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var pi = 3.14159265358979323846;
var tpi = 2.0 * pi;
function fft (px, py, np) {
var i = 2;
var m = 1;
while (i < np) {
i = i + i;
m ++;
}
var n = i;
if (n != np) {
for (i = np+1; i <= n; i++) {
px[i] = 0;
py[i] = 0;
}
}
var n2 = n + n;
for (var k = 1; k < m; k++) {
n2 = n2 / 2;
var n4 = n2 / 4;
var e = tpi / n2;
for (var j = 1; j <= n4; j++) {
var a = e * (j - 1);
var a3 = 3.0 * a;
var cc1 = Math.cos(a);
var ss1 = Math.sin(a);
var cc3 = Math.cos(a3);
var ss3 = Math.sin(a3);
var is = j;
var id = 2 * n2;
while (is < n) {
var i0r = is;
while (i0r < n) {
var i0 = i0r;
var i1 = i0 + n4;
var i2 = i1 + n4;
var i3 = i2 + n4;
var r1 = px[i0] - px[i2];
px[i0] += px[i2];
var r2 = px[i1] - px[i3];
px[i1] += px[i3];
var s1 = py[i0] - py[i2];
py[i0] += py[i2];
var s2 = py[i1] - py[i3];
py[i1] += py[i3];
var s3 = r1 - s2;
var r1 = r1 + s2;
var s2 = r2 - s1;
var r2 = r2 + s1;
px[i2] = r1*cc1 - s2*ss1;
py[i2] = -s2*cc1 - r1*ss1;
px[i3] = s3*cc3 + r2*ss3;
py[i3] = r2*cc3 - s3*ss3;
i0r = i0 + id
}
is = 2 * id - n2 + j;
id = 4 * id
}
}
};
/************************************/
/* Last stage, length=2 butterfly */
/************************************/
var is = 1;
var id = 4;
while (is < n) {
var i0r = is;
while (i0r <= n) {
var i0 = i0r;
var i1 = i0 + 1;
var r1 = px[i0];
px[i0] = r1 + px[i1];
px[i1] = r1 - px[i1];
var r1 = py[i0];
py[i0] = r1 + py[i1];
py[i1] = r1 - py[i1];
i0r = i0 + id
};
is = 2 * id - 1;
id = 4 * id
};
/*************************/
/* Bit reverse counter */
/*************************/
var j = 1;
for (var i = 1; i < n; i++) {
if (i < j) {
var xt = px[j];
px[j] = px[i];
px[i] = xt;
var xt = py[j];
py[j] = py[i];
py[i] = xt
}
var k = n / 2;
while (k < j) {
j = j - k;
k = k / 2
};
j = j + k
};
return n;
}
function test (np) {
/* print_int np; print_string "... "; flush stdout;*/
var enp = np;
var npm = np / 2 - 1;
var pxr = [];
var pxi = [];
for (var i = 0; i < np +2; i++) {
pxr[i] = 0.0;
pxi[i] = 0.0;
}
var t = pi / enp;
pxr[1] = (enp - 1.0) * 0.5;
pxi[1] = 0.0;
var n2 = np / 2;
pxr[n2+1] = -0.5;
pxi[n2+1] = 0.0;
for (var i = 1; i <= npm; i++) {
var j = np - i;
pxr[i+1] = -0.5;
pxr[j+1] = -0.5;
var z = t * i;
var y = -0.5*(Math.cos(z)/Math.sin(z));
pxi[i+1] = y;
pxi[j+1] = -y
};
/**
print_newline();
for i=0 to 15 do Printf.printf "%d %f %f\n" i pxr[i+1) pxi[i+1] done;
**/
fft (pxr, pxi, np);
/**
for i=0 to 15 do Printf.printf "%d %f %f\n" i pxr[i+1] pxi[i+1] done;
.**/
var zr = 0.0;
var zi = 0.0;
var kr = 0;
var ki = 0;
for (var i = 0; i < np; i++) {
var a = Math.abs (pxr[i+1] - i);
if (zr < a) {
zr = a;
kr = i;
}
var a = Math.abs(pxi[i+1]);
if (zi < a) {
zi = a;
ki = i;
}
}
// print (zr); print (zi);
if (Math.abs( zr) <= 1e-8 && Math.abs( zi) <= 1e-8) {} else throw "ERROR";
}
var np = 16; for (var i = 1; i<= 16; i++) { test (np); np = np*2; }
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