bitrevorder - Permute data into bit-reversed order

Syntax

Description

bitrevorder is useful for pre-arranging filter coefficients so that bit-reversed ordering does not have to be performed as part of an fft or inverse FFT (ifft) computation. This can improve run-time efficiency for external applications or for Simulink^® blockset models. Both MATLAB fft and ifft functions process linear input and output.

Note   Using bitrevorder is equivalent to using digitrevorder with radix base 2.

y = bitrevorder(x) returns the input data in bit-reversed order in vector or matrix y. The length of x must be an integer power of 2. If x is a matrix, the bit-reversal occurs on the first dimension of x with size greater than 1. y is the same size as x.

[y,i] = bitrevorder(x) returns the bit-reversed vector or matrix y and the bit-reversed indices i, such that y = x(i). Recall that MATLAB matrices use 1-based indexing, so the first index of y will be 1, not 0.

The following table shows the numbers 0 through 7, the corresponding bits and the bit-reversed numbers.

Linear Index	Bits	Bit- Reversed	Bit-Reversed Index
0	000	000	0
1	001	100	4
2	010	010	2
3	011	110	6
4	100	001	1
5	101	101	5
6	110	011	3
7	111	111	7

Examples

Obtain the bit-reversed ordered output of a vector:

x=[0:7]';                % Create a column vector
[x,bitrevorder(x)]
%	ans =
%     0     0
%     1     4
%     2     2
%     3     6
%     4     1
%     5     5
%     6     3
%     7     7

See Also

digitrevorder | fft | ifft

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