62 lines
1.8 KiB
JavaScript
62 lines
1.8 KiB
JavaScript
var bodec = require('bodec');
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module.exports = applyDelta;
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function applyDelta(delta, base) {
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var deltaOffset = 0;
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if (base.length !== readLength()) {
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throw new Error("Base length mismatch");
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}
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// Create a new output buffer with length from header.
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var outOffset = 0;
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var out = bodec.create(readLength());
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while (deltaOffset < delta.length) {
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var byte = delta[deltaOffset++];
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// Copy command. Tells us offset in base and length to copy.
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if (byte & 0x80) {
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var offset = 0;
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var length = 0;
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if (byte & 0x01) offset |= delta[deltaOffset++] << 0;
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if (byte & 0x02) offset |= delta[deltaOffset++] << 8;
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if (byte & 0x04) offset |= delta[deltaOffset++] << 16;
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if (byte & 0x08) offset |= delta[deltaOffset++] << 24;
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if (byte & 0x10) length |= delta[deltaOffset++] << 0;
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if (byte & 0x20) length |= delta[deltaOffset++] << 8;
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if (byte & 0x40) length |= delta[deltaOffset++] << 16;
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if (length === 0) length = 0x10000;
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// copy the data
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bodec.copy(bodec.slice(base, offset, offset + length), out, outOffset);
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outOffset += length;
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}
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// Insert command, opcode byte is length itself
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else if (byte) {
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bodec.copy(bodec.slice(delta, deltaOffset, deltaOffset + byte), out, outOffset);
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deltaOffset += byte;
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outOffset += byte;
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}
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else throw new Error('Invalid delta opcode');
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}
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if (outOffset !== out.length) {
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throw new Error("Size mismatch in check");
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}
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return out;
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// Read a variable length number our of delta and move the offset.
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function readLength() {
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var byte = delta[deltaOffset++];
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var length = byte & 0x7f;
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var shift = 7;
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while (byte & 0x80) {
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byte = delta[deltaOffset++];
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length |= (byte & 0x7f) << shift;
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shift += 7;
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}
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return length;
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}
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}
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