lib/msun/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 #ifndef lint
  14 static char rcsid[] = "$FreeBSD$";
  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 /*
  31  * TWO23 is long double instead of double to avoid a bug in gcc.  Without
  32  * this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
  33  * precision and doesn't clip them to double precision when they are
  34  * assigned and returned.  Use long double even in the !__STDC__ case in
  35  * case this is compiled with gcc -traditional.
  36  */
  37 static const long double
  38 TWO52[2]={
  39   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  40  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  41 };
  42
  43         double __generic_rint(double x)
  44 {
  45         int32_t i0,j0,sx;
  46         u_int32_t i,i1;
  47         double w,t;
  48         EXTRACT_WORDS(i0,i1,x);
  49         sx = (i0>>31)&1;
  50         j0 = ((i0>>20)&0x7ff)-0x3ff;
  51         if(j0<20) {
  52             if(j0<0) {
  53                 if(((i0&0x7fffffff)|i1)==0) return x;
  54                 i1 |= (i0&0x0fffff);
  55                 i0 &= 0xfffe0000;
  56                 i0 |= ((i1|-i1)>>12)&0x80000;
  57                 SET_HIGH_WORD(x,i0);
  58                 w = TWO52[sx]+x;
  59                 t =  w-TWO52[sx];
  60                 GET_HIGH_WORD(i0,t);
  61                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  62                 return t;
  63             } else {
  64                 i = (0x000fffff)>>j0;
  65                 if(((i0&i)|i1)==0) return x; /* x is integral */
  66                 i>>=1;
  67                 if(((i0&i)|i1)!=0) {
  68                     if(j0==19) i1 = 0x40000000; else
  69                     i0 = (i0&(~i))|((0x20000)>>j0);
  70                 }
  71             }
  72         } else if (j0>51) {
  73             if(j0==0x400) return x+x;   /* inf or NaN */
  74             else return x;              /* x is integral */
  75         } else {
  76             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  77             if((i1&i)==0) return x;     /* x is integral */
  78             i>>=1;
  79             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  80         }
  81         INSERT_WORDS(x,i0,i1);
  82         w = TWO52[sx]+x;
  83         return w-TWO52[sx];
  84 }