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| 1 | +// Copyright 2012-2015 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 | +use core::fmt::{self, Write}; |
| 11 | +use core::iter::Fuse; |
| 12 | +use core::ops::Range; |
| 13 | +use smallvec::SmallVec; |
| 14 | + |
| 15 | +#[derive(Clone)] |
| 16 | +enum DecompositionType { |
| 17 | + Canonical, |
| 18 | + Compatible, |
| 19 | +} |
| 20 | + |
| 21 | +/// External iterator for a string decomposition's characters. |
| 22 | +#[derive(Clone)] |
| 23 | +pub struct DecompositionsAlignment<I> { |
| 24 | + kind: DecompositionType, |
| 25 | + iter: Fuse<I>, |
| 26 | + |
| 27 | + // This buffer stores pairs of (canonical combining class, character), |
| 28 | + // pushed onto the end in text order. |
| 29 | + // |
| 30 | + // It's divided into up to three sections: |
| 31 | + // 1) A prefix that is free space; |
| 32 | + // 2) "Ready" characters which are sorted and ready to emit on demand; |
| 33 | + // 3) A "pending" block which stills needs more characters for us to be able |
| 34 | + // to sort in canonical order and is not safe to emit. |
| 35 | + buffer: SmallVec<[(u8, char, isize); 4]>, |
| 36 | + ready: Range<usize>, |
| 37 | +} |
| 38 | + |
| 39 | +#[inline] |
| 40 | +pub fn new_canonical<I: Iterator<Item = char>>(iter: I) -> DecompositionsAlignment<I> { |
| 41 | + DecompositionsAlignment { |
| 42 | + kind: self::DecompositionType::Canonical, |
| 43 | + iter: iter.fuse(), |
| 44 | + buffer: Default::default(), |
| 45 | + ready: 0..0, |
| 46 | + } |
| 47 | +} |
| 48 | + |
| 49 | +#[inline] |
| 50 | +pub fn new_compatible<I: Iterator<Item = char>>(iter: I) -> DecompositionsAlignment<I> { |
| 51 | + DecompositionsAlignment { |
| 52 | + kind: self::DecompositionType::Compatible, |
| 53 | + iter: iter.fuse(), |
| 54 | + buffer: Default::default(), |
| 55 | + ready: 0..0, |
| 56 | + } |
| 57 | +} |
| 58 | + |
| 59 | +impl<I> DecompositionsAlignment<I> { |
| 60 | + #[inline] |
| 61 | + fn push_back(&mut self, ch: char, first: bool) { |
| 62 | + let class = super::char::canonical_combining_class(ch); |
| 63 | + |
| 64 | + if class == 0 { |
| 65 | + self.sort_pending(); |
| 66 | + self.buffer.push((class, ch, if first { 0 } else { 1 })); |
| 67 | + self.ready.end = self.buffer.len(); |
| 68 | + } else { |
| 69 | + self.buffer.push((class, ch, if first { 0 } else { 1 })); |
| 70 | + } |
| 71 | + } |
| 72 | + |
| 73 | + #[inline] |
| 74 | + fn sort_pending(&mut self) { |
| 75 | + // NB: `sort_by_key` is stable, so it will preserve the original text's |
| 76 | + // order within a combining class. |
| 77 | + self.buffer[self.ready.end..].sort_by_key(|k| k.0); |
| 78 | + } |
| 79 | + |
| 80 | + #[inline] |
| 81 | + fn reset_buffer(&mut self) { |
| 82 | + // Equivalent to `self.buffer.drain(0..self.ready.end)` |
| 83 | + // but faster than drain() if the buffer is a SmallVec or TinyVec |
| 84 | + let pending = self.buffer.len() - self.ready.end; |
| 85 | + for i in 0..pending { |
| 86 | + self.buffer[i] = self.buffer[i + self.ready.end]; |
| 87 | + } |
| 88 | + self.buffer.truncate(pending); |
| 89 | + self.ready = 0..0; |
| 90 | + } |
| 91 | + |
| 92 | + #[inline] |
| 93 | + fn increment_next_ready(&mut self) { |
| 94 | + let next = self.ready.start + 1; |
| 95 | + if next == self.ready.end { |
| 96 | + self.reset_buffer(); |
| 97 | + } else { |
| 98 | + self.ready.start = next; |
| 99 | + } |
| 100 | + } |
| 101 | +} |
| 102 | + |
| 103 | +impl<I: Iterator<Item = char>> Iterator for DecompositionsAlignment<I> { |
| 104 | + type Item = (char, isize); |
| 105 | + |
| 106 | + #[inline] |
| 107 | + fn next(&mut self) -> Option<Self::Item> { |
| 108 | + while self.ready.end == 0 { |
| 109 | + match (self.iter.next(), &self.kind) { |
| 110 | + (Some(ch), &DecompositionType::Canonical) => { |
| 111 | + let mut first = true; |
| 112 | + super::char::decompose_canonical(ch, |d| { |
| 113 | + self.push_back(d, first); |
| 114 | + first = false; |
| 115 | + }); |
| 116 | + } |
| 117 | + (Some(ch), &DecompositionType::Compatible) => { |
| 118 | + let mut first = true; |
| 119 | + super::char::decompose_compatible(ch, |d| { |
| 120 | + self.push_back(d, first); |
| 121 | + first = false; |
| 122 | + }); |
| 123 | + } |
| 124 | + (None, _) => { |
| 125 | + if self.buffer.is_empty() { |
| 126 | + return None; |
| 127 | + } |
| 128 | + self.sort_pending(); |
| 129 | + self.ready.end = self.buffer.len(); |
| 130 | + |
| 131 | + // This implementation means that we can call `next` |
| 132 | + // on an exhausted iterator; the last outer `next` call |
| 133 | + // will result in an inner `next` call. To make this |
| 134 | + // safe, we use `fuse`. |
| 135 | + break; |
| 136 | + } |
| 137 | + } |
| 138 | + } |
| 139 | + |
| 140 | + // We can assume here that, if `self.ready.end` is greater than zero, |
| 141 | + // it's also greater than `self.ready.start`. That's because we only |
| 142 | + // increment `self.ready.start` inside `increment_next_ready`, and |
| 143 | + // whenever it reaches equality with `self.ready.end`, we reset both |
| 144 | + // to zero, maintaining the invariant that: |
| 145 | + // self.ready.start < self.ready.end || self.ready.end == self.ready.start == 0 |
| 146 | + // |
| 147 | + // This less-than-obviously-safe implementation is chosen for performance, |
| 148 | + // minimizing the number & complexity of branches in `next` in the common |
| 149 | + // case of buffering then unbuffering a single character with each call. |
| 150 | + let (_, ch, size) = self.buffer[self.ready.start]; |
| 151 | + self.increment_next_ready(); |
| 152 | + Some((ch, size)) |
| 153 | + } |
| 154 | + |
| 155 | + fn size_hint(&self) -> (usize, Option<usize>) { |
| 156 | + let (lower, _) = self.iter.size_hint(); |
| 157 | + (lower, None) |
| 158 | + } |
| 159 | +} |
| 160 | + |
| 161 | +impl<I: Iterator<Item = char> + Clone> fmt::Display for DecompositionsAlignment<I> { |
| 162 | + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 163 | + for (c, _) in self.clone() { |
| 164 | + f.write_char(c)?; |
| 165 | + } |
| 166 | + Ok(()) |
| 167 | + } |
| 168 | +} |
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