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 __scalbln = scalbln
  31 
  32 #include "libm.h"
  33 #include <float.h>                /* DBL_MAX, DBL_MIN */
  34 
  35 static const double twom54 = 5.5511151231257827021181583404541015625e-17;
  36 #if defined(__x86)
  37 static const double two52 = 4503599627370496.0;
  38 #else
  39 /*
  40  * Normalize non-zero subnormal x and return biased exponent of x in [-51,0]
  41  */
  42 static int
  43 ilogb_biased(unsigned *px) {
  44         int s = 52;
  45         unsigned v = px[HIWORD] & ~0x80000000, w = px[LOWORD], t = v;
  46 
  47         if (t)
  48                 s -= 32;
  49         else
  50                 t = w;
  51         if (t & 0xffff0000)
  52                 s -= 16, t >>= 16;
  53         if (t & 0xff00)
  54                 s -= 8, t >>= 8;
  55         if (t & 0xf0)
  56                 s -= 4, t >>= 4;
  57         t <<= 1;
  58         s -= (0xffffaa50 >> t) & 0x3;
  59         if (s < 32) {
  60                 v = (v << s) | w >> (32 - s);
  61                 w <<= s;
  62         } else {
  63                 v = w << (s - 32);
  64                 w = 0;
  65         }
  66         px[HIWORD] = (px[HIWORD] & 0x80000000) | v;
  67         px[LOWORD] = w;
  68         return (1 - s);
  69 }
  70 #endif  /* defined(__x86) */
  71 
  72 double
  73 scalbln(double x, long n) {
  74         int *px = (int *) &x, ix, k;
  75 
  76         ix = px[HIWORD] & ~0x80000000;
  77         k = ix >> 20;
  78         if (k == 0x7ff)
  79 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  80                 return ((px[HIWORD] & 0x80000) != 0 ? x : x + x);
  81                 /* assumes sparc-like QNaN */
  82 #else
  83                 return (x + x);
  84 #endif
  85         if ((px[LOWORD] | ix) == 0 || n == 0)
  86                 return (x);
  87         if (k == 0) {
  88 #if defined(__x86)
  89                 x *= two52;
  90                 k = ((px[HIWORD] & ~0x80000000) >> 20) - 52;
  91 #else
  92                 k = ilogb_biased((unsigned *) px);
  93 #endif
  94         }
  95         k += (int) n;
  96         if (n > 5000 || k > 0x7fe)
  97                 return (DBL_MAX * copysign(DBL_MAX, x));
  98         if (n < -5000 || k <= -54)
  99                 return (DBL_MIN * copysign(DBL_MIN, x));
 100         if (k > 0) {
 101                 px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 102                 return (x);
 103         }
 104         k += 54;
 105         px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 106         return (x * twom54);
 107 }