floor, ceil, fabs, rint - floor, ceiling, absolute value,  and  round-to-
     nearest functions

     #include <math.h>

     double floor(double x)
     double ceil(double x)
     double fabs(double x)
     double rint(double x)

     Floor returns the largest integer no greater than x.

     Ceil returns the smallest integer no less than x.

     Fabs returns the absolute value |x|.

     Rint returns the integer  (represented  as  a  double  precision  number)
     nearest x in the direction of the prevailing rounding mode.

     In the default rounding mode, to nearest, rint(x) is the integer  nearest
     x  with the additional stipulation that if |rint(x)-x| = 1/2 then rint(x)
     is even.  Other rounding modes can make rint  act  like  floor,  or  like
     ceil, or round towards zero.

     Another way to obtain an integer near x is to declare (in C)

          double x;     int k;    k = x;

     Most C compilers round x towards 0 to get the  integer  k,  but  some  do
     otherwise.   If  in  doubt, use floor, ceil, or rint first, whichever you
     intend.  Also note that, if x is larger than k can accommodate, the value
     of  k  and  the  presence  or  absence of an integer overflow are hard to

     abs(3), ieee(3), math(3).