DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (c68fe15a81fc)

VCS Links

Line Code
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186
// Copyright 2015 The Servo 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.

//! 3.3.2 Explicit Levels and Directions
//!
//! <http://www.unicode.org/reports/tr9/#Explicit_Levels_and_Directions>

use super::char_data::{BidiClass, is_rtl};
use super::level::Level;

use BidiClass::*;

/// Compute explicit embedding levels for one paragraph of text (X1-X8).
///
/// `processing_classes[i]` must contain the `BidiClass` of the char at byte index `i`,
/// for each char in `text`.
#[cfg_attr(feature = "flame_it", flame)]
pub fn compute(
    text: &str,
    para_level: Level,
    original_classes: &[BidiClass],
    levels: &mut [Level],
    processing_classes: &mut [BidiClass],
) {
    assert_eq!(text.len(), original_classes.len());

    // <http://www.unicode.org/reports/tr9/#X1>
    let mut stack = DirectionalStatusStack::new();
    stack.push(para_level, OverrideStatus::Neutral);

    let mut overflow_isolate_count = 0u32;
    let mut overflow_embedding_count = 0u32;
    let mut valid_isolate_count = 0u32;

    for (i, c) in text.char_indices() {
        match original_classes[i] {

            // Rules X2-X5c
            RLE | LRE | RLO | LRO | RLI | LRI | FSI => {
                let last_level = stack.last().level;

                // X5a-X5c: Isolate initiators get the level of the last entry on the stack.
                let is_isolate = matches!(original_classes[i], RLI | LRI | FSI);
                if is_isolate {
                    levels[i] = last_level;
                    match stack.last().status {
                        OverrideStatus::RTL => processing_classes[i] = R,
                        OverrideStatus::LTR => processing_classes[i] = L,
                        _ => {}
                    }
                }

                let new_level = if is_rtl(original_classes[i]) {
                    last_level.new_explicit_next_rtl()
                } else {
                    last_level.new_explicit_next_ltr()
                };
                if new_level.is_ok() && overflow_isolate_count == 0 &&
                    overflow_embedding_count == 0
                {
                    let new_level = new_level.unwrap();
                    stack.push(
                        new_level,
                        match original_classes[i] {
                            RLO => OverrideStatus::RTL,
                            LRO => OverrideStatus::LTR,
                            RLI | LRI | FSI => OverrideStatus::Isolate,
                            _ => OverrideStatus::Neutral,
                        },
                    );
                    if is_isolate {
                        valid_isolate_count += 1;
                    } else {
                        // The spec doesn't explicitly mention this step, but it is necessary.
                        // See the reference implementations for comparison.
                        levels[i] = new_level;
                    }
                } else if is_isolate {
                    overflow_isolate_count += 1;
                } else if overflow_isolate_count == 0 {
                    overflow_embedding_count += 1;
                }
            }

            // <http://www.unicode.org/reports/tr9/#X6a>
            PDI => {
                if overflow_isolate_count > 0 {
                    overflow_isolate_count -= 1;
                } else if valid_isolate_count > 0 {
                    overflow_embedding_count = 0;
                    loop {
                        // Pop everything up to and including the last Isolate status.
                        match stack.vec.pop() {
                            None |
                            Some(Status { status: OverrideStatus::Isolate, .. }) => break,
                            _ => continue,
                        }
                    }
                    valid_isolate_count -= 1;
                }
                let last = stack.last();
                levels[i] = last.level;
                match last.status {
                    OverrideStatus::RTL => processing_classes[i] = R,
                    OverrideStatus::LTR => processing_classes[i] = L,
                    _ => {}
                }
            }

            // <http://www.unicode.org/reports/tr9/#X7>
            PDF => {
                if overflow_isolate_count > 0 {
                    continue;
                }
                if overflow_embedding_count > 0 {
                    overflow_embedding_count -= 1;
                    continue;
                }
                if stack.last().status != OverrideStatus::Isolate && stack.vec.len() >= 2 {
                    stack.vec.pop();
                }
                // The spec doesn't explicitly mention this step, but it is necessary.
                // See the reference implementations for comparison.
                levels[i] = stack.last().level;
            }

            // Nothing
            B | BN => {}

            // <http://www.unicode.org/reports/tr9/#X6>
            _ => {
                let last = stack.last();
                levels[i] = last.level;
                match last.status {
                    OverrideStatus::RTL => processing_classes[i] = R,
                    OverrideStatus::LTR => processing_classes[i] = L,
                    _ => {}
                }
            }
        }

        // Handle multi-byte characters.
        for j in 1..c.len_utf8() {
            levels[i + j] = levels[i];
            processing_classes[i + j] = processing_classes[i];
        }
    }
}

/// Entries in the directional status stack:
struct Status {
    level: Level,
    status: OverrideStatus,
}

#[derive(PartialEq)]
enum OverrideStatus {
    Neutral,
    RTL,
    LTR,
    Isolate,
}

struct DirectionalStatusStack {
    vec: Vec<Status>,
}

impl DirectionalStatusStack {
    fn new() -> Self {
        DirectionalStatusStack { vec: Vec::with_capacity(Level::max_explicit_depth() as usize + 2) }
    }

    fn push(&mut self, level: Level, status: OverrideStatus) {
        self.vec.push(Status { level, status });
    }

    fn last(&self) -> &Status {
        self.vec.last().unwrap()
    }
}