changeset 24:e705de983b67

Put the comments back in!

--- a/fft/nayuki-obj/fft.js	Tue Oct 06 17:51:43 2015 +0100
+++ b/fft/nayuki-obj/fft.js	Wed Oct 07 08:57:11 2015 +0100
@@ -3,7 +3,7 @@
  * 
  * Copyright (c) 2014 Project Nayuki
  * http://www.nayuki.io/page/free-small-fft-in-multiple-languages
- * 
+ *
  * (MIT License)
  * Permission is hereby granted, free of charge, to any person obtaining a copy of
  * this software and associated documentation files (the "Software"), to deal in
@@ -20,10 +20,15 @@
  *   liability, whether in an action of contract, tort or otherwise, arising from,
  *   out of or in connection with the Software or the use or other dealings in the
  *   Software.
+ *
+ * Slightly restructured by Chris Cannam, [e-mail]
  */
 
 "use strict";
 
+/* 
+ * Construct an object for calculating the discrete Fourier transform (DFT) of size n, where n is a power of 2.
+ */
 function FFTNayuki(n) {
     
     this.n = n;
@@ -45,10 +50,15 @@
         this.sinTable[i] = Math.sin(2 * Math.PI * i / n);
     }
 
+    /* 
+     * Computes the discrete Fourier transform (DFT) of the given complex vector, storing the result back into the vector.
+     * The vector's length must be equal to the size n that was passed to the object constructor, and this must be a power of 2. Uses the Cooley-Tukey decimation-in-time radix-2 algorithm.
+     */
     this.forward = function(real, imag) {
 
 	var n = this.n;
 	
+	// Bit-reversed addressing permutation
 	for (var i = 0; i < n; i++) {
             var j = reverseBits(i, this.levels);
             if (j > i) {
@@ -61,6 +71,7 @@
             }
 	}
     
+	// Cooley-Tukey decimation-in-time radix-2 FFT
 	for (var size = 2; size <= n; size *= 2) {
             var halfsize = size / 2;
             var tablestep = n / size;
@@ -78,6 +89,7 @@
             }
 	}
     
+	// Returns the integer whose value is the reverse of the lowest 'bits' bits of the integer 'x'.
 	function reverseBits(x, bits) {
             var y = 0;
             for (var i = 0; i < bits; i++) {
@@ -88,6 +100,10 @@
 	}
     }
 
+    /* 
+     * Computes the inverse discrete Fourier transform (IDFT) of the given complex vector, storing the result back into the vector.
+     * The vector's length must be equal to the size n that was passed to the object constructor, and this must be a power of 2. This is a wrapper function. This transform does not perform scaling, so the inverse is not a true inverse.
+     */
     this.inverse = function(real, imag) {
 	forward(imag, real);
     }