2023-01-11 09:57:03 +01:00
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/*
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*
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* Copyright (c) 2020-2022 Project CHIP Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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2023-01-11 09:54:12 +01:00
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//! Base38 encoding functions.
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2023-01-11 09:57:03 +01:00
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2023-01-10 21:01:02 +01:00
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const BASE38_CHARS: &str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-.";
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2023-01-11 09:54:12 +01:00
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/// Encodes a byte array into a base38 string.
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2023-01-12 15:42:21 +01:00
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pub fn encode(bytes: &[u8], length: usize) -> String {
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2023-01-10 21:01:02 +01:00
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let mut offset = 0;
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let mut result = String::new();
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while offset < length {
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let remaining = length - offset;
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match remaining.cmp(&2) {
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std::cmp::Ordering::Greater => {
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result.push_str(&encode_base38(
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((bytes[offset + 2] as u32) << 16)
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| ((bytes[offset + 1] as u32) << 8)
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| (bytes[offset] as u32),
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5,
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));
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offset += 3;
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}
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std::cmp::Ordering::Equal => {
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result.push_str(&encode_base38(
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((bytes[offset + 1] as u32) << 8) | (bytes[offset] as u32),
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4,
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));
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break;
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}
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std::cmp::Ordering::Less => {
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result.push_str(&encode_base38(bytes[offset] as u32, 2));
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break;
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}
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}
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}
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result
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}
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2023-01-10 21:25:05 +01:00
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2023-01-11 09:54:12 +01:00
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fn encode_base38(mut value: u32, char_count: u8) -> String {
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let mut result = String::new();
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2023-01-13 11:40:16 +01:00
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let chars = BASE38_CHARS.chars();
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2023-01-11 09:54:12 +01:00
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for _ in 0..char_count {
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2023-01-13 11:40:16 +01:00
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let mut use_chars = chars.clone();
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2023-01-11 09:54:12 +01:00
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let remainder = value % 38;
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2023-01-13 11:40:16 +01:00
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result.push(use_chars.nth(remainder as usize).unwrap());
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2023-01-11 09:54:12 +01:00
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value = (value - remainder) / 38;
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}
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result
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}
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2023-01-10 21:25:05 +01:00
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn can_base38_encode() {
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const ENCODED: &str = "-MOA57ZU02IT2L2BJ00";
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const DECODED: [u8; 11] = [
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0x88, 0xff, 0xa7, 0x91, 0x50, 0x40, 0x00, 0x47, 0x51, 0xdd, 0x02,
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];
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2023-01-12 15:42:21 +01:00
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assert_eq!(encode(&DECODED, 11), ENCODED);
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2023-01-10 21:25:05 +01:00
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}
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}
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