// Copyright 2023 The Jujutsu Authors//// Licensed under the Apache License, Version 2.0 (the "License");// you may not use this file except in compliance with the License.// You may obtain a copy of the License at//// https://www.apache.org/licenses/LICENSE-2.0//// Unless required by applicable law or agreed to in writing, software// distributed under the License is distributed on an "AS IS" BASIS,// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.// See the License for the specific language governing permissions and// limitations under the License. //! Hex string helpers. const FORWARD_HEX_CHARS: &[u8; 16] = b"0123456789abcdef";const REVERSE_HEX_CHARS: &[u8; 16] = b"zyxwvutsrqponmlk"; fn forward_hex_value(b: u8) -> Option<u8> {    match b {        b'0'..=b'9' => Some(b - b'0'),        b'a'..=b'f' => Some(b - b'a' + 10),        b'A'..=b'F' => Some(b - b'A' + 10),        _ => None,    }} fn reverse_hex_value(b: u8) -> Option<u8> {    match b {        b'k'..=b'z' => Some(b'z' - b),        b'K'..=b'Z' => Some(b'Z' - b),        _ => None,    }} /// Decodes `hex` as normal hex string.pub fn decode_hex(hex: impl AsRef<[u8]>) -> Option<Vec<u8>> {    decode_hex_inner(hex.as_ref(), forward_hex_value)} /// Decodes `hex` as normal hex string prefix. The output may have odd-length/// byte. Returns `(bytes, has_odd_byte)`.pub fn decode_hex_prefix(hex: impl AsRef<[u8]>) -> Option<(Vec<u8>, bool)> {    decode_hex_prefix_inner(hex.as_ref(), forward_hex_value)} /// Decodes `reverse_hex` as hex string using `z-k` "digits".pub fn decode_reverse_hex(reverse_hex: impl AsRef<[u8]>) -> Option<Vec<u8>> {    decode_hex_inner(reverse_hex.as_ref(), reverse_hex_value)} /// Decodes `reverse_hex` as hex string prefix using `z-k` "digits". The output/// may have odd-length byte. Returns `(bytes, has_odd_byte)`.pub fn decode_reverse_hex_prefix(reverse_hex: impl AsRef<[u8]>) -> Option<(Vec<u8>, bool)> {    decode_hex_prefix_inner(reverse_hex.as_ref(), reverse_hex_value)} fn decode_hex_inner(reverse_hex: &[u8], hex_value: impl Fn(u8) -> Option<u8>) -> Option<Vec<u8>> {    if !reverse_hex.len().is_multiple_of(2) {        return None;    }    let (decoded, _) = decode_hex_prefix_inner(reverse_hex, hex_value)?;    Some(decoded)} fn decode_hex_prefix_inner(    reverse_hex: &[u8],    hex_value: impl Fn(u8) -> Option<u8>,) -> Option<(Vec<u8>, bool)> {    let mut decoded = Vec::with_capacity(usize::div_ceil(reverse_hex.len(), 2));    let (chunks, remainder) = reverse_hex.as_chunks();    for &[hi, lo] in chunks {        decoded.push(hex_value(hi)? << 4 | hex_value(lo)?);    }    if let &[hi] = remainder {        decoded.push(hex_value(hi)? << 4);        Some((decoded, true))    } else {        Some((decoded, false))    }} /// Encodes `data` as normal hex string.pub fn encode_hex(data: &[u8]) -> String {    encode_hex_inner(data, FORWARD_HEX_CHARS)} /// Encodes `data` as hex string using `z-k` "digits".pub fn encode_reverse_hex(data: &[u8]) -> String {    encode_hex_inner(data, REVERSE_HEX_CHARS)} fn encode_hex_inner(data: &[u8], chars: &[u8; 16]) -> String {    let encoded = data        .iter()        .flat_map(|b| [chars[usize::from(b >> 4)], chars[usize::from(b & 0xf)]])        .collect();    String::from_utf8(encoded).unwrap()} /// Calculates common prefix length of two byte sequences. The length/// to be returned is a number of hexadecimal digits.pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {    std::iter::zip(bytes_a, bytes_b)        .enumerate()        .find_map(|(i, (a, b))| match a ^ b {            0 => None,            d if d & 0xf0 == 0 => Some(i * 2 + 1),            _ => Some(i * 2),        })        .unwrap_or_else(|| bytes_a.len().min(bytes_b.len()) * 2)} #[cfg(test)]mod tests {    use super::*;     #[test]    fn test_forward_hex() {        // Empty string        assert_eq!(decode_hex(""), Some(vec![]));        assert_eq!(decode_hex_prefix(""), Some((vec![], false)));        assert_eq!(encode_hex(b""), "".to_string());         // Single digit        assert_eq!(decode_hex("0"), None);        assert_eq!(decode_hex_prefix("f"), Some((vec![0xf0], true)));         // All digits        assert_eq!(            decode_hex("0123456789abcDEF"),            Some(b"\x01\x23\x45\x67\x89\xab\xcd\xef".to_vec())        );        assert_eq!(            decode_hex_prefix("0123456789ABCdef"),            Some((b"\x01\x23\x45\x67\x89\xab\xcd\xef".to_vec(), false))        );        assert_eq!(            encode_hex(b"\x01\x23\x45\x67\x89\xab\xcd\xef"),            "0123456789abcdef".to_string()        );         // Invalid digit        assert_eq!(decode_hex("gg"), None);        assert_eq!(decode_hex_prefix("gg"), None);    }     #[test]    fn test_reverse_hex() {        // Empty string        assert_eq!(decode_reverse_hex(""), Some(vec![]));        assert_eq!(decode_reverse_hex_prefix(""), Some((vec![], false)));        assert_eq!(encode_reverse_hex(b""), "".to_string());         // Single digit        assert_eq!(decode_reverse_hex("z"), None);        assert_eq!(decode_reverse_hex_prefix("k"), Some((vec![0xf0], true)));         // All digits        assert_eq!(            decode_reverse_hex("zyxwvutsRQPONMLK"),            Some(b"\x01\x23\x45\x67\x89\xab\xcd\xef".to_vec())        );        assert_eq!(            decode_reverse_hex_prefix("ZYXWVUTSrqponmlk"),            Some((b"\x01\x23\x45\x67\x89\xab\xcd\xef".to_vec(), false))        );        assert_eq!(            encode_reverse_hex(b"\x01\x23\x45\x67\x89\xab\xcd\xef"),            "zyxwvutsrqponmlk".to_string()        );         // Invalid digit        assert_eq!(decode_reverse_hex("jj"), None);        assert_eq!(decode_reverse_hex_prefix("jj"), None);    }}