1 files changed, 152 insertions, 15 deletions
diff --git a/tools/editor/dct.js b/tools/editor/dct.js
index e48ce2b..c081473 100644
--- a/tools/editor/dct.js
+++ b/tools/editor/dct.js
@@ -1,21 +1,6 @@
 const dctSize = 512; // Default DCT size, read from header
 
 // --- Utility Functions for Audio Processing ---
-// JavaScript equivalent of C++ idct_512
-function javascript_idct_512(input) {
-    const output = new Float32Array(dctSize);
-    const PI = Math.PI;
-    const N = dctSize;
-
-    for (let n = 0; n < N; ++n) {
-        let sum = input[0] / 2.0;
-        for (let k = 1; k < N; ++k) {
-            sum += input[k] * Math.cos((PI / N) * k * (n + 0.5));
-        }
-        output[n] = sum * (2.0 / N);
-    }
-    return output;
-}
 
 // Hanning window for smooth audio transitions (JavaScript equivalent)
 function hanningWindow(size) {
@@ -29,3 +14,155 @@ function hanningWindow(size) {
 
 const hanningWindowArray = hanningWindow(dctSize); // Pre-calculate window
 
+// ============================================================================
+// FFT-based DCT/IDCT Implementation
+// ============================================================================
+
+// Bit-reversal permutation (in-place)
+function bitReversePermute(real, imag, N) {
+    let temp_bits = N;
+    let num_bits = 0;
+    while (temp_bits > 1) {
+        temp_bits >>= 1;
+        num_bits++;
+    }
+
+    for (let i = 0; i < N; i++) {
+        let j = 0;
+        let temp = i;
+        for (let b = 0; b < num_bits; b++) {
+            j = (j << 1) | (temp & 1);
+            temp >>= 1;
+        }
+
+        if (j > i) {
+            const tmp_real = real[i];
+            const tmp_imag = imag[i];
+            real[i] = real[j];
+            imag[i] = imag[j];
+            real[j] = tmp_real;
+            imag[j] = tmp_imag;
+        }
+    }
+}
+
+// In-place radix-2 FFT
+function fftRadix2(real, imag, N, direction) {
+    const PI = Math.PI;
+
+    for (let stage_size = 2; stage_size <= N; stage_size *= 2) {
+        const half_stage = stage_size / 2;
+        const angle = direction * 2.0 * PI / stage_size;
+
+        let wr = 1.0;
+        let wi = 0.0;
+        const wr_delta = Math.cos(angle);
+        const wi_delta = Math.sin(angle);
+
+        for (let k = 0; k < half_stage; k++) {
+            for (let group_start = k; group_start < N; group_start += stage_size) {
+                const i = group_start;
+                const j = group_start + half_stage;
+
+                const temp_real = real[j] * wr - imag[j] * wi;
+                const temp_imag = real[j] * wi + imag[j] * wr;
+
+                real[j] = real[i] - temp_real;
+                imag[j] = imag[i] - temp_imag;
+                real[i] = real[i] + temp_real;
+                imag[i] = imag[i] + temp_imag;
+            }
+
+            const wr_old = wr;
+            wr = wr_old * wr_delta - wi * wi_delta;
+            wi = wr_old * wi_delta + wi * wr_delta;
+        }
+    }
+}
+
+function fftForward(real, imag, N) {
+    bitReversePermute(real, imag, N);
+    fftRadix2(real, imag, N, +1);
+}
+
+function fftInverse(real, imag, N) {
+    bitReversePermute(real, imag, N);
+    fftRadix2(real, imag, N, -1);
+
+    const scale = 1.0 / N;
+    for (let i = 0; i < N; i++) {
+        real[i] *= scale;
+        imag[i] *= scale;
+    }
+}
+
+// DCT-II via FFT using reordering method
+function javascript_dct_fft(input, N) {
+    const PI = Math.PI;
+
+    const real = new Float32Array(N);
+    const imag = new Float32Array(N);
+
+    for (let i = 0; i < N / 2; i++) {
+        real[i] = input[2 * i];
+        real[N - 1 - i] = input[2 * i + 1];
+    }
+
+    fftForward(real, imag, N);
+
+    const output = new Float32Array(N);
+    for (let k = 0; k < N; k++) {
+        const angle = -PI * k / (2.0 * N);
+        const wr = Math.cos(angle);
+        const wi = Math.sin(angle);
+
+        const dct_value = real[k] * wr - imag[k] * wi;
+
+        if (k === 0) {
+            output[k] = dct_value * Math.sqrt(1.0 / N);
+        } else {
+            output[k] = dct_value * Math.sqrt(2.0 / N);
+        }
+    }
+
+    return output;
+}
+
+// IDCT (DCT-III) via FFT using reordering method
+function javascript_idct_fft(input, N) {
+    const PI = Math.PI;
+
+    const real = new Float32Array(N);
+    const imag = new Float32Array(N);
+
+    for (let k = 0; k < N; k++) {
+        const angle = PI * k / (2.0 * N);
+        const wr = Math.cos(angle);
+        const wi = Math.sin(angle);
+
+        let scaled;
+        if (k === 0) {
+            scaled = input[k] / Math.sqrt(1.0 / N);
+        } else {
+            scaled = input[k] / Math.sqrt(2.0 / N) * 2.0;
+        }
+
+        real[k] = scaled * wr;
+        imag[k] = scaled * wi;
+    }
+
+    fftInverse(real, imag, N);
+
+    const output = new Float32Array(N);
+    for (let i = 0; i < N / 2; i++) {
+        output[2 * i] = real[i];
+        output[2 * i + 1] = real[N - 1 - i];
+    }
+
+    return output;
+}
+
+// Fast O(N log N) IDCT using FFT
+function javascript_idct_512(input) {
+    return javascript_idct_fft(input, dctSize);
+}