round.c raw

   1  #include "libm.h"
   2  
   3  #if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
   4  #define EPS DBL_EPSILON
   5  #elif FLT_EVAL_METHOD==2
   6  #define EPS LDBL_EPSILON
   7  #endif
   8  static const double_t toint = 1/EPS;
   9  
  10  double round(double x)
  11  {
  12  	union {double f; uint64_t i;} u = {x};
  13  	int e = u.i >> 52 & 0x7ff;
  14  	double_t y;
  15  
  16  	if (e >= 0x3ff+52)
  17  		return x;
  18  	if (u.i >> 63)
  19  		x = -x;
  20  	if (e < 0x3ff-1) {
  21  		/* raise inexact if x!=0 */
  22  		FORCE_EVAL(x + toint);
  23  		return 0*u.f;
  24  	}
  25  	y = x + toint - toint - x;
  26  	if (y > 0.5)
  27  		y = y + x - 1;
  28  	else if (y <= -0.5)
  29  		y = y + x + 1;
  30  	else
  31  		y = y + x;
  32  	if (u.i >> 63)
  33  		y = -y;
  34  	return y;
  35  }
  36