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      1 /*	$NetBSD: s_scalbnl.c,v 1.9 2013/05/20 19:40:09 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_scalbnl.c,v 1.9 2013/05/20 19:40:09 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 #ifdef _LP64
     44 long double
     45 scalbnl(long double x, int n)
     46 {
     47 	return scalblnl(x, n);
     48 }
     49 #else
     50 __strong_alias(_scalbnl, _scalblnl)
     51 #endif
     52 
     53 __weak_alias(scalbnl, _scalbnl)
     54 __weak_alias(scalblnl, _scalblnl)
     55 __weak_alias(ldexpl, _scalbnl)
     56 
     57 #if LDBL_MANT_DIG == 64
     58 #define	FROM_UNDERFLOW	0x1p65L
     59 #define	TO_UNDERFLOW	0x1p-65L
     60 #elif LDBL_MANT_DIG == 113
     61 #define	FROM_UNDERFLOW	0x1p114L
     62 #define	TO_UNDERFLOW	0x1p-114L
     63 #else
     64 #error Unsupported long double format
     65 #endif
     66 
     67 long double
     68 scalblnl(long double x, long n)
     69 {
     70 	union ieee_ext_u u;
     71 
     72 	/* Trivial cases first */
     73 	if (n == 0 || x == 0.0L)
     74 		return x;
     75 
     76 	u.extu_ld = x;
     77 
     78 	/* NaN and infinite don't change either, but trigger exception */
     79 	if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
     80 		return x + x;
     81 
     82 	/* Protect against integer overflow in calculation of new exponent */
     83 	if (n > LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG)
     84 		goto overflow;
     85 	if (n < LDBL_MIN_EXP - LDBL_MAX_EXP - LDBL_MANT_DIG)
     86 		goto underflow;
     87 
     88 	/* Scale denormalized numbers slightly, so that they are normal */
     89 	if (u.extu_ext.ext_exp == 0) {
     90 		u.extu_ld *= FROM_UNDERFLOW;
     91 		n -= LDBL_MANT_DIG + 1;
     92 	}
     93 
     94 	n += u.extu_ext.ext_exp;
     95 	if (n >= LDBL_MAX_EXP + EXT_EXP_BIAS)
     96 		goto overflow;
     97 	/* Positive exponent (incl. bias) means normal result */
     98 	if (n > 0) {
     99 		u.extu_ext.ext_exp = n;
    100 		return u.extu_ld;
    101 	}
    102 	/* Shift the exponent and let the multiply below handle subnormal */
    103 	n += LDBL_MANT_DIG + 1;
    104 	if (n <= 0)
    105 		goto underflow;
    106 	u.extu_ext.ext_exp = n;
    107 	return u.extu_ld * TO_UNDERFLOW;
    108 
    109 underflow:
    110 	return LDBL_MIN * copysignl(LDBL_MIN, x);
    111 
    112 overflow:
    113 	return LDBL_MAX * copysignl(LDBL_MAX, x);
    114 }
    115 
    116 #endif
    117