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 #if defined(ELFOBJ)
  31 #pragma weak scalbln = __scalbln
  32 #endif
  33 
  34 #include "libm.h"
  35 #include <float.h>                /* DBL_MAX, DBL_MIN */
  36 
  37 static const double twom54 = 5.5511151231257827021181583404541015625e-17;
  38 #if defined(USE_FPSCALE) || 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         int s = 52;
  47         unsigned v = px[HIWORD] & ~0x80000000, w = px[LOWORD], t = v;
  48 
  49         if (t)
  50                 s -= 32;
  51         else
  52                 t = w;
  53         if (t & 0xffff0000)
  54                 s -= 16, t >>= 16;
  55         if (t & 0xff00)
  56                 s -= 8, t >>= 8;
  57         if (t & 0xf0)
  58                 s -= 4, t >>= 4;
  59         t <<= 1;
  60         s -= (0xffffaa50 >> t) & 0x3;
  61         if (s < 32) {
  62                 v = (v << s) | w >> (32 - s);
  63                 w <<= s;
  64         } else {
  65                 v = w << (s - 32);
  66                 w = 0;
  67         }
  68         px[HIWORD] = (px[HIWORD] & 0x80000000) | v;
  69         px[LOWORD] = w;
  70         return (1 - s);
  71 }
  72 #endif  /* defined(USE_FPSCALE) */
  73 
  74 double
  75 scalbln(double x, long n) {
  76         int *px = (int *) &x, ix, k;
  77 
  78         ix = px[HIWORD] & ~0x80000000;
  79         k = ix >> 20;
  80         if (k == 0x7ff)
  81 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  82                 return ((px[HIWORD] & 0x80000) != 0 ? x : x + x);
  83                 /* assumes sparc-like QNaN */
  84 #else
  85                 return (x + x);
  86 #endif
  87         if ((px[LOWORD] | ix) == 0 || n == 0)
  88                 return (x);
  89         if (k == 0) {
  90 #if defined(USE_FPSCALE) || defined(__x86)
  91                 x *= two52;
  92                 k = ((px[HIWORD] & ~0x80000000) >> 20) - 52;
  93 #else
  94                 k = ilogb_biased((unsigned *) px);
  95 #endif
  96         }
  97         k += (int) n;
  98         if (n > 5000 || k > 0x7fe)
  99                 return (DBL_MAX * copysign(DBL_MAX, x));
 100         if (n < -5000 || k <= -54)
 101                 return (DBL_MIN * copysign(DBL_MIN, x));
 102         if (k > 0) {
 103                 px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 104                 return (x);
 105         }
 106         k += 54;
 107         px[HIWORD] = (px[HIWORD] & ~0x7ff00000) | (k << 20);
 108         return (x * twom54);
 109 }