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  * $NetBSD: s_rint.c,v 1.12 2008/04/25 22:21:53 christos Exp $
  13  */
  14
  15 /*
  16  * rint(x)
  17  * Return x rounded to integral value according to the prevailing
  18  * rounding mode.
  19  * Method:
  20  *      Using floating addition.
  21  * Exception:
  22  *      Inexact flag raised if x not equal to rint(x).
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double
  29 TWO52[2]={
  30   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  31  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  32 };
  33
  34 double
  35 rint(double x)
  36 {
  37         int32_t i0,jj0,sx;
  38         u_int32_t i,i1;
  39         double w,t;
  40         EXTRACT_WORDS(i0,i1,x);
  41         sx = (i0>>31)&1;
  42         jj0 = ((i0>>20)&0x7ff)-0x3ff;
  43         if(jj0<20) {
  44             if(jj0<0) {
  45                 if(((i0&0x7fffffff)|i1)==0) return x;
  46                 i1 |= (i0&0x0fffff);
  47                 i0 &= 0xfffe0000;
  48                 i0 |= ((i1|-i1)>>12)&0x80000;
  49                 SET_HIGH_WORD(x,i0);
  50                 w = TWO52[sx]+x;
  51                 t =  w-TWO52[sx];
  52                 GET_HIGH_WORD(i0,t);
  53                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  54                 return t;
  55             } else {
  56                 i = (0x000fffff)>>jj0;
  57                 if(((i0&i)|i1)==0) return x; /* x is integral */
  58                 i>>=1;
  59                 if(((i0&i)|i1)!=0) {
  60                     if(jj0==19) i1 = 0x40000000; else
  61                     i0 = (i0&(~i))|((0x20000)>>jj0);
  62                 }
  63             }
  64         } else if (jj0>51) {
  65             if(jj0==0x400) return x+x;  /* inf or NaN */
  66             else return x;              /* x is integral */
  67         } else {
  68             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  69             if((i1&i)==0) return x;     /* x is integral */
  70             i>>=1;
  71             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
  72         }
  73         INSERT_WORDS(x,i0,i1);
  74         w = TWO52[sx]+x;
  75         return w-TWO52[sx];
  76 }