sysdeps/generic/rint.c

   1 /* snarfed from BSD common_source/floor.c:
   2  * Copyright (c) 1985, 1995 Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #ifndef lint
  35 static char sccsid[] = "@(#)floor.c     5.7 (Berkeley) 10/9/90";
  36 #endif /* not lint */
  37
  38 #include "mathimpl.h"
  39
  40 vc(L, 4503599627370496.0E0 ,0000,5c00,0000,0000, 55, 1.0) /* 2**55 */
  41
  42 ic(L, 4503599627370496.0E0, 52, 1.0)                      /* 2**52 */
  43
  44 #ifdef vccast
  45 #define L       vccast(L)
  46 #endif
  47
  48 /*
  49  * algorithm for rint(x) in pseudo-pascal form ...
  50  *
  51  * real rint(x): real x;
  52  *      ... delivers integer nearest x in direction of prevailing rounding
  53  *      ... mode
  54  * const        L = (last consecutive integer)/2
  55  *        = 2**55; for VAX D
  56  *        = 2**52; for IEEE 754 Double
  57  * real s,t;
  58  * begin
  59  *      if x != x then return x;                ... NaN
  60  *      if |x| >= L then return x;              ... already an integer
  61  *      s := copysign(L,x);
  62  *      t := x + s;                             ... = (x+s) rounded to integer
  63  *      return t - s
  64  * end;
  65  *
  66  * Note: Inexact will be signaled if x is not an integer, as is
  67  *      customary for IEEE 754.  No other signal can be emitted.
  68  */
  69 double
  70 __rint(x)
  71 double x;
  72 {
  73         double s,t;
  74         const double one = 1.0;
  75
  76 #if !defined(vax)&&!defined(tahoe)
  77         if (x != x)                             /* NaN */
  78                 return (x);
  79 #endif  /* !defined(vax)&&!defined(tahoe) */
  80         if (copysign(x,one) >= L)               /* already an integer */
  81             return (x);
  82         s = copysign(L,x);
  83         t = x + s;                              /* x+s rounded to integer */
  84         return (t - s);
  85 }
  86
  87 weak_alias (__rint, rint)