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 __logbl = logbl
  32 
  33 #include "libm.h"
  34 #include "xpg6.h"                       /* __xpg6 */
  35 #define _C99SUSv3_logb          _C99SUSv3_logb_subnormal_is_like_ilogb
  36 
  37 #if defined(__sparc)
  38 #define ISNORMALL(k, x)         (k != 0x7fff)   /* assuming k != 0 */
  39 #define X86PDNRM(k, x)
  40 #define XSCALE_OFFSET           0x406f          /* 0x3fff + 112 */
  41 
  42 static const long double xscale = 5192296858534827628530496329220096.0L;
  43 
  44 /* 2^112 */
  45 #elif defined(__x86)
  46 /*
  47  * if pseudo-denormal, replace by the equivalent normal
  48  */
  49 #define X86PDNRM(k, x)  \
  50         if (k == 0 && (((int *)&x)[1] & 0x80000000) !=  0) \
  51                 ((int *)&x)[2] |= k = 1
  52 #if defined(HANDLE_UNSUPPORTED)         /* assuming k != 0 */
  53 #define ISNORMALL(k, x) (k != 0x7fff && (((int *)&x)[1] & 0x80000000) != \
  54         0)
  55 #else
  56 #define ISNORMALL(k, x) (k != 0x7fff)
  57 #endif
  58 #define XSCALE_OFFSET   0x403e                          /* 0x3fff + 63 */
  59 static const long double xscale = 9223372036854775808.0L;       /* 2^63 */
  60 #endif
  61 
  62 static long double
  63 raise_division(long double v)
  64 {
  65 #pragma STDC FENV_ACCESS ON
  66 
  67         static const long double zero = 0.0L;
  68 
  69         return (v / zero);
  70 }
  71 
  72 long double
  73 logbl(long double x)
  74 {
  75         int k = XBIASED_EXP(x);
  76 
  77         X86PDNRM(k, x);
  78 
  79         if (k == 0) {
  80                 if (ISZEROL(x)) {
  81                         return (raise_division(-1.0L));
  82                 } else if ((__xpg6 & _C99SUSv3_logb) != 0) {
  83                         x *= xscale;    /* scale up by 2^112 or 2^63 */
  84                         return ((long double)(XBIASED_EXP(x) - XSCALE_OFFSET));
  85                 } else {
  86                         return (-16382.L);
  87                 }
  88         } else if (ISNORMALL(k, x)) {
  89                 return ((long double)(k - 0x3fff));
  90         } else {
  91                 return (x * x);
  92         }
  93 }