F.9.3.12 The modf functions

1

• modf((+-)x, iptr) returns a result with the same sign as x.

• modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr.

• modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a NaN).

2

modf behaves as though implemented by

#include <math.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
double modf(double value, double *iptr)
{
     int save_round = fegetround();
     fesetround(FE_TOWARDZERO);
     *iptr = nearbyint(value);
     fesetround(save_round);
     return copysign(
          isinf(value) ? 0.0 :
               value - (*iptr), value);
}