js-cfb/bits/81_inflate.js

/* modified inflate function also moves original read head */

var dyn_lmap = use_typed_arrays ? new Uint16Array(32768) : zero_fill_array(32768);
var dyn_dmap = use_typed_arrays ? new Uint16Array(32768) : zero_fill_array(32768);
var dyn_cmap = use_typed_arrays ? new Uint16Array(128)   : zero_fill_array(128);
var dyn_len_1 = 1, dyn_len_2 = 1;

/* 5.5.3 Expanding Huffman Codes */
function dyn(data, boff/*:number*/) {
	/* nomenclature from RFC1951 refers to bit values; these are offset by the implicit constant */
	var _HLIT = read_bits_5(data, boff) + 257; boff += 5;
	var _HDIST = read_bits_5(data, boff) + 1; boff += 5;
	var _HCLEN = read_bits_4(data, boff) + 4; boff += 4;
	var w = 0;

	/* grab and store code lengths */
	var clens = use_typed_arrays ? new Uint8Array(19) : zero_fill_array(19);
	var ctree = [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ];
	var maxlen = 1;
	var bl_count =  use_typed_arrays ? new Uint8Array(8) : zero_fill_array(8);
	var next_code = use_typed_arrays ? new Uint8Array(8) : zero_fill_array(8);
	var L = clens.length; /* 19 */
	for(var i = 0; i < _HCLEN; ++i) {
		clens[CLEN_ORDER[i]] = w = read_bits_3(data, boff);
		if(maxlen < w) maxlen = w;
		bl_count[w]++;
		boff += 3;
	}

	/* build code tree */
	var ccode = 0;
	bl_count[0] = 0;
	for(i = 1; i <= maxlen; ++i) next_code[i] = ccode = (ccode + bl_count[i-1])<<1;
	for(i = 0; i < L; ++i) if((ccode = clens[i]) != 0) ctree[i] = next_code[ccode]++;
	/* cmap[7 bits from stream] = (off&7) + (lit<<3) */
	var cleni = 0;
	for(i = 0; i < L; ++i) {
		cleni = clens[i];
		if(cleni != 0) {
			ccode = bitswap8[ctree[i]]>>(8-cleni);
			for(var j = (1<<(7-cleni))-1; j>=0; --j) dyn_cmap[ccode|(j<<cleni)] = (cleni&7) | (i<<3);
		}
	}

	/* read literal and dist codes at once */
	var hcodes/*:Array<number>*/ = [];
	maxlen = 1;
	for(; hcodes.length < _HLIT + _HDIST;) {
		ccode = dyn_cmap[read_bits_7(data, boff)];
		boff += ccode & 7;
		switch((ccode >>>= 3)) {
			case 16:
				w = 3 + read_bits_2(data, boff); boff += 2;
				ccode = hcodes[hcodes.length - 1];
				while(w-- > 0) hcodes.push(ccode);
				break;
			case 17:
				w = 3 + read_bits_3(data, boff); boff += 3;
				while(w-- > 0) hcodes.push(0);
				break;
			case 18:
				w = 11 + read_bits_7(data, boff); boff += 7;
				while(w -- > 0) hcodes.push(0);
				break;
			default:
				hcodes.push(ccode);
				if(maxlen < ccode) maxlen = ccode;
				break;
		}
	}

	/* build literal / length trees */
	var h1 = hcodes.slice(0, _HLIT), h2 = hcodes.slice(_HLIT);
	for(i = _HLIT; i < 286; ++i) h1[i] = 0;
	for(i = _HDIST; i < 30; ++i) h2[i] = 0;
	dyn_len_1 = build_tree(h1, dyn_lmap, 286);
	dyn_len_2 = build_tree(h2, dyn_dmap, 30);
	return boff;
}

/* return [ data, bytesRead ] */
function inflate(data, usz/*:number*/) {
	/* shortcircuit for empty buffer [0x03, 0x00] */
	if(data[0] == 3 && !(data[1] & 0x3)) { return [new_raw_buf(usz), 2]; }

	/* bit offset */
	var boff = 0;

	/* header includes final bit and type bits */
	var header = 0;

	var outbuf = new_unsafe_buf(usz ? usz : (1<<18));
	var woff = 0;
	var OL = outbuf.length>>>0;
	var max_len_1 = 0, max_len_2 = 0;

	while((header&1) == 0) {
		header = read_bits_3(data, boff); boff += 3;
		if((header >>> 1) == 0) {
			/* Stored block */
			if(boff & 7) boff += 8 - (boff&7);
			/* 2 bytes sz, 2 bytes bit inverse */
			var sz = data[boff>>>3] | data[(boff>>>3)+1]<<8;
			boff += 32;
			/* push sz bytes */
			if(sz > 0) {
				if(!usz && OL < woff + sz) { outbuf = realloc(outbuf, woff + sz); OL = outbuf.length; }
				while(sz-- > 0) { outbuf[woff++] = data[boff>>>3]; boff += 8; }
			}
			continue;
		} else if((header >> 1) == 1) {
			/* Fixed Huffman */
			max_len_1 = 9; max_len_2 = 5;
		} else {
			/* Dynamic Huffman */
			boff = dyn(data, boff);
			max_len_1 = dyn_len_1; max_len_2 = dyn_len_2;
		}
		for(;;) { // while(true) is apparently out of vogue in modern JS circles
			if(!usz && (OL < woff + 32767)) { outbuf = realloc(outbuf, woff + 32767); OL = outbuf.length; }
			/* ingest code and move read head */
			var bits = read_bits_n(data, boff, max_len_1);
			var code = (header>>>1) == 1 ? fix_lmap[bits] : dyn_lmap[bits];
			boff += code & 15; code >>>= 4;
			/* 0-255 are literals, 256 is end of block token, 257+ are copy tokens */
			if(((code>>>8)&0xFF) === 0) outbuf[woff++] = code;
			else if(code == 256) break;
			else {
				code -= 257;
				var len_eb = (code < 8) ? 0 : ((code-4)>>2); if(len_eb > 5) len_eb = 0;
				var tgt = woff + LEN_LN[code];
				/* length extra bits */
				if(len_eb > 0) {
					tgt += read_bits_n(data, boff, len_eb);
					boff += len_eb;
				}

				/* dist code */
				bits = read_bits_n(data, boff, max_len_2);
				code = (header>>>1) == 1 ? fix_dmap[bits] : dyn_dmap[bits];
				boff += code & 15; code >>>= 4;
				var dst_eb = (code < 4 ? 0 : (code-2)>>1);
				var dst = DST_LN[code];
				/* dist extra bits */
				if(dst_eb > 0) {
					dst += read_bits_n(data, boff, dst_eb);
					boff += dst_eb;
				}

				/* in the common case, manual byte copy is faster than TA set / Buffer copy */
				if(!usz && OL < tgt) { outbuf = realloc(outbuf, tgt + 100); OL = outbuf.length; }
				while(woff < tgt) { outbuf[woff] = outbuf[woff - dst]; ++woff; }
			}
		}
	}
	if(usz) return [outbuf, (boff+7)>>>3];
	return [outbuf.slice(0, woff), (boff+7)>>>3];
}

function _inflate(payload, usz) {
	var data = payload.slice(payload.l||0);
	var out = inflate(data, usz);
	payload.l += out[1];
	return out[0];
}