libm/s_rint.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * rint(x)
  14  * Return x rounded to integral value according to the prevailing
  15  * rounding mode.
  16  * Method:
  17  *      Using floating addition.
  18  * Exception:
  19  *      Inexact flag raised if x not equal to rint(x).
  20  */
  21
  22 #include "math.h"
  23 #include "math_private.h"
  24
  25 static const double
  26 TWO52[2]={
  27   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  28  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  29 };
  30
  31 double rint(double x)
  32 {
  33         int32_t i0,j0,sx;
  34         u_int32_t i,i1;
  35         double w,t;
  36         EXTRACT_WORDS(i0,i1,x);
  37         sx = (i0>>31)&1;
  38         j0 = ((i0>>20)&0x7ff)-0x3ff;
  39         if(j0<20) {
  40             if(j0<0) {
  41                 if(((i0&0x7fffffff)|i1)==0) return x;
  42                 i1 |= (i0&0x0fffff);
  43                 i0 &= 0xfffe0000;
  44                 i0 |= ((i1|-i1)>>12)&0x80000;
  45                 SET_HIGH_WORD(x,i0);
  46                 w = TWO52[sx]+x;
  47                 t =  w-TWO52[sx];
  48                 GET_HIGH_WORD(i0,t);
  49                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  50                 return t;
  51             } else {
  52                 i = (0x000fffff)>>j0;
  53                 if(((i0&i)|i1)==0) return x; /* x is integral */
  54                 i>>=1;
  55                 if(((i0&i)|i1)!=0) {
  56                     if(j0==19) i1 = 0x40000000; else
  57                     i0 = (i0&(~i))|((0x20000)>>j0);
  58                 }
  59             }
  60         } else if (j0>51) {
  61             if(j0==0x400) return x+x;   /* inf or NaN */
  62             else return x;              /* x is integral */
  63         } else {
  64             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  65             if((i1&i)==0) return x;     /* x is integral */
  66             i>>=1;
  67             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  68         }
  69         INSERT_WORDS(x,i0,i1);
  70         w = TWO52[sx]+x;
  71         return w-TWO52[sx];
  72 }
  73 libm_hidden_def(rint)
  74
  75 strong_alias(rint, nearbyint)
  76 libm_hidden_def(nearbyint)