52 lines
2.2 KiB
TypeScript
52 lines
2.2 KiB
TypeScript
/* eslint-disable no-bitwise */
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// eslint-disable-next-line max-len
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// Ref: https://github.com/telegramdesktop/tdesktop/blob/0743e71ab6b928d2ee5bae1aed991849b1e2b291/Telegram/SourceFiles/data/data_document.cpp#L1018
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export function decodeWaveform(encoded5bit: Uint8Array) {
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const bitsCount = encoded5bit.length * 8;
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const valuesCount = Math.floor(bitsCount / 5);
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if (!valuesCount) {
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return [];
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}
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// Read each 5 bit of encoded5bit as 0-31 unsigned char.
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// We count the index of the byte in which the desired 5-bit sequence starts.
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// And then we read a uint16 starting from that byte to guarantee to get all of those 5 bits.
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//
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// BUT! if it is the last byte we have, we're not allowed to read a uint16 starting with it.
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// Because it will be an overflow (we'll access one byte after the available memory).
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// We see, that only the last 5 bits could start in the last available byte and be problematic.
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// So we read in a general way all the entries in a general way except the last one.
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const result = Array(valuesCount);
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const bitsData = encoded5bit;
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for (let i = 0, l = valuesCount - 1; i !== l; ++i) {
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const byteIndex = Math.floor((i * 5) / 8);
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const bitShift = Math.floor((i * 5) % 8);
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const value = bitsData[byteIndex] + (bitsData[byteIndex + 1] << 8);
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result[i] = ((value >> bitShift) & 0x1F);
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}
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const lastByteIndex = Math.floor(((valuesCount - 1) * 5) / 8);
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const lastBitShift = Math.floor(((valuesCount - 1) * 5) % 8);
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const lastValue = bitsData[lastByteIndex] + (bitsData[lastByteIndex + 1] << 8);
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result[valuesCount - 1] = (lastValue >> lastBitShift) & 0x1F;
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return result;
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}
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export function interpolateArray(data: number[], fitCount: number) {
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let peak = 0;
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const newData = new Array(fitCount);
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const springFactor = data.length / fitCount;
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const leftFiller = data[0];
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const rightFiller = data[data.length - 1];
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for (let i = 0; i < fitCount; i++) {
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const idx = Math.floor(i * springFactor);
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const val = ((data[idx - 1] ?? leftFiller) + (data[idx] ?? leftFiller) + (data[idx + 1] ?? rightFiller)) / 3;
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newData[i] = val;
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if (peak < val) {
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peak = val;
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}
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}
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return { data: newData, peak };
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}
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