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      1 /* $NetBSD: compat_frexp_ieee754.c,v 1.6 2024/01/20 14:52:45 christos Exp $ */
      2 
      3 /*
      4  * Copyright (c) 1992, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This software was developed by the Computer Systems Engineering group
      8  * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
      9  * contributed to Berkeley.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions and the following disclaimer.
     16  * 2. Redistributions in binary form must reproduce the above copyright
     17  *    notice, this list of conditions and the following disclaimer in the
     18  *    documentation and/or other materials provided with the distribution.
     19  * 3. Neither the name of the University nor the names of its contributors
     20  *    may be used to endorse or promote products derived from this software
     21  *    without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     33  * SUCH DAMAGE.
     34  *
     35  * from: Header: frexp.c,v 1.1 91/07/07 04:45:01 torek Exp
     36  */
     37 
     38 #include <sys/cdefs.h>
     39 #if defined(LIBC_SCCS) && !defined(lint)
     40 #if 0
     41 static char sccsid[] = "@(#)frexp.c	8.1 (Berkeley) 6/4/93";
     42 #else
     43 __RCSID("$NetBSD: compat_frexp_ieee754.c,v 1.6 2024/01/20 14:52:45 christos Exp $");
     44 #endif
     45 #endif /* LIBC_SCCS and not lint */
     46 
     47 #include <sys/types.h>
     48 #include <machine/ieee.h>
     49 #include <math.h>
     50 
     51 /*
     52  * Split the given value into a fraction in the range [0.5, 1.0) and
     53  * an exponent, such that frac * (2^exp) == value.  If value is 0,
     54  * return 0.
     55  */
     56 double
     57 frexp(double value, int *eptr)
     58 {
     59 	union ieee_double_u u;
     60 
     61 	if (value) {
     62 		/*
     63 		 * Fractions in [0.5..1.0) have an exponent of 2^-1.
     64 		 * Leave Inf and NaN alone, however.
     65 		 */
     66 		u.dblu_d = value;
     67 		if (u.dblu_dbl.dbl_exp != DBL_EXP_INFNAN) {
     68 			*eptr = 0;
     69 			if (u.dblu_dbl.dbl_exp == 0) {
     70 				/* denormal, scale out of mantissa */
     71 				*eptr = -DBL_FRACBITS;
     72 				u.dblu_d *= 4.50359962737049600000e+15;
     73 			}
     74 			*eptr += u.dblu_dbl.dbl_exp - (DBL_EXP_BIAS - 1);
     75 			u.dblu_dbl.dbl_exp = DBL_EXP_BIAS - 1;
     76 		}
     77 		return (u.dblu_d);
     78 	} else {
     79 		*eptr = 0;
     80 		return (value);
     81 	}
     82 }
     83