usr/src/lib/libm/common/R/logbf.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 __logbf = logbf
  31
  32 #include "libm.h"
  33 #include "xpg6.h"       /* __xpg6 */
  34 #define _C99SUSv3_logb  _C99SUSv3_logb_subnormal_is_like_ilogb
  35
  36 #if defined(__x86)
  37 static const float two25 = 33554432.0F;
  38 #else
  39 /*
  40  * v: a non-zero subnormal |x|
  41  */
  42 static int
  43 ilogbf_subnormal(unsigned v) {
  44         int r = -126 - 23;
  45
  46         if (v & 0xffff0000)
  47                 r += 16, v >>= 16;
  48         if (v & 0xff00)
  49                 r += 8, v >>= 8;
  50         if (v & 0xf0)
  51                 r += 4, v >>= 4;
  52         v <<= 1;
  53         return (r + ((0xffffaa50 >> v) & 0x3));
  54 }
  55 #endif  /* defined(__x86) */
  56
  57 static float
  58 raise_division(float t) {
  59 #pragma STDC FENV_ACCESS ON
  60         static const float zero = 0.0F;
  61         return (t / zero);
  62 }
  63
  64 float
  65 logbf(float x) {
  66         int k = *((int *) &x) & ~0x80000000;
  67
  68         if (k < 0x00800000) {
  69                 if (k == 0)
  70                         return (raise_division(-1.0F));
  71                 else if ((__xpg6 & _C99SUSv3_logb) != 0) {
  72 #if defined(__x86)
  73                         x *= two25;
  74                         return ((float) (((*((int *) &x) & 0x7f800000) >> 23) -
  75                                 152));
  76 #else
  77                         return ((float) ilogbf_subnormal(k));
  78 #endif
  79                 } else
  80                         return (-126.F);
  81         } else if (k < 0x7f800000)
  82                 return ((float) ((k >> 23) - 127));
  83         else
  84                 return (x * x);
  85 }