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c
c-----------------------------------------------------------------------
c subroutine: fr4syn
c radix 4 synthesis
c-----------------------------------------------------------------------
c
c
subroutine fr4syn(int, nn, b0, b1, b2, b3, b4, b5, b6, b7)
dimension l(15), b0(2), b1(2), b2(2), b3(2), b4(2), b5(2), b6(2),
* b7(2)
common /const/ pii, p7, p7two, c22, s22, pi2
equivalence (l15,l(1)), (l14,l(2)), (l13,l(3)), (l12,l(4)),
* (l11,l(5)), (l10,l(6)), (l9,l(7)), (l8,l(8)), (l7,l(9)),
* (l6,l(10)), (l5,l(11)), (l4,l(12)), (l3,l(13)), (l2,l(14)),
* (l1,l(15))
c
l(1) = nn/4
do 40 k=2,15
if (l(k-1)-2) 10, 20, 30
10 l(k-1) = 2
20 l(k) = 2
go to 40
30 l(k) = l(k-1)/2
40 continue
c
piovn = pii/float(nn)
ji = 3
jl = 2
jr = 2
c
do 120 j1=2,l1,2
do 120 j2=j1,l2,l1
do 120 j3=j2,l3,l2
do 120 j4=j3,l4,l3
do 120 j5=j4,l5,l4
do 120 j6=j5,l6,l5
do 120 j7=j6,l7,l6
do 120 j8=j7,l8,l7
do 120 j9=j8,l9,l8
do 120 j10=j9,l10,l9
do 120 j11=j10,l11,l10
do 120 j12=j11,l12,l11
do 120 j13=j12,l13,l12
do 120 j14=j13,l14,l13
do 120 jthet=j14,l15,l14
th2 = jthet - 2
if (th2) 50, 50, 90
50 do 60 k=1,int
t0 = b0(k) + b1(k)
t1 = b0(k) - b1(k)
t2 = b2(k)*2.0
t3 = b3(k)*2.0
b0(k) = t0 + t2
b2(k) = t0 - t2
b1(k) = t1 + t3
b3(k) = t1 - t3
60 continue
c
if (nn-4) 120, 120, 70
70 k0 = int*4 + 1
kl = k0 + int - 1
do 80 k=k0,kl
t2 = b0(k) - b2(k)
t3 = b1(k) + b3(k)
b0(k) = (b0(k)+b2(k))*2.0
b2(k) = (b3(k)-b1(k))*2.0
b1(k) = (t2+t3)*p7two
b3(k) = (t3-t2)*p7two
80 continue
go to 120
90 arg = th2*piovn
c1 = cos(arg)
s1 = -sin(arg)
c2 = c1**2 - s1**2
s2 = c1*s1 + c1*s1
c3 = c1*c2 - s1*s2
s3 = c2*s1 + s2*c1
c
int4 = int*4
j0 = jr*int4 + 1
k0 = ji*int4 + 1
jlast = j0 + int - 1
do 100 j=j0,jlast
k = k0 + j - j0
t0 = b0(j) + b6(k)
t1 = b7(k) - b1(j)
t2 = b0(j) - b6(k)
t3 = b7(k) + b1(j)
t4 = b2(j) + b4(k)
t5 = b5(k) - b3(j)
t6 = b5(k) + b3(j)
t7 = b4(k) - b2(j)
b0(j) = t0 + t4
b4(k) = t1 + t5
b1(j) = (t2+t6)*c1 - (t3+t7)*s1
b5(k) = (t2+t6)*s1 + (t3+t7)*c1
b2(j) = (t0-t4)*c2 - (t1-t5)*s2
b6(k) = (t0-t4)*s2 + (t1-t5)*c2
b3(j) = (t2-t6)*c3 - (t3-t7)*s3
b7(k) = (t2-t6)*s3 + (t3-t7)*c3
100 continue
jr = jr + 2
ji = ji - 2
if (ji-jl) 110, 110, 120
110 ji = 2*jr - 1
jl = jr
120 continue
return
end
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