SoundPlayer: Implement the Fast Fourier Transform algorithm

2 files changed, 110 insertions, 0 deletions

diff --git a/Userland/Applications/SoundPlayer/AudioAlgorithms.cpp b/Userland/Applications/SoundPlayer/AudioAlgorithms.cpp
new file mode 100644
index 0000000000..f1420c27cd
--- /dev/null
+++ b/Userland/Applications/SoundPlayer/AudioAlgorithms.cpp
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2021, Cesar Torres <shortanemoia@protonmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "AudioAlgorithms.h"
+#include <AK/Complex.h>
+#include <math.h>
+
+// This function uses the input vector as output too. therefore, if you wish to
+// leave it intact, pass a copy to this function
+//
+// The sampling frequency must be more than twice the frequency to resolve.
+// The sample window must be at least large enough to reflect the periodicity
+// of the smallest frequency to be resolved.
+//
+// For example, to resolve a 10 KHz and a 2 Hz sine waves we need at least
+// a samplerate of 20 KHz and a window of 0.5 seconds
+//
+// If invert is true, this function computes the inverse discrete fourier transform.
+//
+// The data vector must be a power of 2
+// Adapted from https://cp-algorithms.com/algebra/fft.html
+void fft(Vector<Complex<double>>& sample_data, bool invert)
+{
+    int n = sample_data.size();
+    auto data = sample_data.data();
+
+    for (int i = 1, j = 0; i < n; i++) {
+        int bit = n >> 1;
+        for (; j & bit; bit >>= 1)
+            j ^= bit;
+        j ^= bit;
+
+        if (i < j)
+            swap(data[i], data[j]);
+    }
+
+    for (int len = 2; len <= n; len <<= 1) {
+        double ang = 2 * M_PI / len * (invert ? -1 : 1);
+        Complex<double> wlen(cos(ang), sin(ang));
+        for (int i = 0; i < n; i += len) {
+            Complex<double> w = { 1., 0. };
+            for (int j = 0; j < len / 2; j++) {
+                Complex<double> u = data[i + j], v = data[i + j + len / 2] * w;
+                data[i + j] = u + v;
+                data[i + j + len / 2] = u - v;
+                w *= wlen;
+            }
+        }
+    }
+
+    if (invert) {
+        for (int i = 0; i < n; i++)
+            data[i] /= n;
+    }
+}
diff --git a/Userland/Applications/SoundPlayer/AudioAlgorithms.h b/Userland/Applications/SoundPlayer/AudioAlgorithms.h
new file mode 100644
index 0000000000..606d4eb833
--- /dev/null
+++ b/Userland/Applications/SoundPlayer/AudioAlgorithms.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2021, Cesar Torres <shortanemoia@protonmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Complex.h>
+#include <AK/Vector.h>
+
+void fft(Vector<Complex<double>>& sample_data, bool invert);