lib/libm/src/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 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_rint.c,v 1.12 2008/04/25 22:21:53 christos Exp $");
  16 #endif
  17
  18 /*
  19  * rint(x)
  20  * Return x rounded to integral value according to the prevailing
  21  * rounding mode.
  22  * Method:
  23  *      Using floating addition.
  24  * Exception:
  25  *      Inexact flag raised if x not equal to rint(x).
  26  */
  27
  28 #include "math.h"
  29 #include "math_private.h"
  30
  31 static const double
  32 TWO52[2]={
  33   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  34  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  35 };
  36
  37 double
  38 rint(double x)
  39 {
  40         int32_t i0,jj0,sx;
  41         u_int32_t i,i1;
  42         double w,t;
  43         EXTRACT_WORDS(i0,i1,x);
  44         sx = (i0>>31)&1;
  45         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  46         if(jj0<20) {
  47             if(jj0<0) {
  48                 if(((i0&0x7fffffff)|i1)==0) return x;
  49                 i1 |= (i0&0x0fffff);
  50                 i0 &= 0xfffe0000;
  51                 i0 |= ((i1|-i1)>>12)&0x80000;
  52                 SET_HIGH_WORD(x,i0);
  53                 w = TWO52[sx]+x;
  54                 t =  w-TWO52[sx];
  55                 GET_HIGH_WORD(i0,t);
  56                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  57                 return t;
  58             } else {
  59                 i = (0x000fffff)>>jj0;
  60                 if(((i0&i)|i1)==0) return x; /* x is integral */
  61                 i>>=1;
  62                 if(((i0&i)|i1)!=0) {
  63                     if(jj0==19) i1 = 0x40000000; else
  64                     i0 = (i0&(~i))|((0x20000)>>jj0);
  65                 }
  66             }
  67         } else if (jj0>51) {
  68             if(jj0==0x400) return x+x;  /* inf or NaN */
  69             else return x;              /* x is integral */
  70         } else {
  71             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  72             if((i1&i)==0) return x;     /* x is integral */
  73             i>>=1;
  74             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
  75         }
  76         INSERT_WORDS(x,i0,i1);
  77         w = TWO52[sx]+x;
  78         return w-TWO52[sx];
  79 }