5980be9b3c
This work is based in part on code from NetBSD libm, libc and kernel. The library is partly public domain and partly BSD-style licensed.
107 lines
3.1 KiB
C
107 lines
3.1 KiB
C
/* $NetBSD: s_scalbnl.c,v 1.1 2011/07/26 16:10:16 joerg Exp $ */
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/*-
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* Copyright (c) 2011 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Joerg Sonnenberger.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__RCSID("$NetBSD: s_scalbnl.c,v 1.1 2011/07/26 16:10:16 joerg Exp $");
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#include "namespace.h"
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#include <float.h>
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#include <math.h>
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#include <machine/ieee.h>
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#ifdef __HAVE_LONG_DOUBLE
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#ifdef __weak_alias
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__weak_alias(scalbnl, _scalbnl)
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#endif
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#if LDBL_MANT_DIG == 64
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#define FROM_UNDERFLOW 0x1p65L
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#define TO_UNDERFLOW 0x1p-65L
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#elif LDBL_MANT_DIG == 113
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#define FROM_UNDERFLOW 0x1p114L
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#define TO_UNDERFLOW 0x1p-114L
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#else
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#error Unsupported long double format
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#endif
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long double
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scalbnl(long double x, int n)
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{
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union ieee_ext_u u;
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/* Trivial cases first */
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if (n == 0 || x == 0.0L)
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return x;
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u.extu_ld = x;
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/* NaN and infinite don't change either, but trigger exception */
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if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
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return x + x;
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/* Protect against integer overflow in calculation of new exponent */
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if (n > LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG)
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goto overflow;
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if (n < LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG)
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goto underflow;
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/* Scale denormalized numbers slightly, so that they are normal */
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if (u.extu_ext.ext_exp == 0) {
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u.extu_ld *= FROM_UNDERFLOW;
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n -= LDBL_MANT_DIG + 1;
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}
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n += u.extu_ext.ext_exp;
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if (n >= LDBL_MAX_EXP + EXT_EXP_BIAS)
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goto overflow;
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/* Positive exponent (incl. bias) means normal result */
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if (n > 0) {
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u.extu_ext.ext_exp = n;
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return u.extu_ld;
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}
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/* Shift the exponent and let the multiply below handle subnormal */
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n += LDBL_MANT_DIG + 1;
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if (n <= 0)
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goto underflow;
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u.extu_ext.ext_exp = n;
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return u.extu_ld * TO_UNDERFLOW;
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underflow:
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return LDBL_MIN * copysignl(LDBL_MIN, x);
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overflow:
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return LDBL_MAX * copysignl(LDBL_MAX, x);
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}
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#endif
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