1 // Copyright 2017 The UNIC Project Developers.
2 //
3 // See the COPYRIGHT file at the top-level directory of this distribution.
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 use core::char;
12 
13 pub const BEFORE_SURROGATE: char = '\u{D7FF}';
14 pub const AFTER_SURROGATE: char = '\u{E000}';
15 
16 #[inline]
17 #[allow(unsafe_code)]
18 /// Step a character one step towards `char::MAX`.
19 ///
20 /// # Safety
21 ///
22 /// If the given character is `char::MAX`, the return value is not a valid character.
forward(ch: char) -> char23 pub unsafe fn forward(ch: char) -> char {
24     if ch == BEFORE_SURROGATE {
25         AFTER_SURROGATE
26     } else {
27         char::from_u32_unchecked(ch as u32 + 1)
28     }
29 }
30 
31 #[inline]
32 #[allow(unsafe_code)]
33 /// Step a character one step towards `'\0'`.
34 ///
35 /// # Safety
36 ///
37 /// If the given character is `'\0'`, this will cause an underflow.
38 /// (Thus, it will panic in debug mode, undefined behavior in release mode.)
backward(ch: char) -> char39 pub unsafe fn backward(ch: char) -> char {
40     if ch == AFTER_SURROGATE {
41         BEFORE_SURROGATE
42     } else {
43         char::from_u32_unchecked(ch as u32 - 1)
44     }
45 }
46