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  * $FreeBSD: src/lib/msun/src/s_rint.c,v 1.7 1999/08/28 00:06:54 peter Exp $
  13  * $DragonFly: src/lib/msun/src/Attic/s_rint.c,v 1.2 2003/06/17 04:26:53 dillon Exp $
  14  */
  15
  16 /*
  17  * rint(x)
  18  * Return x rounded to integral value according to the prevailing
  19  * rounding mode.
  20  * Method:
  21  *      Using floating addition.
  22  * Exception:
  23  *      Inexact flag raised if x not equal to rint(x).
  24  */
  25
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 /*
  30  * TWO23 is long double instead of double to avoid a bug in gcc.  Without
  31  * this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
  32  * precision and doesn't clip them to double precision when they are
  33  * assigned and returned.  Use long double even in the !__STDC__ case in
  34  * case this is compiled with gcc -traditional.
  35  */
  36 #ifdef __STDC__
  37 static const long double
  38 #else
  39 static long double
  40 #endif
  41 TWO52[2]={
  42   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  43  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  44 };
  45
  46 #ifdef __STDC__
  47         double __generic_rint(double x)
  48 #else
  49         double __generic_rint(x)
  50         double x;
  51 #endif
  52 {
  53         int32_t i0,j0,sx;
  54         u_int32_t i,i1;
  55         double w,t;
  56         EXTRACT_WORDS(i0,i1,x);
  57         sx = (i0>>31)&1;
  58         j0 = ((i0>>20)&0x7ff)-0x3ff;
  59         if(j0<20) {
  60             if(j0<0) {
  61                 if(((i0&0x7fffffff)|i1)==0) return x;
  62                 i1 |= (i0&0x0fffff);
  63                 i0 &= 0xfffe0000;
  64                 i0 |= ((i1|-i1)>>12)&0x80000;
  65                 SET_HIGH_WORD(x,i0);
  66                 w = TWO52[sx]+x;
  67                 t =  w-TWO52[sx];
  68                 GET_HIGH_WORD(i0,t);
  69                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  70                 return t;
  71             } else {
  72                 i = (0x000fffff)>>j0;
  73                 if(((i0&i)|i1)==0) return x; /* x is integral */
  74                 i>>=1;
  75                 if(((i0&i)|i1)!=0) {
  76                     if(j0==19) i1 = 0x40000000; else
  77                     i0 = (i0&(~i))|((0x20000)>>j0);
  78                 }
  79             }
  80         } else if (j0>51) {
  81             if(j0==0x400) return x+x;   /* inf or NaN */
  82             else return x;              /* x is integral */
  83         } else {
  84             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  85             if((i1&i)==0) return x;     /* x is integral */
  86             i>>=1;
  87             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  88         }
  89         INSERT_WORDS(x,i0,i1);
  90         w = TWO52[sx]+x;
  91         return w-TWO52[sx];
  92 }