usr/src/lib/libm/common/m9x/nearbyint.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 /*
  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 #pragma weak nearbyint = __nearbyint
  31
  32 /*
  33  * nearbyint(x) returns the nearest fp integer to x in the direction
  34  * corresponding to the current rounding direction without raising
  35  * the inexact exception.
  36  *
  37  * nearbyint(x) is x unchanged if x is +/-0 or +/-inf.  If x is NaN,
  38  * nearbyint(x) is also NaN.
  39  */
  40
  41 #include "libm.h"
  42 #include <fenv.h>
  43
  44 double
  45 __nearbyint(double x) {
  46         union {
  47                 unsigned i[2];
  48                 double d;
  49         } xx;
  50         unsigned hx, sx, i, frac;
  51         int rm, j;
  52
  53         xx.d = x;
  54         sx = xx.i[HIWORD] & 0x80000000;
  55         hx = xx.i[HIWORD] & ~0x80000000;
  56
  57         /* handle trivial cases */
  58         if (hx >= 0x43300000) { /* x is nan, inf, or already integral */
  59                 if (hx >= 0x7ff00000)   /* x is inf or nan */
  60 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  61                         return (hx >= 0x7ff80000 ? x : x + x);
  62                         /* assumes sparc-like QNaN */
  63 #else
  64                         return (x + x);
  65 #endif
  66                 return (x);
  67         } else if ((hx | xx.i[LOWORD]) == 0)    /* x is zero */
  68                 return (x);
  69
  70         /* get the rounding mode */
  71         rm = fegetround();
  72
  73         /* flip the sense of directed roundings if x is negative */
  74         if (sx && (rm == FE_UPWARD || rm == FE_DOWNWARD))
  75                 rm = (FE_UPWARD + FE_DOWNWARD) - rm;
  76
  77         /* handle |x| < 1 */
  78         if (hx < 0x3ff00000) {
  79                 if (rm == FE_UPWARD || (rm == FE_TONEAREST &&
  80                         (hx >= 0x3fe00000 && ((hx & 0xfffff) | xx.i[LOWORD]))))
  81                         xx.i[HIWORD] = sx | 0x3ff00000;
  82                 else
  83                         xx.i[HIWORD] = sx;
  84                 xx.i[LOWORD] = 0;
  85                 return (xx.d);
  86         }
  87
  88         /* round x at the integer bit */
  89         j = 0x433 - (hx >> 20);
  90         if (j >= 32) {
  91                 i = 1 << (j - 32);
  92                 frac = ((xx.i[HIWORD] << 1) << (63 - j)) |
  93                         (xx.i[LOWORD] >> (j - 32));
  94                 if (xx.i[LOWORD] & (i - 1))
  95                         frac |= 1;
  96                 if (!frac)
  97                         return (x);
  98                 xx.i[LOWORD] = 0;
  99                 xx.i[HIWORD] &= ~(i - 1);
 100                 if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
 101                         ((frac > 0x80000000u) || ((frac == 0x80000000) &&
 102                         (xx.i[HIWORD] & i)))))
 103                         xx.i[HIWORD] += i;
 104         } else {
 105                 i = 1 << j;
 106                 frac = (xx.i[LOWORD] << 1) << (31 - j);
 107                 if (!frac)
 108                         return (x);
 109                 xx.i[LOWORD] &= ~(i - 1);
 110                 if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
 111                         (frac > 0x80000000u || ((frac == 0x80000000) &&
 112                         (xx.i[LOWORD] & i))))) {
 113                         xx.i[LOWORD] += i;
 114                         if (xx.i[LOWORD] == 0)
 115                                 xx.i[HIWORD]++;
 116                 }
 117         }
 118         return (xx.d);
 119 }