Codex
64 lines
2.3 KiB
JavaScript
64 lines
2.3 KiB
JavaScript
function assertPowerOfTwo(value) {
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if (!Number.isInteger(value) || value < 2 || (value & (value - 1)) !== 0) {
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throw new Error(`FFT 크기는 2 이상의 2의 거듭제곱이어야 합니다: ${value}`);
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}
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}
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export function fftInPlace(real, imaginary, inverse = false) {
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const size = real.length;
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if (imaginary.length !== size) throw new Error("FFT real/imaginary 길이가 다릅니다.");
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assertPowerOfTwo(size);
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for (let index = 1, reversed = 0; index < size; index += 1) {
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let bit = size >> 1;
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while (reversed & bit) {
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reversed ^= bit;
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bit >>= 1;
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}
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reversed ^= bit;
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if (index < reversed) {
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[real[index], real[reversed]] = [real[reversed], real[index]];
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[imaginary[index], imaginary[reversed]] = [imaginary[reversed], imaginary[index]];
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}
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}
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const direction = inverse ? 1 : -1;
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for (let length = 2; length <= size; length <<= 1) {
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const angle = (direction * 2 * Math.PI) / length;
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const stepReal = Math.cos(angle);
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const stepImaginary = Math.sin(angle);
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for (let start = 0; start < size; start += length) {
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let twiddleReal = 1;
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let twiddleImaginary = 0;
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const halfLength = length >> 1;
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for (let offset = 0; offset < halfLength; offset += 1) {
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const evenIndex = start + offset;
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const oddIndex = evenIndex + halfLength;
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const oddReal = real[oddIndex] * twiddleReal - imaginary[oddIndex] * twiddleImaginary;
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const oddImaginary = real[oddIndex] * twiddleImaginary + imaginary[oddIndex] * twiddleReal;
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real[oddIndex] = real[evenIndex] - oddReal;
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imaginary[oddIndex] = imaginary[evenIndex] - oddImaginary;
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real[evenIndex] += oddReal;
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imaginary[evenIndex] += oddImaginary;
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const nextTwiddleReal = twiddleReal * stepReal - twiddleImaginary * stepImaginary;
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twiddleImaginary = twiddleReal * stepImaginary + twiddleImaginary * stepReal;
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twiddleReal = nextTwiddleReal;
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}
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}
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}
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if (inverse) {
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for (let index = 0; index < size; index += 1) {
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real[index] /= size;
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imaginary[index] /= size;
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}
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}
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}
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export function fftReal(samples) {
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const real = Float64Array.from(samples);
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const imaginary = new Float64Array(real.length);
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fftInPlace(real, imaginary);
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return { real, imaginary };
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}
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