basexx 0.2.0

basexx utilities. base32, base64, base58, base56...
Documentation 
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use super::*;
use num_bigint::BigUint;

/*
 * ref.)
 *     https://en.wikipedia.org/wiki/Base56
*/

#[derive(Debug)]
pub struct Base56 {
    ags: AsciiGraphicSet,
}

impl Default for Base56 {
    fn default() -> Self {
        Base56::new()
    }
}

impl Base56 {
    pub fn new() -> Self {
        Self::with_slice(&_CMAP56)
    }
    pub fn with_str(a: &str) -> Self {
        assert_eq!(a.len(), 56);
        Self {
            ags: AsciiGraphicSet::with_str(a),
        }
    }
    pub fn with_slice(a: &[u8]) -> Self {
        assert_eq!(a.len(), 56);
        Self {
            ags: AsciiGraphicSet::with_slice(a),
        }
    }
}

impl Base56 {
    #[inline]
    pub fn encode(&self, a: &[u8]) -> Result<String, EncodeError> {
        _encode_base56(&self.ags, a)
    }
    #[inline]
    pub fn decode(&self, a: &str) -> Result<Vec<u8>, DecodeError> {
        _decode_base56(&self.ags, a)
    }
}

/*
 * Base56 format:
 *      A B C D E F G
 *                  +-- LSB
 *      +-------------- MSB
 *      bigendian
*/
#[inline(never)]
fn _encode_base56(ags: &AsciiGraphicSet, a: &[u8]) -> Result<String, EncodeError> {
    // encode binary
    let zero_count = a.iter().take_while(|&&x| x == 0).count();
    let mut oup = {
        let bigu = BigUint::from_bytes_be(&a[zero_count..]);
        let mut oup: Vec<u8> = bigu.to_radix_le(56);
        if zero_count > 0 {
            oup.resize(oup.len() + zero_count, 0u8);
        }
        oup.reverse();
        oup
    };
    // from binary to ascii
    ags.binary_to_ascii(&mut oup)?;
    let oup_sz = oup.len();
    // Safety: The encoding process strictly uses ASCII characters from AsciiGraphicSet.
    debug_assert!(std::str::from_utf8(&oup).is_ok());
    let string = unsafe { String::from_utf8_unchecked(oup) };
    assert!(string.len() == oup_sz);
    Ok(string)
}

#[inline(never)]
fn _decode_base56(ags: &AsciiGraphicSet, a: &str) -> Result<Vec<u8>, DecodeError> {
    // from ascii to binary
    let mut inp = a.as_bytes().to_vec();
    // from ascii to binary
    ags.ascii_to_binary(&mut inp)?;
    // decode binary
    let zero_count = inp.iter().take_while(|&&x| x == 0).count();
    let oup = {
        let bigu = BigUint::from_radix_be(&inp[zero_count..], 56).unwrap();
        let mut oup: Vec<u8> = bigu.to_bytes_le();
        if zero_count > 0 {
            oup.resize(oup.len() + zero_count, 0u8);
        }
        oup.reverse();
        oup
    };
    Ok(oup)
}

// exclusive ascii:
//     b'0' numeric zero, b'I' large ai, b'O' large o, b'l' small el
//     b'1' numeric one, b'o' small oh
const _CMAP56: [u8; 56] = [
    b'2', b'3', b'4', b'5', b'6', b'7', b'8', b'9', b'A', b'B', b'C', b'D', b'E', b'F', b'G', b'H',
    b'J', b'K', b'L', b'M', b'N', b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W', b'X', b'Y', b'Z',
    b'a', b'b', b'c', b'd', b'e', b'f', b'g', b'h', b'i', b'j', b'k', b'm', b'n', b'p', b'q', b'r',
    b's', b't', b'u', b'v', b'w', b'x', b'y', b'z',
];

#[cfg(all(test, not(feature = "bench")))]
mod tests;