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Use JS Map instead of JS object for the huffman code tables. Seems to be a pretty good performance improvement on Chrome, Safari, Firefox.

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This commit is contained in:
Jeff Schiller 2021-12-12 00:32:28 -08:00
parent 4496948aaf
commit 843caf4e61
3 changed files with 63 additions and 9 deletions
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15
archive/unzip.js
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@ -251,17 +251,14 @@ function getHuffmanCodes(bitLengths) {
}
// Step 3: Assign numerical values to all codes
const table = {};
let tableLength = 0;
const table = new Map();
for (let n = 0; n < numLengths; ++n) {
const len = bitLengths[n];
if (len != 0) {
table[next_code[len]] = { length: len, symbol: n }; //, bitstring: binaryValueToString(next_code[len],len) };
tableLength++;
table.set(next_code[len], { length: len, symbol: n }); //, bitstring: binaryValueToString(next_code[len],len) };
next_code[len]++;
}
}
table.maxLength = tableLength;
return table;
}
@ -317,7 +314,6 @@ function getFixedDistanceTable() {
function decodeSymbol(bstream, hcTable) {
let code = 0;
let len = 0;
let match = false;
// loop until we match
for (; ;) {
@ -327,16 +323,16 @@ function decodeSymbol(bstream, hcTable) {
++len;
// check against Huffman Code table and break if found
if (hcTable.hasOwnProperty(code) && hcTable[code].length == len) {
if (hcTable.has(code) && hcTable.get(code).length == len) {
break;
}
if (len > hcTable.maxLength) {
err(`Bit stream out of sync, didn't find a Huffman Code, length was ${len} ` +
`and table only max code length of ${hcTable.maxLength}`);
`and table only max code length of ${hcTable.length}`);
break;
}
}
return hcTable[code].symbol;
return hcTable.get(code).symbol;
}
@ -710,6 +706,7 @@ onmessage = function (event) {
bytestream = new bitjs.io.ByteStream(bytes);
} else {
bytestream.push(bytes);
// TODO: Shouldn't this return here if it's not waiting?
}
if (unarchiveState === UnarchiveState.NOT_STARTED) {