| // Copyright 2017 The UNIC Project Developers. |
| // |
| // See the COPYRIGHT file at the top-level directory of this distribution. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| use core::char; |
| |
| pub const BEFORE_SURROGATE: char = '\u{D7FF}'; |
| pub const AFTER_SURROGATE: char = '\u{E000}'; |
| |
| #[inline] |
| #[allow(unsafe_code)] |
| /// Step a character one step towards `char::MAX`. |
| /// |
| /// # Safety |
| /// |
| /// If the given character is `char::MAX`, the return value is not a valid character. |
| pub unsafe fn forward(ch: char) -> char { |
| if ch == BEFORE_SURROGATE { |
| AFTER_SURROGATE |
| } else { |
| char::from_u32_unchecked(ch as u32 + 1) |
| } |
| } |
| |
| #[inline] |
| #[allow(unsafe_code)] |
| /// Step a character one step towards `'\0'`. |
| /// |
| /// # Safety |
| /// |
| /// If the given character is `'\0'`, this will cause an underflow. |
| /// (Thus, it will panic in debug mode, undefined behavior in release mode.) |
| pub unsafe fn backward(ch: char) -> char { |
| if ch == AFTER_SURROGATE { |
| BEFORE_SURROGATE |
| } else { |
| char::from_u32_unchecked(ch as u32 - 1) |
| } |
| } |
