arrayvec/
char.rs

1// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
2// file at the top-level directory of this distribution and at
3// http://rust-lang.org/COPYRIGHT.
4//
5// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8// option. This file may not be copied, modified, or distributed
9// except according to those terms.
10//
11// Original authors: alexchrichton, bluss
12
13// UTF-8 ranges and tags for encoding characters
14const TAG_CONT: u8    = 0b1000_0000;
15const TAG_TWO_B: u8   = 0b1100_0000;
16const TAG_THREE_B: u8 = 0b1110_0000;
17const TAG_FOUR_B: u8  = 0b1111_0000;
18const MAX_ONE_B: u32   =     0x80;
19const MAX_TWO_B: u32   =    0x800;
20const MAX_THREE_B: u32 =  0x10000;
21
22/// Placeholder
23pub struct EncodeUtf8Error;
24
25/// Encode a char into buf using UTF-8.
26///
27/// On success, return the byte length of the encoding (1, 2, 3 or 4).<br>
28/// On error, return `EncodeUtf8Error` if the buffer was too short for the char.
29///
30/// Safety: `ptr` must be writable for `len` bytes.
31#[inline]
32pub unsafe fn encode_utf8(ch: char, ptr: *mut u8, len: usize) -> Result<usize, EncodeUtf8Error>
33{
34    let code = ch as u32;
35    if code < MAX_ONE_B && len >= 1 {
36        ptr.add(0).write(code as u8);
37        return Ok(1);
38    } else if code < MAX_TWO_B && len >= 2 {
39        ptr.add(0).write((code >> 6 & 0x1F) as u8 | TAG_TWO_B);
40        ptr.add(1).write((code & 0x3F) as u8 | TAG_CONT);
41        return Ok(2);
42    } else if code < MAX_THREE_B && len >= 3 {
43        ptr.add(0).write((code >> 12 & 0x0F) as u8 | TAG_THREE_B);
44        ptr.add(1).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
45        ptr.add(2).write((code & 0x3F) as u8 | TAG_CONT);
46        return Ok(3);
47    } else if len >= 4 {
48        ptr.add(0).write((code >> 18 & 0x07) as u8 | TAG_FOUR_B);
49        ptr.add(1).write((code >> 12 & 0x3F) as u8 | TAG_CONT);
50        ptr.add(2).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
51        ptr.add(3).write((code & 0x3F) as u8 | TAG_CONT);
52        return Ok(4);
53    };
54    Err(EncodeUtf8Error)
55}
56
57
58#[test]
59#[cfg_attr(miri, ignore)] // Miri is too slow
60fn test_encode_utf8() {
61    // Test that all codepoints are encoded correctly
62    let mut data = [0u8; 16];
63    for codepoint in 0..=(std::char::MAX as u32) {
64        if let Some(ch) = std::char::from_u32(codepoint) {
65            for elt in &mut data { *elt = 0; }
66            let ptr = data.as_mut_ptr();
67            let len = data.len();
68            unsafe {
69                let res = encode_utf8(ch, ptr, len).ok().unwrap();
70                assert_eq!(res, ch.len_utf8());
71            }
72            let string = std::str::from_utf8(&data).unwrap();
73            assert_eq!(string.chars().next(), Some(ch));
74        }
75    }
76}
77
78#[test]
79fn test_encode_utf8_oob() {
80    // test that we report oob if the buffer is too short
81    let mut data = [0u8; 16];
82    let chars = ['a', 'α', '�', '𐍈'];
83    for (len, &ch) in (1..=4).zip(&chars) {
84        assert_eq!(len, ch.len_utf8(), "Len of ch={}", ch);
85        let ptr = data.as_mut_ptr();
86        unsafe {
87            assert!(matches::matches!(encode_utf8(ch, ptr, len - 1), Err(_)));
88            assert!(matches::matches!(encode_utf8(ch, ptr, len), Ok(_)));
89        }
90    }
91}
92
arrayvec/char.rs

arrayvec/
char.rs
