usr/src/lib/libm/common/C/rint.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  23  */
  24 /*
  25  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  26  * Use is subject to license terms.
  27  */
  28
  29 #pragma weak __rint = rint
  30
  31 /*
  32  * rint(x) return x rounded to integral according to the rounding direction
  33  * rint(x) returns result with the same sign as x's,  including 0.0.
  34  */
  35
  36 #include "libm.h"
  37
  38 #if defined(__i386) && !defined(__amd64) && (!defined(__FLT_EVAL_METHOD__) || \
  39         __FLT_EVAL_METHOD__ != 0)
  40 extern enum fp_precision_type __swapRP(enum fp_precision_type);
  41 #define DECLRP(x)       enum fp_precision_type x;
  42 #define SWAPRP(new, x)  x = __swapRP(new);
  43 #define RESTRP(x)       (void) __swapRP(x);
  44 #else
  45 #define DECLRP(x)
  46 #define SWAPRP(new, x)
  47 #define RESTRP(x)
  48 #endif
  49
  50 static const double
  51         two52 = 4503599627370496.0,
  52         zero = 0.0,
  53         one = 1.0;
  54
  55 double
  56 rint(double x) {
  57         DECLRP(rp)
  58         double  t, w;
  59         int     ix, hx;
  60
  61         ix = ((int *)&x)[HIWORD];
  62         hx = ix & ~0x80000000;
  63
  64         if (hx >= 0x43300000)
  65                 return (x * one);
  66         t = (ix < 0)? -two52 : two52;
  67         SWAPRP(fp_double, rp)           /* set precision mode to double */
  68         w = x + t;                      /* x+sign(x)*2**52 rounded */
  69         RESTRP(rp)                      /* restore precision mode */
  70         if (w == t)
  71                 return ((ix < 0)? -zero : zero);
  72         return (w - t);
  73 }