72 lines
2.0 KiB
C
72 lines
2.0 KiB
C
/* @(#)s_scalbn.c 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#ifndef lint
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static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_scalbnl.c,v 1.1 2005/03/07 04:52:58 das Exp $";
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#endif
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/*
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* scalbnl (long double x, int n)
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* scalbnl(x,n) returns x* 2**n computed by exponent
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* manipulation rather than by actually performing an
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* exponentiation or a multiplication.
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*/
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/*
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* We assume that a long double has a 15-bit exponent. On systems
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* where long double is the same as double, scalbnl() is an alias
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* for scalbn(), so we don't use this routine.
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*/
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#include <sys/cdefs.h>
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#include <float.h>
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#include <math.h>
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#include "fpmath.h"
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#if LDBL_MAX_EXP != 0x4000
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#error "Unsupported long double format"
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#endif
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static const long double
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huge = 0x1p16000L,
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tiny = 0x1p-16000L;
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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 IEEEl2bits u;
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int k;
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u.e = x;
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k = u.bits.exp; /* extract exponent */
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if (k==0) { /* 0 or subnormal x */
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if ((u.bits.manh|u.bits.manl)==0) return x; /* +-0 */
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u.e *= 0x1p+128;
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k = u.bits.exp - 128;
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if (n< -50000) return tiny*x; /*underflow*/
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}
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if (k==0x7fff) return x+x; /* NaN or Inf */
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k = k+n;
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if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */
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if (k > 0) /* normal result */
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{u.bits.exp = k; return u.e;}
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if (k <= -128)
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if (n > 50000) /* in case integer overflow in n+k */
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return huge*copysign(huge,x); /*overflow*/
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else return tiny*copysign(tiny,x); /*underflow*/
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k += 128; /* subnormal result */
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u.bits.exp = k;
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return u.e*0x1p-128;
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}
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__strong_reference(scalbnl, ldexpl);
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