Method encode_to_base58

publication/code/chapter10/base58.rs:45–99

(&self)

// 实现 base58 编码
impl Encoder for str {
    fn encode_to_base58(&self) -> String {
        // 转换为 bytes 来处理
        let str_u8 = self.as_bytes();

        // 统计前置 0 个数
        let zero_count = str_u8.iter()
                               .take_while(|&&x| x == 0)
                               .count();

        // 转换后所需空间：log(256)/log(58) 约为原数据 1.38 倍
        // 前置 0 不需要，所以要减去
        let size = (str_u8.len() - zero_count) * 138 / 100 + 1;

        // 字符进制转换
        let mut i = zero_count;
        let mut high = size - 1;
        let mut buffer = vec![0u8; size];
        while i < str_u8.len() {
            // j 为逐渐减小的下标，对应从后往前
            let mut j = size - 1;

            // carry 为从前往后读取的字符
            let mut carry = str_u8[i] as u32;

            // 将数据从后往前依次存放
            while j > high || carry != 0 {
                carry += 256 * buffer[j] as u32;
                buffer[j] = (carry % BIG_RADIX) as u8;
                carry /= BIG_RADIX;

                if j  > 0 {
                    j -= 1;
                }
            }

            i += 1;
            high = j;
        }

        // 处理多个前置 0
        let mut b58_str = String::new();
        for _ in 0..zero_count {
            b58_str.push(ALPHABET_INDEX_0);
        }

        // 获取编码后的字符并拼接成字符串
        let mut j = buffer.iter().take_while(|&&x| x == 0).count();
        while j < size {
            b58_str.push(ALPHABET[buffer[j] as usize] as char);
            j += 1;
        }

        // 返回编码后字符串
        b58_str
    }
}

// 实现 base58 解码