How to alter a float by its smallest increment (or close to it)?

Question

I have a double value f and would like a way to nudge it very slightly larger (or smaller) to get a new value that will be as close as possible to

Answer 1

I needed to do the exact same thing and came up with this code:

double DoubleIncrement(double value)
{
  int exponent;
  double mantissa = frexp(value, &exponent);
  if(mantissa == 0)
    return DBL_MIN;

  mantissa += DBL_EPSILON/2.0f;
  value = ldexp(mantissa, exponent);
  return value;
}