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