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# N=4

Module by: C. Sidney Burrus. E-mail the author

## N=4 FFT module

A FORTRAN implementation of a length-4 FFT module to be used in a Prime Factor Algorithm program or other FFT program. In Place version.

C
C----------------WFTA N=4---------------------------------
C
104   R1 = A(1) + A(3)
T1 = A(1) - A(3)
R2 = A(2) + A(4)
A(1) = R1 + R2
A(3) = R1 - R2
C
R1 = B(1) + B(3)
T2 = B(1) - B(3)
R2 = B(2) + B(4)
B(1) = R1 + R2
B(3) = R1 - R2
C
R1 = A(2) - A(4)
R2 = B(2) - B(4)
C
A(2) = T1 + R2
A(4) = T1 - R2
B(2) = T2 - R1
B(4) = T2 + R1
C
GOTO 20
C

Figure.  Length-4 FFT Module


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