Package org.apfloat.internal

Class Scramble

java.lang.Object

org.apfloat.internal.Scramble

public class Scramble
extends Object

Functions to perform bit-reverse ordering of data.

Version:

1.0

Author:

Mikko Tommila

Method Summary

Modifier and Type	Method	Description
static int[]	createScrambleTable(int length)	Create a table of indexes for scrambling an array for FFT.
static int	permute(int n, int length)	Permute the bits of a number to reverse order.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

permute

public static int permute(int n,
 int length)

Permute the bits of a number to reverse order.

For example, if n is 5 and the transform length is 256, the permutation is (in binary)

00000101 → 10100000

Parameters:

n - The number whose bits to reverse.

length - The FFT transform length for which the bit reversal to perform.

Returns:

The bits of n reversed.

createScrambleTable

public static int[] createScrambleTable(int length)

Create a table of indexes for scrambling an array for FFT.

The returned table contains pairs of indexes that should be swapped to scramble an array. For example, for transform length 8 the returned table contains { 1, 4, 3, 6 } to indicate that the array elements [1] and [4] should be swapped, and the elements [3] and [6] should be swapped.

Parameters:

length - The FFT transform length for which the scrambling table is created.

Returns:

An array of pairs of indexes that indicate, which array elements should be swapped to scramble the array.