sysdeps/ieee754/dbl-64/s_rint.c

   1 /* @(#)s_rint.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_rint.c,v 1.8 1995/05/10 20:48:04 jtc Exp $";
  15 #endif
  16
  17 /*
  18  * rint(x)
  19  * Return x rounded to integral value according to the prevailing
  20  * rounding mode.
  21  * Method:
  22  *      Using floating addition.
  23  * Exception:
  24  *      Inexact flag raised if x not equal to rint(x).
  25  */
  26
  27 #include "math.h"
  28 #include "math_private.h"
  29
  30 #ifdef __STDC__
  31 static const double
  32 #else
  33 static double
  34 #endif
  35 TWO52[2]={
  36   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  37  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  38 };
  39
  40 #ifdef __STDC__
  41         double __rint(double x)
  42 #else
  43         double __rint(x)
  44         double x;
  45 #endif
  46 {
  47         int32_t i0,j0,sx;
  48         u_int32_t i,i1;
  49         double w,t;
  50         EXTRACT_WORDS(i0,i1,x);
  51         sx = (i0>>31)&1;
  52         j0 = ((i0>>20)&0x7ff)-0x3ff;
  53         if(j0<20) {
  54             if(j0<0) {
  55                 if(((i0&0x7fffffff)|i1)==0) return x;
  56                 i1 |= (i0&0x0fffff);
  57                 i0 &= 0xfffe0000;
  58                 i0 |= ((i1|-i1)>>12)&0x80000;
  59                 SET_HIGH_WORD(x,i0);
  60                 w = TWO52[sx]+x;
  61                 t =  w-TWO52[sx];
  62                 GET_HIGH_WORD(i0,t);
  63                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  64                 return t;
  65             } else {
  66                 i = (0x000fffff)>>j0;
  67                 if(((i0&i)|i1)==0) return x; /* x is integral */
  68                 i>>=1;
  69                 if(((i0&i)|i1)!=0) {
  70                     if (j0==19)
  71                       i1 = 0x40000000;
  72                     else if (j0<18)
  73                       i0 = (i0&(~i))|((0x20000)>>j0);
  74                     else
  75                       {
  76                         i0 &= ~i;
  77                         i1 = 0x80000000;
  78                       }
  79                 }
  80             }
  81         } else if (j0>51) {
  82             if(j0==0x400) return x+x;   /* inf or NaN */
  83             else return x;              /* x is integral */
  84         } else {
  85             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  86             if((i1&i)==0) return x;     /* x is integral */
  87             i>>=1;
  88             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  89         }
  90         INSERT_WORDS(x,i0,i1);
  91         w = TWO52[sx]+x;
  92         return w-TWO52[sx];
  93 }
  94 weak_alias (__rint, rint)
  95 #ifdef NO_LONG_DOUBLE
  96 strong_alias (__rint, __rintl)
  97 weak_alias (__rint, rintl)
  98 #endif