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) -> char23pub 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) -> char39pub 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