-#include <limits.h>
#include "libm.h"
/*
special cases:
- logb(+-0) = -inf
+ logb(+-0) = -inf, and raise divbyzero
logb(+-inf) = +inf
logb(nan) = nan
-these are calculated at runtime to raise fp exceptions
*/
-double logb(double x) {
- int i = ilogb(x);
-
- if (i == FP_ILOGB0)
- return -1.0/fabs(x);
- if (i == FP_ILOGBNAN || i == INT_MAX)
+double logb(double x)
+{
+ if (!isfinite(x))
return x * x;
- return i;
+ if (x == 0)
+ return -1/(x+0);
+ return ilogb(x);
}