ilyagr.bsky.social
just playing with tangled
1// Copyright 2023 The Jujutsu Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15#![allow(missing_docs)]
16
17const REVERSE_HEX_CHARS: &[u8; 16] = b"zyxwvutsrqponmlk";
18
19fn to_forward_hex_digit(b: u8) -> Option<u8> {
20 let value = match b {
21 b'k'..=b'z' => b'z' - b,
22 b'K'..=b'Z' => b'Z' - b,
23 _ => return None,
24 };
25 if value < 10 {
26 Some(b'0' + value)
27 } else {
28 Some(b'a' + value - 10)
29 }
30}
31
32pub fn to_forward_hex(reverse_hex: &str) -> Option<String> {
33 reverse_hex
34 .bytes()
35 .map(|b| to_forward_hex_digit(b).map(char::from))
36 .collect()
37}
38
39/// Encodes `data` as hex string using `z-k` "digits".
40pub fn encode_reverse_hex(data: &[u8]) -> String {
41 let chars = REVERSE_HEX_CHARS;
42 let encoded = data
43 .iter()
44 .flat_map(|b| [chars[usize::from(b >> 4)], chars[usize::from(b & 0xf)]])
45 .collect();
46 String::from_utf8(encoded).unwrap()
47}
48
49/// Calculates common prefix length of two byte sequences. The length
50/// to be returned is a number of hexadecimal digits.
51pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {
52 std::iter::zip(bytes_a, bytes_b)
53 .enumerate()
54 .find_map(|(i, (a, b))| match a ^ b {
55 0 => None,
56 d if d & 0xf0 == 0 => Some(i * 2 + 1),
57 _ => Some(i * 2),
58 })
59 .unwrap_or_else(|| bytes_a.len().min(bytes_b.len()) * 2)
60}
61
62#[cfg(test)]
63mod tests {
64 use super::*;
65
66 #[test]
67 fn test_reverse_hex() {
68 // Empty string
69 assert_eq!(encode_reverse_hex(b""), "".to_string());
70 assert_eq!(to_forward_hex(""), Some("".to_string()));
71
72 // Single digit
73 assert_eq!(to_forward_hex("z"), Some("0".to_string()));
74
75 // All digits
76 assert_eq!(
77 encode_reverse_hex(b"\x01\x23\x45\x67\x89\xab\xcd\xef"),
78 "zyxwvutsrqponmlk".to_string()
79 );
80 assert_eq!(
81 to_forward_hex("zyxwvutsrqponmlkPONMLK"),
82 Some("0123456789abcdefabcdef".to_string())
83 );
84
85 // Invalid digit
86 assert_eq!(to_forward_hex("j"), None);
87 }
88}