1#include <math.h>
2#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
3long double logbl(long double x)
4{
5	return logb(x);
6}
7#else
8long double logbl(long double x)
9{
10	if (!isfinite(x))
11		return x * x;
12	if (x == 0)
13		return -1/(x*x);
14	return ilogbl(x);
15}
16#endif
17