lib/libm/src/s_logbl.c

   1 /*      $NetBSD: s_logbl.c,v 1.1 2011/08/03 14:13:07 joerg Exp $        */
   2
   3 /*-
   4  * Copyright (c) 2011 The NetBSD Foundation, Inc.
   5  * All rights reserved.
   6  *
   7  * This code is derived from software contributed to The NetBSD Foundation
   8  * by Joerg Sonnenberger.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
  20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
  23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  29  * POSSIBILITY OF SUCH DAMAGE.
  30  */
  31
  32 #include <sys/cdefs.h>
  33 __RCSID("$NetBSD: s_logbl.c,v 1.1 2011/08/03 14:13:07 joerg Exp $");
  34
  35 #include "namespace.h"
  36
  37 #include <float.h>
  38 #include <math.h>
  39 #include <machine/ieee.h>
  40
  41 #ifdef __HAVE_LONG_DOUBLE
  42
  43 #if LDBL_MANT_DIG == 64
  44 #define FROM_UNDERFLOW  0x1p65L
  45 #elif LDBL_MANT_DIG == 113
  46 #define FROM_UNDERFLOW  0x1p114L
  47 #else
  48 #error Unsupported long double format
  49 #endif
  50
  51 long double
  52 logbl(long double x)
  53 {
  54         union ieee_ext_u u;
  55
  56         if (x == 0.0L)
  57                 return -1.0L / fabsl(x); /* -HUGE_VALL + exception */
  58
  59         u.extu_ld = x;
  60
  61         if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
  62                 return fabsl(x); /* NaN or +Inf */
  63
  64         if (u.extu_ext.ext_exp == 0) {
  65                 /*
  66                  * Scale denormalized numbers slightly,
  67                  * so that they are normal.
  68                  */
  69                 u.extu_ld *= FROM_UNDERFLOW;
  70                 return u.extu_ext.ext_exp - EXT_EXP_BIAS - LDBL_MANT_DIG - 1;
  71         }
  72         return u.extu_ext.ext_exp - EXT_EXP_BIAS;
  73
  74 }
  75
  76 #endif