Visual C++ 2010 Express で動作確認済
powl()を自作

long double Pow(long double x,long double y){if(x<0&&y-(int)y!=0)return 0;
long double n,m,p,z,l,i,j,c,a;int b,t,f=1;y<0?y=-y,f=0:0;a=x,b=(int)y;i=n=p=1;
for(;i++<=b;)f?n*=a:b?n/=a:0;if(x<0||y-(int)y==0)return n;c=n;for(t=0;t++<20;)
{a=10,b=t;i=0,n=1;for(;i++<b;)n*=a;a=x,b=(int)(y*n)%10;i=0,n=1;for(;i++<b;)n*=
a;z=n;for(j=0;j++<t;){for(l=0;l++<40;){for(i=n=1;i++<40;)n=((1/m*z)/n+n)/2.0;
for(i=m=1;i++<40;)m=(n/m+m)/2.0;p=(m/p+p)/2.0;}z=p;}f?c*=z:c/=z;}return c;}