usr/src/lib/libm/common/LD/logbl.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 __logbl = logbl
  31
  32 #include "libm.h"
  33 #include "xpg6.h"       /* __xpg6 */
  34 #define _C99SUSv3_logb  _C99SUSv3_logb_subnormal_is_like_ilogb
  35
  36 #if defined(__sparc)
  37 #define ISNORMALL(k, x) (k != 0x7fff)                   /* assuming k != 0 */
  38 #define X86PDNRM(k, x)
  39 #define XSCALE_OFFSET   0x406f                          /* 0x3fff + 112 */
  40 static const long double xscale = 5192296858534827628530496329220096.0L;
  41                                                                 /* 2^112 */
  42 #elif defined(__x86)
  43 /*
  44  * if pseudo-denormal, replace by the equivalent normal
  45  */
  46 #define X86PDNRM(k, x)  if (k == 0 && (((int *) &x)[1] & 0x80000000) != 0) \
  47                                 ((int *) &x)[2] |= k = 1
  48 #if defined(HANDLE_UNSUPPORTED)                         /* assuming k != 0 */
  49 #define ISNORMALL(k, x) (k != 0x7fff && (((int *) &x)[1] & 0x80000000) != 0)
  50 #else
  51 #define ISNORMALL(k, x) (k != 0x7fff)
  52 #endif
  53 #define XSCALE_OFFSET   0x403e                          /* 0x3fff + 63 */
  54 static const long double xscale = 9223372036854775808.0L;       /* 2^63 */
  55 #endif
  56
  57 static long double
  58 raise_division(long double v) {
  59 #pragma STDC FENV_ACCESS ON
  60         static const long double zero = 0.0L;
  61         return (v / zero);
  62 }
  63
  64 long double
  65 logbl(long double x) {
  66         int k = XBIASED_EXP(x);
  67
  68         X86PDNRM(k, x);
  69         if (k == 0) {
  70                 if (ISZEROL(x))
  71                         return (raise_division(-1.0L));
  72                 else if ((__xpg6 & _C99SUSv3_logb) != 0) {
  73                         x *= xscale;            /* scale up by 2^112 or 2^63 */
  74                         return (long double) (XBIASED_EXP(x) - XSCALE_OFFSET);
  75                 } else
  76                         return ((long double) (-16382));
  77         } else if (ISNORMALL(k, x))
  78                 return ((long double) (k - 0x3fff));
  79         else
  80                 return (x * x);
  81 }