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
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205

// unsafe writing adapted from https://doc.rust-lang.org/src/alloc/vec/mod.rs.html#1878
use core::ptr::write;

use crate::shared::U8_MASK_BOT_6;

use super::alphabet::{
    BITS, WIDTH_1, WIDTH_10, WIDTH_2, WIDTH_3, WIDTH_4, WIDTH_5, WIDTH_6, WIDTH_7, WIDTH_8, WIDTH_9,
};

/// Capacity required in a `Vec<u8>` to encode this u64
#[inline]
pub const fn capacity_encode_u64(n: u64) -> usize {
    if let Some(log) = n.checked_ilog2() {
        1 + (log / 6) as usize
    } else {
        1
    }
}

/// Encode u64 with given encoding, into a `String`
///
/// Examples:
/// ```
/// use fast32::base64::RFC4648_NOPAD;
/// assert_eq!(RFC4648_NOPAD.encode_u64(31), "f");
/// ```
pub fn encode_u64(enc: &'static [u8; BITS], n: u64) -> String {
    let cap = capacity_encode_u64(n);
    let mut b = Vec::<u8>::with_capacity(cap);
    encode_u64_inner(enc, n, &mut b, cap, 0, cap);
    unsafe { String::from_utf8_unchecked(b) }
}

/// Encode u64 with given encoding, into an existing `Vec<u8>`
///
/// Example:
/// ```
/// use fast32::base64::RFC4648_NOPAD;
/// let mut b = Vec::<u8>::with_capacity(1);
/// RFC4648_NOPAD.encode_u64_into(31, &mut b);
/// assert_eq!(&b, b"f");
/// ```
///
/// Panics if not enough capacity in `b` for encoding -- see [`capacity_encode_u64`](self::capacity_encode_u64())
pub fn encode_u64_into(enc: &'static [u8; BITS], n: u64, b: &mut Vec<u8>) {
    let cap = capacity_encode_u64(n);
    let len = b.len();
    let new_len = len + cap;
    assert!(b.capacity() >= new_len, "Missing capacity for encoding");
    encode_u64_inner(enc, n, b, cap, len, new_len);
}

#[rustfmt::skip]
#[inline(always)]
fn encode_u64_inner(enc: &'static [u8; BITS], n: u64, b: &mut Vec<u8>, cap: usize, len: usize, new_len: usize) {
    match cap {
        11 => unsafe {
            let end = b.as_mut_ptr().add(len);

            // this top char is why u64 is diff output from normal bytes based base64
            // (other than multiples of 3 byte numbers):
            // for integer values (identifiers) we use remainder at the high bits, rather than low
            write(end        , enc[((n >> WIDTH_10) as u8               ) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_9) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_8) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_7) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_6) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 6), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 7), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 8), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 9), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add(10), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        10 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_9) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_8) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_7) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_6) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 6), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 7), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 8), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 9), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        9 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_8) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_7) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_6) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 6), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 7), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 8), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        8 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_7) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_6) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 6), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 7), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        7 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_6) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 6), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        6 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_5) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 5), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        5 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_4) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 4), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        4 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_3) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 3), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        3 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_2) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 2), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        2 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[((n >> WIDTH_1) as u8 & U8_MASK_BOT_6) as usize]);
            write(end.add( 1), enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        1 => unsafe {
            let end = b.as_mut_ptr().add(len);

            write(end        , enc[( n             as u8 & U8_MASK_BOT_6) as usize]);

            b.set_len(new_len);
        }

        _ => panic!("Inconceivable! Impossible length for u64")
    }
}