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#include <u.h>
#include <libc.h>
vlong t0, Δt;
double
fac(double n)
{
double Π;
Π = 1;
assert(n > 0);
while(n > 1)
Π *= n--;
return Π;
}
double
bincoeff(double n, double k)
{
assert(k <= n);
return fac(n)/(fac(k)*fac(n-k));
}
double
bincoeffmul(double n, double k)
{
double Π;
int i;
assert(k <= n);
Π = 1;
for(i = 1; i <= k; i++)
Π *= (n + 1 - i)/i;
return Π;
}
void
usage(void)
{
fprint(2, "usage: bincoeff n k\n");
exits("usage");
}
void
main(int argc, char *argv[])
{
double n, k, bc;
if(argc != 3)
usage();
n = strtod(argv[1], nil);
k = strtod(argv[2], nil);
t0 = nsec();
bc = bincoeff(n, k);
Δt = nsec()-t0;
print("method 1: %g (%lldns)\n", bc, Δt);
t0 = nsec();
bc = bincoeffmul(n, k);
Δt = nsec()-t0;
print("method 2: %g (%lldns)\n", bc, Δt);
exits(nil);
}
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