src/math/logb.c

   1 #include <math.h>
   2
   3 /*
   4 special cases:
   5         logb(+-0) = -inf, and raise divbyzero
   6         logb(+-inf) = +inf
   7         logb(nan) = nan
   8 */
   9
  10 double logb(double x)
  11 {
  12         if (!isfinite(x))
  13                 return x * x;
  14         if (x == 0)
  15                 return -1/(x*x);
  16         return ilogb(x);
  17 }