dropflow/dist/src/string-trie.js

A small CSS2 document renderer built from specifications

// This originally came from fb55/entities by Felix Böhm:
//
// scripts/trie/trie.ts
// scripts/trie/encode-trie.ts
//
// Copyright (c) Felix Böhm
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
//
// Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// THIS IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
export var BinTrieFlags;
(function (BinTrieFlags) {
    BinTrieFlags[BinTrieFlags["VALUE_LENGTH"] = 49152] = "VALUE_LENGTH";
    BinTrieFlags[BinTrieFlags["BRANCH_LENGTH"] = 16256] = "BRANCH_LENGTH";
    BinTrieFlags[BinTrieFlags["JUMP_TABLE"] = 127] = "JUMP_TABLE";
})(BinTrieFlags || (BinTrieFlags = {}));
/**
 * Determines the branch of the current node that is taken given the current
 * character. This function is used to traverse the trie.
 *
 * @param decodeTree The trie.
 * @param current The current node.
 * @param nodeIdx The index right after the current node and its value.
 * @param char The current character.
 * @returns The index of the next node, or -1 if no branch is taken.
 */
export function determineBranch(decodeTree, current, nodeIdx, char) {
    const branchCount = (current & BinTrieFlags.BRANCH_LENGTH) >> 7;
    const jumpOffset = current & BinTrieFlags.JUMP_TABLE;
    // Case 1: Single branch encoded in jump offset
    if (branchCount === 0) {
        return jumpOffset !== 0 && char === jumpOffset ? nodeIdx : -1;
    }
    // Case 2: Multiple branches encoded in jump table
    if (jumpOffset) {
        const value = char - jumpOffset;
        return value < 0 || value >= branchCount
            ? -1
            : decodeTree[nodeIdx + value] - 1;
    }
    // Case 3: Multiple branches encoded in dictionary
    // Binary search for the character.
    let lo = nodeIdx;
    let hi = lo + branchCount - 1;
    while (lo <= hi) {
        const mid = (lo + hi) >>> 1;
        const midVal = decodeTree[mid];
        if (midVal < char) {
            lo = mid + 1;
        }
        else if (midVal > char) {
            hi = mid - 1;
        }
        else {
            return decodeTree[mid + branchCount];
        }
    }
    return -1;
}