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 __scalbln = scalbln
  32 
  33 #include "libm.h"
  34 #include <float.h>                        /* DBL_MAX, DBL_MIN */
  35 
  36 static const double twom54 = 5.5511151231257827021181583404541015625e-17;
  37 
  38 #if defined(__x86)
  39 static const double two52 = 4503599627370496.0;
  40 #else
  41 /*
  42  * Normalize non-zero subnormal x and return biased exponent of x in [-51,0]
  43  */
  44 static int
  45 ilogb_biased(unsigned *px)
  46 {
  47         int s = 52;
  48         unsigned v = px[HIWORD] & ~0x80000000, w = px[LOWORD], t = v;
  49 
  50         if (t)
  51                 s -= 32;
  52         else
  53                 t = w;
  54 
  55         if (t & 0xffff0000)
  56                 s -= 16, t >>= 16;
  57 
  58         if (t & 0xff00)
  59                 s -= 8, t >>= 8;
  60 
  61         if (t & 0xf0)
  62                 s -= 4, t >>= 4;
  63 
  64         t <<= 1;
  65         s -= (0xffffaa50 >> t) & 0x3;
  66 
  67         if (s < 32) {
  68                 v = (v << s) | w >> (32 - s);
  69                 w <<= s;
  70         } else {
  71                 v = w << (s - 32);
  72                 w = 0;
  73         }
  74 
  75         px[HIWORD] = (px[HIWORD] & 0x80000000) | v;
  76         px[LOWORD] = w;
  77         return (1 - s);
  78 }
  79 #endif /* defined(__x86) */
  80 
  81 double
  82 scalbln(double x, long n)
  83 {
  84         int *px = (int *)&x, ix, k;
  85 
  86         ix = px[HIWORD] & ~0x80000000;
  87         k = ix >> 20;
  88 
  89         if (k == 0x7ff)
  90 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  91                 return ((px[HIWORD] & 0x80000) != 0 ? x : x + x);
  92 
  93         /* assumes sparc-like QNaN */
  94 #else
  95                 return (x + x);
  96 #endif
  97 
  98         if ((px[LOWORD] | ix) == 0 || n == 0)
  99                 return (x);
 100 
 101         if (k == 0) {
 102 #if defined(__x86)
 103                 x *= two52;
 104                 k = ((px[HIWORD] & ~0x80000000) >> 20) - 52;
 105 #else
 106                 k = ilogb_biased((unsigned *)px);
 107 #endif
 108         }
 109 
 110         k += (int)n;
 111 
 112         if (n > 5000 || k > 0x7fe)
 113                 return (DBL_MAX * copysign(DBL_MAX, x));
 114 
 115         if (n < -5000 || k <= -54)
 116                 return (DBL_MIN * copysign(DBL_MIN, x));
 117 
 118         if (k > 0) {
 119                 px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 120                 return (x);
 121         }
 122 
 123         k += 54;
 124         px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 125         return (x * twom54);
 126 }