floor.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 floor(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 || x == 0)
  17  		return x;
  18  	/* y = int(x) - x, where int(x) is an integer neighbor of x */
  19  	if (u.i >> 63)
  20  		y = x - toint + toint - x;
  21  	else
  22  		y = x + toint - toint - x;
  23  	/* special case because of non-nearest rounding modes */
  24  	if (e <= 0x3ff-1) {
  25  		FORCE_EVAL(y);
  26  		return u.i >> 63 ? -1 : 0;
  27  	}
  28  	if (y > 0)
  29  		return x + y - 1;
  30  	return x + y;
  31  }
  32