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bitrevorder - Permute data into bit-reversed order

Syntax

y = bitrevorder(x)
[y,i] = bitrevorder(x)

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

fft, digitrevorder, ifft

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