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