src/math/round.c

   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 }