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: src/lib/msun/src/s_rint.c,v 1.7 1999/08/28 00:06:54 peter 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 "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 #ifdef __STDC__
  38 static const long double
  39 #else
  40 static long double
  41 #endif
  42 TWO52[2]={
  43   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  44  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  45 };
  46
  47 #ifdef __STDC__
  48         double __generic_rint(double x)
  49 #else
  50         double __generic_rint(x)
  51         double x;
  52 #endif
  53 {
  54         int32_t i0,j0,sx;
  55         u_int32_t i,i1;
  56         double w,t;
  57         EXTRACT_WORDS(i0,i1,x);
  58         sx = (i0>>31)&1;
  59         j0 = ((i0>>20)&0x7ff)-0x3ff;
  60         if(j0<20) {
  61             if(j0<0) {
  62                 if(((i0&0x7fffffff)|i1)==0) return x;
  63                 i1 |= (i0&0x0fffff);
  64                 i0 &= 0xfffe0000;
  65                 i0 |= ((i1|-i1)>>12)&0x80000;
  66                 SET_HIGH_WORD(x,i0);
  67                 w = TWO52[sx]+x;
  68                 t =  w-TWO52[sx];
  69                 GET_HIGH_WORD(i0,t);
  70                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  71                 return t;
  72             } else {
  73                 i = (0x000fffff)>>j0;
  74                 if(((i0&i)|i1)==0) return x; /* x is integral */
  75                 i>>=1;
  76                 if(((i0&i)|i1)!=0) {
  77                     if(j0==19) i1 = 0x40000000; else
  78                     i0 = (i0&(~i))|((0x20000)>>j0);
  79                 }
  80             }
  81         } else if (j0>51) {
  82             if(j0==0x400) return x+x;   /* inf or NaN */
  83             else return x;              /* x is integral */
  84         } else {
  85             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  86             if((i1&i)==0) return x;     /* x is integral */
  87             i>>=1;
  88             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  89         }
  90         INSERT_WORDS(x,i0,i1);
  91         w = TWO52[sx]+x;
  92         return w-TWO52[sx];
  93 }