yetangitu/bitjs
1
0
Fork 0
mirror of https://github.com/codedread/bitjs synced 2025-10-03 17:49:16 +02:00
Code Issues Releases Wiki Activity

Implement crc32 calculation for issue #29

Browse source
This commit is contained in:
Jeff Schiller 2021-12-16 15:09:20 -05:00
parent c0afe7637e
commit 596a859bdc
2 changed files with 46 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

5
archive/unzip.js
View file

@ -220,7 +220,8 @@ class ZipLocalFile {
/**
* Returns a table of Huffman codes. Each entry's key is its code and its value is a JavaScript
* object containing {length: 6, symbol: X}.
* @param {number[]} bitLengths
* @param {number[]} bitLengths An array representing the bit lengths of the codes, in order.
* See section 3.2.2 of https://datatracker.ietf.org/doc/html/rfc1951.
* @returns {Map<number, SymbolLengthPair>}
*/
function getHuffmanCodes(bitLengths) {
@ -267,7 +268,7 @@ function getHuffmanCodes(bitLengths) {
for (let n = 0; n < numLengths; ++n) {
const len = bitLengths[n];
if (len != 0) {
table.set(next_code[len], { length: len, symbol: n }); //, bitstring: binaryValueToString(next_code[len],len) };
table.set(next_code[len], { length: len, symbol: n });
next_code[len]++;
}
}

50
archive/zip.js
View file

@ -47,6 +47,7 @@ importScripts('../io/bytestream-worker.js');
const zLocalFileHeaderSignature = 0x04034b50;
const zCentralFileHeaderSignature = 0x02014b50;
const zEndOfCentralDirSignature = 0x06054b50;
const zCRC32MagicNumber = 0xedb88320; // 0xdebb20e3;
/**
* @typedef CentralDirectoryFileHeaderInfo An object to be used to construct the central directory.
@ -77,9 +78,46 @@ const CompressorState = {
};
let state = CompressorState.NOT_STARTED;
let lastFileReceived = false;
const crc32Table = createCRC32Table();
/** Helper functions. */
/**
* Logic taken from https://github.com/nodeca/pako/blob/master/lib/zlib/crc32.js
* @returns {Uint8Array}
*/
function createCRC32Table() {
const table = new Uint32Array(256);
for (let n = 0; n < 256; n++) {
let c = n;
for (let k = 0; k < 8; k++) {
c = ((c & 1) ? (zCRC32MagicNumber ^ (c >>> 1)) : (c >>> 1));
}
table[n] = c;
}
return table;
};
/**
* Logic taken from https://github.com/nodeca/pako/blob/master/lib/zlib/crc32.js
* @param {number} crc
* @param {Uint8Array} bytes
* @returns {number}
*/
function calculateCRC32(crc, bytes) {
const len = bytes.byteLength;
crc ^= -1;
for (const byte of bytes) {
crc = (crc >>> 8) ^ crc32Table[(crc ^ byte) & 0xFF];
}
crc ^= -1;
if (crc < 0) {
crc += 0x100000000;
}
return crc;
}
/**
* Logic taken from https://github.com/thejoshwolfe/yazl.
* @param {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
@ -129,8 +167,7 @@ function zipOneFile(file) {
compressionMethod: 0,
lastModFileTime: dateToDosTime(jsDate),
lastModFileDate: dateToDosDate(jsDate),
// TODO: Calculate. See section 4.4.7 of https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT.
crc32: 0,
crc32: calculateCRC32(0, file.fileData),
// TODO: For now, this is easy. Later when we do DEFLATE, we will have to calculate.
compressedSize: file.fileData.byteLength,
uncompressedSize: file.fileData.byteLength,
@ -157,10 +194,9 @@ function zipOneFile(file) {
*/
function writeCentralFileDirectory() {
// Each central directory file header is 46 bytes + the filename.
let filenameLengths = filesCompressed.map(f => f.fileName.length).reduce((acc, cur) => acc + cur);
const sizeOfCentralDirectoryEntries = (filesCompressed.length * 46) + filenameLengths;
const buffer = new bitjs.io.ByteBuffer(sizeOfCentralDirectoryEntries + 22);
let cdsLength = filesCompressed.map(f => f.fileName.length + 46).reduce((a, c) => a + c);
// 22 extra bytes for the end-of-central-dir header.
const buffer = new bitjs.io.ByteBuffer(cdsLength + 22);
for (const cdInfo of centralDirectoryInfos) {
buffer.writeNumber(zCentralFileHeaderSignature, 4); // Magic number.
@ -189,7 +225,7 @@ function writeCentralFileDirectory() {
buffer.writeNumber(0, 2); // Disk where central directory starts.
buffer.writeNumber(filesCompressed.length, 2); // Number of central directory records on this disk.
buffer.writeNumber(filesCompressed.length, 2); // Total number of central directory records.
buffer.writeNumber(sizeOfCentralDirectoryEntries, 4); // Size of central directory.
buffer.writeNumber(cdsLength, 4); // Size of central directory.
buffer.writeNumber(numBytesWritten, 4); // Offset of start of central directory.
buffer.writeNumber(0, 2); // Comment length.