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 /*
  27  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  28  * Use is subject to license terms.
  29  */
  30 
  31 #pragma weak nearbyint = __nearbyint
  32 
  33 /*
  34  * nearbyint(x) returns the nearest fp integer to x in the direction
  35  * corresponding to the current rounding direction without raising
  36  * the inexact exception.
  37  *
  38  * nearbyint(x) is x unchanged if x is +/-0 or +/-inf.  If x is NaN,
  39  * nearbyint(x) is also NaN.
  40  */
  41 
  42 #include "libm.h"
  43 #include <fenv.h>
  44 
  45 double
  46 __nearbyint(double x)
  47 {
  48         union {
  49                 unsigned i[2];
  50                 double d;
  51         } xx;
  52 
  53         unsigned hx, sx, i, frac;
  54         int rm, j;
  55 
  56         xx.d = x;
  57         sx = xx.i[HIWORD] & 0x80000000;
  58         hx = xx.i[HIWORD] & ~0x80000000;
  59 
  60         /* handle trivial cases */
  61         if (hx >= 0x43300000) {              /* x is nan, inf, or already integral */
  62                 if (hx >= 0x7ff00000)        /* x is inf or nan */
  63 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  64                         return (hx >= 0x7ff80000 ? x : x + x);
  65 
  66                 /* assumes sparc-like QNaN */
  67 #else
  68                         return (x + x);
  69 #endif
  70                 return (x);
  71         } else if ((hx | xx.i[LOWORD]) == 0) {  /* x is zero */
  72                 return (x);
  73         }
  74 
  75         /* get the rounding mode */
  76         rm = fegetround();
  77 
  78         /* flip the sense of directed roundings if x is negative */
  79         if (sx && (rm == FE_UPWARD || rm == FE_DOWNWARD))
  80                 rm = (FE_UPWARD + FE_DOWNWARD) - rm;
  81 
  82         /* handle |x| < 1 */
  83         if (hx < 0x3ff00000) {
  84                 if (rm == FE_UPWARD || (rm == FE_TONEAREST && (hx >=
  85                     0x3fe00000 && ((hx & 0xfffff) | xx.i[LOWORD]))))
  86                         xx.i[HIWORD] = sx | 0x3ff00000;
  87                 else
  88                         xx.i[HIWORD] = sx;
  89 
  90                 xx.i[LOWORD] = 0;
  91                 return (xx.d);
  92         }
  93 
  94         /* round x at the integer bit */
  95         j = 0x433 - (hx >> 20);
  96 
  97         if (j >= 32) {
  98                 i = 1 << (j - 32);
  99                 frac = ((xx.i[HIWORD] << 1) << (63 - j)) | (xx.i[LOWORD] >> (j -
 100                     32));
 101 
 102                 if (xx.i[LOWORD] & (i - 1))
 103                         frac |= 1;
 104 
 105                 if (!frac)
 106                         return (x);
 107 
 108                 xx.i[LOWORD] = 0;
 109                 xx.i[HIWORD] &= ~(i - 1);
 110 
 111                 if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) && ((frac >
 112                     0x80000000u) || ((frac == 0x80000000) && (xx.i[HIWORD] &
 113                     i)))))
 114                         xx.i[HIWORD] += i;
 115         } else {
 116                 i = 1 << j;
 117                 frac = (xx.i[LOWORD] << 1) << (31 - j);
 118 
 119                 if (!frac)
 120                         return (x);
 121 
 122                 xx.i[LOWORD] &= ~(i - 1);
 123 
 124                 if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) && (frac >
 125                     0x80000000u || ((frac == 0x80000000) && (xx.i[LOWORD] &
 126                     i))))) {
 127                         xx.i[LOWORD] += i;
 128 
 129                         if (xx.i[LOWORD] == 0)
 130                                 xx.i[HIWORD]++;
 131                 }
 132         }
 133 
 134         return (xx.d);
 135 }