fast32 1.0.3

Base32 and base64 encoding in Rust. Primarily for integer (u64, u128) and UUID identifiers, as well as arbitrary byte arrays.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

use core::ptr::write;

use crate::shared::{bits_or_err_u8, DecodeError};

use super::alphabet::{WIDTH_DEC, WIDTH_ENC};

/// Capacity needed in dest `Vec<u8>` to decode this byte array -- without padding!
///
/// Also see padded [`capacity_decode`](super::Alphabet64Padded::capacity_decode())
#[inline]
pub const fn capacity_decode(a: &[u8]) -> usize {
    a.len() * WIDTH_DEC / WIDTH_ENC
}

#[inline]
const fn rem_dec(rem: usize) -> usize {
    match rem {
        3 => 2,
        2 => 1,
        _ => 0,
    }
}

/// Decode byte array with given decoding, into a `Vec<u8>`
///
/// Example:
/// ```
/// use fast32::base64::RFC4648;
/// assert_eq!(RFC4648.decode(b"ABI=").unwrap(), &[0x00, 0x12]);
/// ```
///
/// Returns [`DecodeError`] if input to decode is invalid
pub fn decode(dec: &'static [u8; 256], a: &[u8]) -> Result<Vec<u8>, DecodeError> {
    let len_enc = a.len();
    let rem = len_enc % WIDTH_ENC;
    let max = len_enc / WIDTH_ENC;

    let c_max = max * WIDTH_DEC;
    let rem_dec = rem_dec(rem);

    let mut b = Vec::<u8>::with_capacity(c_max + rem_dec);

    decode_inner(dec, a, &mut b, max, 0, c_max, rem, rem_dec, len_enc)?;

    Ok(b)
}

/// Decode byte array with given decoding, into an existing `Vec<u8>`
///
/// Example:
/// ```
/// use fast32::base64::RFC4648;
/// let mut b = Vec::<u8>::with_capacity(2);
/// RFC4648.decode_into(b"ABI=", &mut b);
/// assert_eq!(&b, &[0x00, 0x12]);
/// ```
///
/// Returns [`DecodeError`] if input to decode is invalid
///
/// Panics if not enough capacity in `b` for decoding -- see [`capacity_decode`](self::capacity_decode())
pub fn decode_into(dec: &'static [u8; 256], a: &[u8], b: &mut Vec<u8>) -> Result<(), DecodeError> {
    let len_enc = a.len();
    let rem = len_enc % WIDTH_ENC;
    let max = len_enc / WIDTH_ENC;

    let len_dec = b.len();
    let c_max = len_dec + max * WIDTH_DEC;
    let rem_dec = rem_dec(rem);

    assert!(
        b.capacity() >= c_max + rem_dec,
        "Missing capacity for decoding"
    );

    decode_inner(dec, a, b, max, len_dec, c_max, rem, rem_dec, len_enc)
}

#[rustfmt::skip]
#[inline(always)]
fn decode_inner(dec: &'static [u8; 256], a: &[u8], b: &mut Vec<u8>, max: usize, len_dec: usize, c_max: usize, rem: usize, rem_dec: usize, len_enc: usize) -> Result<(), DecodeError> {
    for i in 0..max {
        let c = len_dec + i * WIDTH_DEC;
        let p = i * WIDTH_ENC;

        let p1 = bits_or_err_u8(dec, a, p  )?;
        let p2 = bits_or_err_u8(dec, a, p+1)?;
        let p3 = bits_or_err_u8(dec, a, p+2)?;
        let p4 = bits_or_err_u8(dec, a, p+3)?;

        unsafe {
            let end = b.as_mut_ptr().add(c);

            write(end       , (p1 << 2) | (p2 >> 4));
            write(end.add(1), (p2 << 4) | (p3 >> 2));
            write(end.add(2), (p3 << 6) |  p4      );

            b.set_len(c + WIDTH_DEC);
        }
    }

    match rem {
        3 => {
            let p = max * WIDTH_ENC;

            let p1 = bits_or_err_u8(dec, a, p  )?;
            let p2 = bits_or_err_u8(dec, a, p+1)?;
            let p3 = bits_or_err_u8(dec, a, p+2)?;

            if p3 & 0b0011 != 0 {
                Err(DecodeError::InvalidChar { char: a[p+2] as char, index: p+2 })?
            }

            unsafe {
                let end = b.as_mut_ptr().add(c_max);

                write(end       , (p1 << 2) | (p2 >> 4));
                write(end.add(1), (p2 << 4) | (p3 >> 2));

                b.set_len(c_max + rem_dec);
            }
        }
        2 => {
            let p = max * WIDTH_ENC;

            let p1 = bits_or_err_u8(dec, a, p  )?;
            let p2 = bits_or_err_u8(dec, a, p+1)?;

            if p2 & 0b1111 != 0 {
                Err(DecodeError::InvalidChar { char: a[p+1] as char, index: p+1 })?
            }

            unsafe {
                let end = b.as_mut_ptr().add(c_max);

                write(end       , (p1 << 2) | (p2 >> 4));

                b.set_len(c_max + rem_dec);
            }
        }
        0 => {}
        _ => Err(DecodeError::InvalidLength { length: len_enc })?
    }

    Ok(())
}