usr/src/lib/libm/common/C/nextafter.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 2005 Sun Microsystems, Inc.  All rights reserved.
  26  * Use is subject to license terms.
  27  */
  28
  29 #pragma weak __nextafter = nextafter
  30 #pragma weak _nextafter = nextafter
  31
  32 #include "libm.h"
  33 #include <float.h>              /* DBL_MIN */
  34
  35 double
  36 nextafter(double x, double y) {
  37         int             hx, hy, k;
  38         double          ans;
  39         unsigned        lx;
  40         volatile double dummy __unused;
  41
  42         hx = ((int *)&x)[HIWORD];
  43         lx = ((int *)&x)[LOWORD];
  44         hy = ((int *)&y)[HIWORD];
  45         k = (hx & ~0x80000000) | lx;
  46
  47         if (x == y)
  48                 return (y);             /* C99 requirement */
  49         if (x != x || y != y)
  50                 return (x * y);
  51         if (k == 0) {                   /* x = 0 */
  52                 k = hy & 0x80000000;
  53                 ((int *)&ans)[HIWORD] = k;
  54                 ((int *)&ans)[LOWORD] = 1;
  55         } else if (hx >= 0) {
  56                 if (x > y) {
  57                         ((int *)&ans)[LOWORD] = lx - 1;
  58                         k = (lx == 0)? hx - 1 : hx;
  59                         ((int *)&ans)[HIWORD] = k;
  60                 } else {
  61                         ((int *)&ans)[LOWORD] = lx + 1;
  62                         k  = (lx == 0xffffffff)? hx + 1 : hx;
  63                         ((int *)&ans)[HIWORD] = k;
  64                 }
  65         } else {
  66                 if (x < y) {
  67                         ((int *)&ans)[LOWORD] = lx - 1;
  68                         k = (lx == 0)? hx - 1 : hx;
  69                         ((int *)&ans)[HIWORD] = k;
  70                 } else {
  71                         ((int *)&ans)[LOWORD] = lx + 1;
  72                         k  = (lx == 0xffffffff)? hx + 1 : hx;
  73                         ((int *)&ans)[HIWORD] = k;
  74                 }
  75         }
  76         k = (k >> 20) & 0x7ff;
  77         if (k == 0x7ff) {
  78                 /* overflow */
  79                 return (_SVID_libm_err(x, y, 46));
  80         } else if (k == 0) {
  81                 /* underflow */
  82                 dummy = DBL_MIN * copysign(DBL_MIN, x);
  83         }
  84         return (ans);
  85 }