trezor-firmware/core/embed/rust/src/strutil.rs

pub fn hexlify(data: &[u8], buffer: &mut [u8]) {
    const HEX_LOWER: [u8; 16] = *b"0123456789abcdef";
    let mut i: usize = 0;
    for b in data.iter().take(buffer.len() / 2) {
        let hi: usize = ((b & 0xf0) >> 4).into();
        let lo: usize = (b & 0x0f).into();
        buffer[i] = HEX_LOWER[hi];
        buffer[i + 1] = HEX_LOWER[lo];
        i += 2;
    }
}