static real ChiSquare(creal x, cint df)
{
real y;
if( df <= 0 ) return -999;
if( x <= 0 ) return 0;
if( x > 1000*df ) return 1;
if( df > 1000 ) {
if( x < 2 ) return 0;
y = 2./(9*df);
y = (powx(x/df, 1/3.) - (1 - y))/sqrtx(y);
if( y > 5 ) return 1;
if( y < -18.8055 ) return 0;
return Normal(y);
}
y = .5*x;
if( df & 1 ) {
creal sqrty = sqrtx(y);
real h = Erf(sqrty);
count i;
if( df == 1 ) return h;
y = sqrty*expx(-y)/.8862269254527579825931;
for( i = 3; i < df; i += 2 ) {
h -= y;
y *= x/i;
}
y = h - y;
}
else {
real term = expx(-y), sum = term;
count i;
for( i = 1; i < df/2; ++i )
sum += term *= y/i;
y = 1 - sum;
}
return Max(0., y);
}
void test(Power power)
{
int i = 0;
clock_t t1 = clock();
for(i; i < sizeof(cases)/sizeof(testcase); i++)
{
testcase c = cases[i];
printf("powx(%d, %d) expect %g, got %g\n", c.x, c.n, c.expect, powx(c.x, c.n, power));
}
clock_t t2 = clock();
printf("cost time: %fs\n\n", difftime(t2, t1)/CLOCKS_PER_SEC);
}
static void RefineGrid(cThis *t, Grid grid, Grid margsum)
{
real avgperbin, thisbin, newcur, delta;
Grid imp, newgrid;
int bin, newbin;
/* smooth the f^2 value stored for each bin */
real prev = margsum[0];
real cur = margsum[1];
real norm = margsum[0] = .5*(prev + cur);
for( bin = 1; bin < NBINS - 1; ++bin ) {
creal s = prev + cur;
prev = cur;
cur = margsum[bin + 1];
norm += margsum[bin] = (s + cur)/3.;
}
norm += margsum[NBINS - 1] = .5*(prev + cur);
if( norm == 0 ) return;
norm = 1/norm;
/* compute the importance function for each bin */
avgperbin = 0;
for( bin = 0; bin < NBINS; ++bin ) {
real impfun = 0;
if( margsum[bin] > 0 ) {
creal r = margsum[bin]*norm;
avgperbin += impfun = powx((r - 1)/log(r), 1.5);
}
imp[bin] = impfun;
}
avgperbin /= NBINS;
/* redefine the size of each bin */
cur = newcur = 0;
thisbin = 0;
bin = -1;
for( newbin = 0; newbin < NBINS - 1; ++newbin ) {
while( thisbin < avgperbin ) {
thisbin += imp[++bin];
prev = cur;
cur = grid[bin];
}
thisbin -= avgperbin;
delta = (cur - prev)*thisbin;
newgrid[newbin] = SHARPEDGES ?
cur - delta/imp[bin] :
(newcur = Max(newcur + 16*DBL_EPSILON,
cur - 2*delta/(imp[bin] + imp[IDim(bin - 1)])));
}
Copy(grid, newgrid, NBINS - 1);
grid[NBINS - 1] = 1;
}
int main(){
int a = powx(2,8);
return 0;
}
