35 lines
1.2 KiB
JavaScript
35 lines
1.2 KiB
JavaScript
const crcTable = [];
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for (let n = 0; n < 256; n++) {
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let c = n;
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for (let k = 0; k < 8; k++) {
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if (c & 1) {
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c = 0xedb88320 ^ (c >>> 1);
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}
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else {
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c = c >>> 1;
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}
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}
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crcTable[n] = c;
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}
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const initialCrc = 0xffffffff;
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function updateCrc(currentCrc, data, length) {
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let c = currentCrc;
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for (let n = 0; n < length; n++) {
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c = crcTable[(c ^ data[n]) & 0xff] ^ (c >>> 8);
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}
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return c;
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}
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function crc(data, length) {
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return (updateCrc(initialCrc, data, length) ^ initialCrc) >>> 0;
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}
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export function checkCrc(buffer, crcLength, chunkName) {
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const expectedCrc = buffer.readUint32();
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const actualCrc = crc(new Uint8Array(buffer.buffer, buffer.byteOffset + buffer.offset - crcLength - 4, crcLength), crcLength); // "- 4" because we already advanced by reading the CRC
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if (actualCrc !== expectedCrc) {
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throw new Error(`CRC mismatch for chunk ${chunkName}. Expected ${expectedCrc}, found ${actualCrc}`);
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}
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}
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export function writeCrc(buffer, length) {
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buffer.writeUint32(crc(new Uint8Array(buffer.buffer, buffer.byteOffset + buffer.offset - length, length), length));
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}
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//# sourceMappingURL=crc.js.map
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