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: u32 = ch as u32;
35 if code < MAX_ONE_B && len >= 1 {
36 ptr.add(0).write(val: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
93