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 /*
  23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  24  */
  25 /*
  26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  27  * Use is subject to license terms.
  28  */
  29 
  30 #if defined(ELFOBJ)
  31 #pragma weak round = __round
  32 #endif
  33 
  34 #include "libm.h"
  35 
  36 double
  37 round(double x) {
  38         union {
  39                 unsigned i[2];
  40                 double d;
  41         } xx;
  42         unsigned hx, sx, i;
  43 
  44         xx.d = x;
  45         hx = xx.i[HIWORD] & ~0x80000000;
  46         sx = xx.i[HIWORD] & 0x80000000;
  47         if (hx < 0x43300000) {       /* |x| < 2^52 */
  48                 if (hx < 0x3ff00000) {       /* |x| < 1 */
  49                         if (hx >= 0x3fe00000)
  50                                 return (sx ? -1.0 : 1.0);
  51                         return (sx ? -0.0 : 0.0);
  52                 }
  53 
  54                 /* round x at the integer bit */
  55                 if (hx < 0x41300000) {
  56                         i = 1 << (0x412 - (hx >> 20));
  57                         xx.i[HIWORD] = (xx.i[HIWORD] + i) & ~(i | (i - 1));
  58                         xx.i[LOWORD] = 0;
  59                 } else {
  60                         i = 1 << (0x432 - (hx >> 20));
  61                         xx.i[LOWORD] += i;
  62                         if (xx.i[LOWORD] < i)
  63                                 xx.i[HIWORD]++;
  64                         xx.i[LOWORD] &= ~(i | (i - 1));
  65                 }
  66                 return (xx.d);
  67         } else if (hx < 0x7ff00000)
  68                 return (x);
  69         else
  70 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  71                 return (hx >= 0x7ff80000 ? x : x + x);
  72                 /* assumes sparc-like QNaN */
  73 #else
  74                 return (x + x);
  75 #endif
  76 }