1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// 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::fmt::{self, Write};
use core::iter::Fuse;
use core::ops::Range;
use tinyvec::TinyVec;

#[derive(Clone)]
enum DecompositionType {
    Canonical,
    Compatible,
}

/// External iterator for a string decomposition's characters.
#[derive(Clone)]
pub struct Decompositions<I> {
    kind: DecompositionType,
    iter: Fuse<I>,

    // This buffer stores pairs of (canonical combining class, character),
    // pushed onto the end in text order.
    //
    // It's divided into up to three sections:
    // 1) A prefix that is free space;
    // 2) "Ready" characters which are sorted and ready to emit on demand;
    // 3) A "pending" block which stills needs more characters for us to be able
    //    to sort in canonical order and is not safe to emit.
    buffer: TinyVec<[(u8, char); 4]>,
    ready: Range<usize>,
}

#[inline]
pub fn new_canonical<I: Iterator<Item = char>>(iter: I) -> Decompositions<I> {
    Decompositions {
        kind: self::DecompositionType::Canonical,
        iter: iter.fuse(),
        buffer: TinyVec::new(),
        ready: 0..0,
    }
}

#[inline]
pub fn new_compatible<I: Iterator<Item = char>>(iter: I) -> Decompositions<I> {
    Decompositions {
        kind: self::DecompositionType::Compatible,
        iter: iter.fuse(),
        buffer: TinyVec::new(),
        ready: 0..0,
    }
}

impl<I> Decompositions<I> {
    #[inline]
    fn push_back(&mut self, ch: char) {
        let class = super::char::canonical_combining_class(ch);

        if class == 0 {
            self.sort_pending();
        }

        self.buffer.push((class, ch));
    }

    #[inline]
    fn sort_pending(&mut self) {
        // NB: `sort_by_key` is stable, so it will preserve the original text's
        // order within a combining class.
        self.buffer[self.ready.end..].sort_by_key(|k| k.0);
        self.ready.end = self.buffer.len();
    }

    #[inline]
    fn reset_buffer(&mut self) {
        // Equivalent to `self.buffer.drain(0..self.ready.end)`
        // but faster than drain() if the buffer is a SmallVec or TinyVec
        let pending = self.buffer.len() - self.ready.end;
        for i in 0..pending {
            self.buffer[i] = self.buffer[i + self.ready.end];
        }
        self.buffer.truncate(pending);
        self.ready = 0..0;
    }

    #[inline]
    fn increment_next_ready(&mut self) {
        let next = self.ready.start + 1;
        if next == self.ready.end {
            self.reset_buffer();
        } else {
            self.ready.start = next;
        }
    }
}

impl<I: Iterator<Item = char>> Iterator for Decompositions<I> {
    type Item = char;

    #[inline]
    fn next(&mut self) -> Option<char> {
        while self.ready.end == 0 {
            match (self.iter.next(), &self.kind) {
                (Some(ch), &DecompositionType::Canonical) => {
                    super::char::decompose_canonical(ch, |d| self.push_back(d));
                }
                (Some(ch), &DecompositionType::Compatible) => {
                    super::char::decompose_compatible(ch, |d| self.push_back(d));
                }
                (None, _) => {
                    if self.buffer.is_empty() {
                        return None;
                    } else {
                        self.sort_pending();

                        // This implementation means that we can call `next`
                        // on an exhausted iterator; the last outer `next` call
                        // will result in an inner `next` call. To make this
                        // safe, we use `fuse`.
                        break;
                    }
                }
            }
        }

        // We can assume here that, if `self.ready.end` is greater than zero,
        // it's also greater than `self.ready.start`. That's because we only
        // increment `self.ready.start` inside `increment_next_ready`, and
        // whenever it reaches equality with `self.ready.end`, we reset both
        // to zero, maintaining the invariant that:
        //      self.ready.start < self.ready.end || self.ready.end == self.ready.start == 0
        //
        // This less-than-obviously-safe implementation is chosen for performance,
        // minimizing the number & complexity of branches in `next` in the common
        // case of buffering then unbuffering a single character with each call.
        let (_, ch) = self.buffer[self.ready.start];
        self.increment_next_ready();
        Some(ch)
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (lower, _) = self.iter.size_hint();
        (lower, None)
    }
}

impl<I: Iterator<Item = char> + Clone> fmt::Display for Decompositions<I> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for c in self.clone() {
            f.write_char(c)?;
        }
        Ok(())
    }
}