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      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
     77