#include <math.h>
#ifdef LONG_DOUBLE_IS_BINARY64
long double logbl(long double x)
{
	return logb(x);
}
#else
long double logbl(long double x)
{
	if (!isfinite(x))
		return x * x;
	if (x == 0)
		return -1/(x*x);
	return ilogbl(x);
}
#endif