sysdeps/libm-ieee754/s_nearbyint.c

   1 /* Adapted for use as nearbyint by Ulrich Drepper <drepper@cygnus.com>.  */
   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 <fenv.h>
  28 #include "math.h"
  29 #include "math_private.h"
  30
  31 #ifdef __STDC__
  32 static const double
  33 #else
  34 static double
  35 #endif
  36 TWO52[2]={
  37   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  38  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  39 };
  40
  41 #ifdef __STDC__
  42         double __nearbyint(double x)
  43 #else
  44         double __nearbyint(x)
  45         double x;
  46 #endif
  47 {
  48         fenv_t env;
  49         int32_t i0,j0,sx;
  50         u_int32_t i,i1;
  51         double w,t;
  52         EXTRACT_WORDS(i0,i1,x);
  53         sx = (i0>>31)&1;
  54         j0 = ((i0>>20)&0x7ff)-0x3ff;
  55         if(j0<20) {
  56             if(j0<0) {
  57                 if(((i0&0x7fffffff)|i1)==0) return x;
  58                 i1 |= (i0&0x0fffff);
  59                 i0 &= 0xfffe0000;
  60                 i0 |= ((i1|-i1)>>12)&0x80000;
  61                 SET_HIGH_WORD(x,i0);
  62                 feholdexcept (&env);
  63                 w = TWO52[sx]+x;
  64                 t =  w-TWO52[sx];
  65                 fesetenv (&env);
  66                 GET_HIGH_WORD(i0,t);
  67                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  68                 return t;
  69             } else {
  70                 i = (0x000fffff)>>j0;
  71                 if(((i0&i)|i1)==0) return x; /* x is integral */
  72                 i>>=1;
  73                 if(((i0&i)|i1)!=0) {
  74                     if(j0==19) i1 = 0x40000000; else
  75                     i0 = (i0&(~i))|((0x20000)>>j0);
  76                 }
  77             }
  78         } else if (j0>51) {
  79             if(j0==0x400) return x+x;   /* inf or NaN */
  80             else return x;              /* x is integral */
  81         } else {
  82             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  83             if((i1&i)==0) return x;     /* x is integral */
  84             i>>=1;
  85             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  86         }
  87         INSERT_WORDS(x,i0,i1);
  88         feholdexcept (&env);
  89         w = TWO52[sx]+x;
  90         t = w-TWO52[sx];
  91         fesetenv (&env);
  92         return t;
  93 }
  94 weak_alias (__nearbyint, nearbyint)
  95 #ifdef NO_LONG_DOUBLE
  96 strong_alias (__nearbyint, __nearbyintl)
  97 weak_alias (__nearbyint, nearbyintl)
  98 #endif