nordisk/heimdall

crates/heimdall-core/src/hex.rs

// SPDX-License-Identifier: AGPL-3.0-only
// Copyright (C) 2026 Ignalina ApS and Vetra Automation AB

//! Lower-case hex, strict on input (even length, `0-9a-fA-F` only).

const DIGITS: &[u8; 16] = b"0123456789abcdef";

/// Lower-case hex of `bytes`.
pub fn encode(bytes: &[u8]) -> String {
    let mut s = String::with_capacity(bytes.len() * 2);
    for b in bytes {
        s.push(DIGITS[(b >> 4) as usize] as char);
        s.push(DIGITS[(b & 0x0f) as usize] as char);
    }
    s
}

fn nibble(c: u8) -> Option<u8> {
    match c {
        b'0'..=b'9' => Some(c - b'0'),
        b'a'..=b'f' => Some(c - b'a' + 10),
        b'A'..=b'F' => Some(c - b'A' + 10),
        _ => None,
    }
}

/// Decode hex; `None` on odd length or a non-hex character.
pub fn decode(s: &str) -> Option<Vec<u8>> {
    let b = s.as_bytes();
    if b.len() % 2 != 0 {
        return None;
    }
    b.chunks_exact(2)
        .map(|p| Some((nibble(p[0])? << 4) | nibble(p[1])?))
        .collect()
}