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# N=7

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

## N=7 FFT module

A FORTRAN implementation of a length-7 FFT module to be used in a Prime Factor Algorithm program or other FFT program. In Place version.

C
DATA  C71, C72  / -1.16666667,-0.79015647 /
DATA  C73, C74  /  0.055854267, 0.7343022 /
DATA  C75, C76  /  0.44095855,-0.34087293 /
DATA  C77, C78  /  0.53396936, 0.87484229 /
C
C-----------------WFTA N=7--------------------------
C
107 R1 = A(2) + A(7)
R6 = A(2) - A(7)
S1 = B(2) + B(7)
S6 = B(2) - B(7)
R2 = A(3) + A(6)
R5 = A(3) - A(6)
S2 = B(3) + B(6)
S5 = B(3) - B(6)
R3 = A(4) + A(5)
R4 = A(4) - A(5)
S3 = B(4) + B(5)
S4 = B(4) - B(5)
C
T3 = (R1 - R2) * C74
T  = (R1 - R3) * C72
R1 = R1 + R2 + R3
A(1) = A(1) + R1
R1   = A(1) + R1 * C71
R2 =(R3 - R2) * C73
R3 = R1 - T + R2
R2 = R1 - R2 - T3
R1 = R1 + T + T3
T = (R6 - R5) * C78
T3 =(R6 + R4) * C76
R6 =(R6 + R5 - R4) * C75
R5 =(R5 + R4) * C77
R4 = R6 - T3 + R5
R5 = R6 - R5 - T
R6 = R6 + T3 + T
C
T3 = (S1 - S2) * C74
T  = (S1 - S3) * C72
S1 =  S1 + S2 + S3
B(1) = B(1) + S1
S1   = B(1) + S1 * C71
S2 =(S3 - S2) * C73
S3 = S1 - T  + S2
S2 = S1 - S2 - T3
S1 = S1 + T  + T3
T  = (S6 - S5) * C78
T3 = (S6 + S4) * C76
S6 = (S6 + S5 - S4) * C75
S5 = (S5 + S4) * C77
S4 = S6 - T3 + S5
S5 = S6 - S5 - T
S6 = S6 + T3 + T
C
A(2) = R3 + S4
A(7) = R3 - S4
A(3) = R1 + S6
A(6) = R1 - S6
A(4) = R2 - S5
A(5) = R2 + S5
B(4) = S2 + R5
B(5) = S2 - R5
B(2) = S3 - R4
B(7) = S3 + R4
B(3) = S1 - R6
B(6) = S1 + R6
C

Figure.  Length-7 FFT Module


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