// 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. #![allow(missing_docs)] fn to_reverse_hex_digit(b: u8) -> Option<u8> {    let value = match b {        b'0'..=b'9' => b - b'0',        b'A'..=b'F' => b - b'A' + 10,        b'a'..=b'f' => b - b'a' + 10,        _ => return None,    };    Some(b'z' - value)} fn to_forward_hex_digit(b: u8) -> Option<u8> {    let value = match b {        b'k'..=b'z' => b'z' - b,        b'K'..=b'Z' => b'Z' - b,        _ => return None,    };    if value < 10 {        Some(b'0' + value)    } else {        Some(b'a' + value - 10)    }} pub fn to_forward_hex(reverse_hex: &str) -> Option<String> {    reverse_hex        .bytes()        .map(|b| to_forward_hex_digit(b).map(char::from))        .collect()} pub fn to_reverse_hex(forward_hex: &str) -> Option<String> {    forward_hex        .bytes()        .map(|b| to_reverse_hex_digit(b).map(char::from))        .collect()} /// Calculates common prefix length of two bytes. The length to be returned is/// a number of hexadecimal digits.pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {    iter_half_bytes(bytes_a)        .zip(iter_half_bytes(bytes_b))        .take_while(|(a, b)| a == b)        .count()} fn iter_half_bytes(bytes: &[u8]) -> impl ExactSizeIterator<Item = u8> + '_ {    (0..bytes.len() * 2).map(|i| {        let v = bytes[i / 2];        if i & 1 == 0 {            v >> 4        } else {            v & 0xf        }    })} #[cfg(test)]#[cfg(test)]mod tests {    use super::*;     #[test]    fn test_reverse_hex() {        // Empty string        assert_eq!(to_reverse_hex(""), Some("".to_string()));        assert_eq!(to_forward_hex(""), Some("".to_string()));         // Single digit        assert_eq!(to_reverse_hex("0"), Some("z".to_string()));        assert_eq!(to_forward_hex("z"), Some("0".to_string()));         // All digits        assert_eq!(            to_reverse_hex("0123456789abcdefABCDEF"),            Some("zyxwvutsrqponmlkponmlk".to_string())        );        assert_eq!(            to_forward_hex("zyxwvutsrqponmlkPONMLK"),            Some("0123456789abcdefabcdef".to_string())        );         // Invalid digit        assert_eq!(to_reverse_hex("g"), None);        assert_eq!(to_forward_hex("j"), None);    }}