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perf(primitives): improve checksum algorithm #713

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Aug 25, 2024
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perf(primitives): improve checksum algorithm #713

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23 changes: 16 additions & 7 deletions crates/primitives/src/bits/address.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -290,6 +290,15 @@ impl Address {
buf
}

// https://eips.ethereum.org/EIPS/eip-55
// > In English, convert the address to hex, but if the `i`th digit is a letter (ie. it’s one of
// > `abcdef`) print it in uppercase if the `4*i`th bit of the hash of the lowercase hexadecimal
// > address is 1 otherwise print it in lowercase.
//
// https://eips.ethereum.org/EIPS/eip-1191
// > [...] If the chain id passed to the function belongs to a network that opted for using this
// > checksum variant, prefix the address with the chain id and the `0x` separator before
// > calculating the hash. [...]
#[allow(clippy::wrong_self_convention)]
fn to_checksum_inner(&self, buf: &mut [u8; 42], chain_id: Option<u64>) {
buf[0] = b'0';
Expand All @@ -308,14 +317,14 @@ impl Address {
}
let hash = hasher.finalize();

let mut hash_hex = [0u8; 64];
hex::encode_to_slice(hash, &mut hash_hex).unwrap();

// `0..40` generates significantly less code than zipping or `array::into_iter`.
for i in 0..40 {
for (i, out) in buf[2..].iter_mut().enumerate() {
// This is made branchless for easier vectorization.
buf[2 + i] ^=
0b0010_0000 * (buf[2 + i].is_ascii_lowercase() & (hash_hex[i] >= b'8')) as u8;
// Get the i-th nibble of the hash.
let hash_nibble = hash[i / 2] >> (4 * (1 - i % 2)) & 0xf;
// Make the character ASCII uppercase if it's a hex letter and the hash nibble is >= 8.
// We can use a simpler comparison for checking if the character is a hex letter because
// we know `out` is a hex-encoded character (`b'0'..=b'9' | b'a'..=b'f'`).
*out ^= 0b0010_0000 * ((*out >= b'a') & (hash_nibble >= 8)) as u8;
}
}

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