Huffman.hx

/*
 * Copyright (C)2005-2019 Haxe Foundation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

package haxe.zip;

enum Huffman {
	Found(i:Int);
	NeedBit(left:Huffman, right:Huffman);
	NeedBits(n:Int, table:Array<Huffman>);
}

class HuffTools {
	public function new() {}

	function treeDepth(t) {
		return switch (t) {
			case Found(_): 0;
			case NeedBits(_, _): throw "assert";
			case NeedBit(a, b):
				var da = treeDepth(a);
				var db = treeDepth(b);
				1 + ((da < db) ? da : db);
		}
	}

	function treeCompress(t) {
		var d = treeDepth(t);
		if (d == 0)
			return t;
		if (d == 1)
			return switch (t) {
				case NeedBit(a, b): NeedBit(treeCompress(a), treeCompress(b));
				default: throw "assert";
			}
		var size = 1 << d;
		var table = new Array();
		for (i in 0...size)
			table.push(Found(-1));
		treeWalk(table, 0, 0, d, t);
		return NeedBits(d, table);
	}

	function treeWalk(table, p, cd, d, t) {
		switch (t) {
			case NeedBit(a, b):
				if (d > 0) {
					treeWalk(table, p, cd + 1, d - 1, a);
					treeWalk(table, p | (1 << cd), cd + 1, d - 1, b);
				} else
					table[p] = treeCompress(t);
			default:
				table[p] = treeCompress(t);
		}
	}

	function treeMake(bits:haxe.ds.IntMap<Int>, maxbits:Int, v:Int, len:Int) {
		if (len > maxbits)
			throw "Invalid huffman";
		var idx = (v << 5) | len;
		if (bits.exists(idx))
			return Found(bits.get(idx));
		v <<= 1;
		len += 1;
		return NeedBit(treeMake(bits, maxbits, v, len), treeMake(bits, maxbits, v | 1, len));
	}

	public function make(lengths, pos, nlengths, maxbits) {
		if (nlengths == 1) {
			return NeedBit(Found(0), Found(0));
		}
		var counts = new Array();
		var tmp = new Array();
		if (maxbits > 32)
			throw "Invalid huffman";
		for (i in 0...maxbits) {
			counts.push(0);
			tmp.push(0);
		}
		for (i in 0...nlengths) {
			var p = lengths[i + pos];
			if (p >= maxbits)
				throw "Invalid huffman";
			counts[p]++;
		}
		var code = 0;
		for (i in 1...maxbits - 1) {
			code = (code + counts[i]) << 1;
			tmp[i] = code;
		}
		var bits = new haxe.ds.IntMap();
		for (i in 0...nlengths) {
			var l = lengths[i + pos];
			if (l != 0) {
				var n = tmp[l - 1];
				tmp[l - 1] = n + 1;
				bits.set((n << 5) | l, i);
			}
		}
		return treeCompress(NeedBit(treeMake(bits, maxbits, 0, 1), treeMake(bits, maxbits, 1, 1)));
	}
}