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/********************************************************/
/* A Duhamel-Hollman split-radix dif fft */
/* Ref: Electronics Letters, Jan. 5, 1984 */
/* Complex input and output data in arrays x and y */
/* Length is n. */
/********************************************************/
extern "cos" : float -> float
extern "sin" : float -> float
"dfft"(x, y, np): int /*float ptr*/ -> int /*float ptr*/ -> int -> int
{
var px, py, /*float ptr*/
i, j, k, m, n, i0, i1, i2, i3, is, id, n1, n2, n4, a, e, a3, /*int*/
cc1, ss1, cc3, ss3, r1, r2, s1, s2, s3, xt, tpi /*float*/;
px = x - 8;
py = y - 8;
i = 2;
m = 1;
{{ loop {
if (! (i < np)) exit;
i = i+i;
m = m+1;
} }}
n = i;
if (n != np)
{
i = np + 1;
{{ loop {
if (! (i <= n)) exit;
float64[px + i*8] = 0.0;
float64[py + i*8] = 0.0;
i = i + 1;
} }}
}
n2 = n+n;
tpi = 2.0 *f 3.14159265358979323846;
k = 1;
{{ loop {
if (! (k <= m - 1)) exit;
n2 = n2 / 2;
n4 = n2 / 4;
e = tpi /f floatofint(n2);
a = 0.0;
j = 1;
{{ loop {
if (! (j <= n4)) exit;
cc1 = "cos"(a) : float -> float;
ss1 = "sin"(a) : float -> float;
a3 = 3.0 *f a;
cc3 = "cos"(a3) : float -> float;
ss3 = "sin"(a3) : float -> float;
a = e *f floatofint(j);
is = j;
id = 2 * n2;
{{ loop {
if (! ( is < n )) exit;
i0 = is;
{{ loop {
/* DEBUG "trace"(); */
if (! (i0 <= n - 1)) exit;
i1 = i0 + n4; /*DEBUG "print_int"(i1); */
i2 = i1 + n4; /*DEBUG "print_int"(i2); */
i3 = i2 + n4; /*DEBUG "print_int"(i3); */
r1 = float64[px+i0*8] -f float64[px+i2*8];
/* DEBUG "print_float"(r1); */
float64[px+i0*8] = float64[px+i0*8] +f float64[px+i2*8];
r2 = float64[px+i1*8] -f float64[px+i3*8];
/* DEBUG "print_float"(r2); */
float64[px+i1*8] = float64[px+i1*8] +f float64[px+i3*8];
s1 = float64[py+i0*8] -f float64[py+i2*8];
/* DEBUG "print_float"(s1); */
float64[py+i0*8] = float64[py+i0*8] +f float64[py+i2*8];
s2 = float64[py+i1*8] -f float64[py+i3*8];
/* DEBUG "print_float"(s2); */
float64[py+i1*8] = float64[py+i1*8] +f float64[py+i3*8];
s3 = r1 -f s2; r1 = r1 +f s2;
s2 = r2 -f s1; r2 = r2 +f s1;
float64[px+i2*8] = (r1 *f cc1) -f (s2 *f ss1);
float64[py+i2*8] = (-f s2 *f cc1) -f (r1 *f ss1);
float64[px+i3*8] = (s3 *f cc3) +f (r2 *f ss3);
float64[py+i3*8] = (r2 *f cc3) -f (s3 *f ss3);
i0 = i0 + id;
} }}
is = 2 * id - n2 + j;
id = 4 * id;
} }}
j = j + 1;
} }}
k = k + 1;
} }}
/************************************/
/* Last stage, length=2 butterfly */
/************************************/
is = 1;
id = 4;
{{ loop {
if (! ( is < n)) exit;
i0 = is;
{{ loop {
if (! (i0 <= n)) exit;
i1 = i0 + 1;
r1 = float64[px+i0*8];
float64[px+i0*8] = r1 +f float64[px+i1*8];
float64[px+i1*8] = r1 -f float64[px+i1*8];
r1 = float64[py+i0*8];
float64[py+i0*8] = r1 +f float64[py+i1*8];
float64[py+i1*8] = r1 -f float64[py+i1*8];
i0 = i0 + id;
} }}
is = 2*id - 1;
id = 4 * id;
} }}
/*************************/
/* Bit reverse counter */
/*************************/
j = 1;
n1 = n - 1;
i = 1;
{{ loop {
if (! (i <= n1)) exit;
if (i < j) {
xt = float64[px+j*8];
float64[px+j*8] = float64[px+i*8];
float64[px+i*8] = xt;
xt = float64[py+j*8];
float64[py+j*8] = float64[py+i*8];
float64[py+i*8] = xt;
}
k = n / 2;
{{ loop {
if (! (k < j)) exit;
j = j - k;
k = k / 2;
} }}
j = j + k;
i = i + 1;
} }}
return(n);
}
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