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 __scalbnf = scalbnf
  32 
  33 #include "libm.h"
  34 #include <float.h>                        /* FLT_MAX, FLT_MIN */
  35 #include <stdlib.h>                       /* abs */
  36 
  37 static const float twom25f = 2.98023223876953125e-8F;
  38 
  39 #if defined(__x86)
  40 static const float two23f = 8388608.0F;
  41 #else
  42 /*
  43  * v: a non-zero subnormal |x|; returns [-22, 0]
  44  */
  45 static int
  46 ilogbf_biased(unsigned v)
  47 {
  48         int r = -22;
  49 
  50         if (v & 0xffff0000)
  51                 r += 16, v >>= 16;
  52 
  53         if (v & 0xff00)
  54                 r += 8, v >>= 8;
  55 
  56         if (v & 0xf0)
  57                 r += 4, v >>= 4;
  58 
  59         v <<= 1;
  60         return (r + ((0xffffaa50 >> v) & 0x3));
  61 }
  62 #endif /* defined(__x86) */
  63 
  64 float
  65 scalbnf(float x, int n)
  66 {
  67         int *px = (int *)&x, ix, k;
  68 
  69         ix = *px & ~0x80000000;
  70         k = ix >> 23;
  71 
  72         if (k == 0xff)
  73 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
  74                 return (ix > 0x7f800000 ? x * x : x);
  75 #else
  76                 return (x + x);
  77 #endif
  78 
  79         if (ix == 0 || n == 0)
  80                 return (x);
  81 
  82         if (k == 0) {
  83 #if defined(__x86)
  84                 x *= two23f;
  85                 k = ((*px & ~0x80000000) >> 23) - 23;
  86 #else
  87                 k = ilogbf_biased(ix);
  88                 *px = (*px & 0x80000000) | (ix << (-k + 1));
  89 #endif
  90         }
  91 
  92         if ((unsigned)abs(n) >= 131072)      /* cast to unsigned for -2^31 */
  93                 n >>= 1;          /* avoid subsequent integer overflow */
  94 
  95         k += n;
  96 
  97         if (k > 0xfe)
  98                 return (FLT_MAX * copysignf(FLT_MAX, x));
  99 
 100         if (k <= -25)
 101                 return (FLT_MIN * copysignf(FLT_MIN, x));
 102 
 103         if (k > 0) {
 104                 *px = (*px & ~0x7f800000) | (k << 23);
 105                 return (x);
 106         }
 107 
 108         k += 25;
 109         *px = (*px & ~0x7f800000) | (k << 23);
 110         return (x * twom25f);
 111 }