1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
|
c
c-----------------------------------------------------------------------
c subroutine: fast
c replaces the real vector b(k), for k=1,2,...,n,
c with its finite discrete fourier transform
c-----------------------------------------------------------------------
c
subroutine fast(b, n)
c
c the dc term is returned in location b(1) with b(2) set to 0.
c thereafter the jth harmonic is returned as a complex
c number stored as b(2*j+1) + i b(2*j+2).
c the n/2 harmonic is returned in b(n+1) with b(n+2) set to 0.
c hence, b must be dimensioned to size n+2.
c the subroutine is called as fast(b,n) where n=2**m and
c b is the real array described above.
c
dimension b(2)
common /cons/ pii, p7, p7two, c22, s22, pi2
c
c iw is a machine dependent write device number
c
iw = i1mach(2)
c
pii = 4.*atan(1.)
pi8 = pii/8.
p7 = 1./sqrt(2.)
p7two = 2.*p7
c22 = cos(pi8)
s22 = sin(pi8)
pi2 = 2.*pii
do 10 i=1,15
m = i
nt = 2**i
if (n.eq.nt) go to 20
10 continue
write (iw,9999)
9999 format (33h n is not a power of two for fast)
stop
20 n4pow = m/2
c
c do a radix 2 iteration first if one is required.
c
if (m-n4pow*2) 40, 40, 30
30 nn = 2
int = n/nn
call fr2tr(int, b(1), b(int+1))
go to 50
40 nn = 1
c
c perform radix 4 iterations.
c
50 if (n4pow.eq.0) go to 70
do 60 it=1,n4pow
nn = nn*4
int = n/nn
call fr4tr(int, nn, b(1), b(int+1), b(2*int+1), b(3*int+1),
* b(1), b(int+1), b(2*int+1), b(3*int+1))
60 continue
c
c perform in-place reordering.
c
70 call ford1(m, b)
call ford2(m, b)
t = b(2)
b(2) = 0.
b(n+1) = t
b(n+2) = 0.
do 80 it=4,n,2
b(it) = -b(it)
80 continue
return
end
|
