.
use primitives::{b256, Bytes, B256};
use std::borrow::Cow;

/// Right-pads the given slice at `offset` with zeroes until `LEN`.
///
/// Returns the first `LEN` bytes if it does not need padding.
#[inline]
pub fn right_pad_with_offset<const LEN: usize>(data: &[u8], offset: usize) -> Cow<'_, [u8; LEN]> {
    right_pad(data.get(offset..).unwrap_or_default())
}

/// Right-pads the given slice at `offset` with zeroes until `len`.
///
/// Returns the first `len` bytes if it does not need padding.
#[inline]
pub fn right_pad_with_offset_vec(data: &[u8], offset: usize, len: usize) -> Cow<'_, [u8]> {
    right_pad_vec(data.get(offset..).unwrap_or_default(), len)
}

/// Right-pads the given slice with zeroes until `LEN`.
///
/// Returns the first `LEN` bytes if it does not need padding.
#[inline]
pub fn right_pad<const LEN: usize>(data: &[u8]) -> Cow<'_, [u8; LEN]> {
    if let Some(data) = data.get(..LEN) {
        Cow::Borrowed(data.try_into().unwrap())
    } else {
        let mut padded = [0; LEN];
        padded[..data.len()].copy_from_slice(data);
        Cow::Owned(padded)
    }
}

/// Right-pads the given slice with zeroes until `len`.
///
/// Returns the first `len` bytes if it does not need padding.
#[inline]
pub fn right_pad_vec(data: &[u8], len: usize) -> Cow<'_, [u8]> {
    if let Some(data) = data.get(..len) {
        Cow::Borrowed(data)
    } else {
        let mut padded = vec![0; len];
        padded[..data.len()].copy_from_slice(data);
        Cow::Owned(padded)
    }
}

/// Left-pads the given slice with zeroes until `LEN`.
///
/// Returns the first `LEN` bytes if it does not need padding.
#[inline]
pub fn left_pad<const LEN: usize>(data: &[u8]) -> Cow<'_, [u8; LEN]> {
    if let Some(data) = data.get(..LEN) {
        Cow::Borrowed(data.try_into().unwrap())
    } else {
        let mut padded = [0; LEN];
        padded[LEN - data.len()..].copy_from_slice(data);
        Cow::Owned(padded)
    }
}

/// Left-pads the given slice with zeroes until `len`.
///
/// Returns the first `len` bytes if it does not need padding.
#[inline]
pub fn left_pad_vec(data: &[u8], len: usize) -> Cow<'_, [u8]> {
    if let Some(data) = data.get(..len) {
        Cow::Borrowed(data)
    } else {
        let mut padded = vec![0; len];
        padded[len - data.len()..].copy_from_slice(data);
        Cow::Owned(padded)
    }
}

/// Converts a boolean to a left-padded 32-byte [`Bytes`] value.
///
/// This is optimized to not allocate at runtime by using 2 static arrays.
#[inline]
pub const fn bool_to_bytes32(value: bool) -> Bytes {
    Bytes::from_static(&bool_to_b256(value).0)
}

/// Converts a boolean to a left-padded [`B256`] value.
///
/// This is optimized to not allocate at runtime by using 2 static arrays.
#[inline]
pub const fn bool_to_b256(value: bool) -> &'static B256 {
    const TRUE: &B256 =
        &b256!("0x0000000000000000000000000000000000000000000000000000000000000001");
    const FALSE: &B256 =
        &b256!("0x0000000000000000000000000000000000000000000000000000000000000000");
    if value {
        TRUE
    } else {
        FALSE
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn get_with_right_padding() {
        let data = [1, 2, 3, 4];
        let padded = right_pad_with_offset::<8>(&data, 4);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [0, 0, 0, 0, 0, 0, 0, 0]);
        let padded = right_pad_with_offset_vec(&data, 4, 8);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [0, 0, 0, 0, 0, 0, 0, 0]);

        let data = [1, 2, 3, 4, 5, 6, 7, 8];
        let padded = right_pad_with_offset::<8>(&data, 0);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);
        let padded = right_pad_with_offset_vec(&data, 0, 8);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);

        let data = [1, 2, 3, 4, 5, 6, 7, 8];
        let padded = right_pad_with_offset::<8>(&data, 4);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [5, 6, 7, 8, 0, 0, 0, 0]);
        let padded = right_pad_with_offset_vec(&data, 4, 8);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [5, 6, 7, 8, 0, 0, 0, 0]);
    }

    #[test]
    fn right_padding() {
        let data = [1, 2, 3, 4];
        let padded = right_pad::<8>(&data);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 0, 0, 0, 0]);
        let padded = right_pad_vec(&data, 8);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 0, 0, 0, 0]);

        let data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
        let padded = right_pad::<8>(&data);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);
        let padded = right_pad_vec(&data, 8);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);
    }

    #[test]
    fn left_padding() {
        let data = [1, 2, 3, 4];
        let padded = left_pad::<8>(&data);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [0, 0, 0, 0, 1, 2, 3, 4]);
        let padded = left_pad_vec(&data, 8);
        assert!(matches!(padded, Cow::Owned(_)));
        assert_eq!(padded[..], [0, 0, 0, 0, 1, 2, 3, 4]);

        let data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
        let padded = left_pad::<8>(&data);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);
        let padded = left_pad_vec(&data, 8);
        assert!(matches!(padded, Cow::Borrowed(_)));
        assert_eq!(padded[..], [1, 2, 3, 4, 5, 6, 7, 8]);
    }

    #[test]
    fn bool2bytes() {
        let f = bool_to_bytes32(false);
        assert_eq!(f[..], [0; 32]);
        let t = bool_to_bytes32(true);
        assert_eq!(t.len(), 32);
        assert_eq!(t[..31], [0; 31]);
        assert_eq!(t[31], 1);
    }
}