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1 56 joel
 
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/* @(#)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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/*
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FUNCTION
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<<scalbn>>, <<scalbnf>>---scale by integer
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INDEX
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        scalbn
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INDEX
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        scalbnf
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ANSI_SYNOPSIS
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        #include <math.h>
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        double scalbn(double <[x]>, int <[y]>);
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        float scalbnf(float <[x]>, int <[y]>);
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TRAD_SYNOPSIS
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        #include <math.h>
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        double scalbn(<[x]>,<[y]>)
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        double <[x]>;
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        int <[y]>;
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        float scalbnf(<[x]>,<[y]>)
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        float <[x]>;
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        int <[y]>;
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DESCRIPTION
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<<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times
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2 to the power <[n]>.  The result is computed by manipulating the
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exponent, rather than by actually performing an exponentiation or
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multiplication.
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RETURNS
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<[x]> times 2 to the power <[n]>.
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PORTABILITY
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Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V
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Interface Definition (Issue 2).
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*/
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/*
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 * scalbn (double x, int n)
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 * scalbn(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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#include "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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huge   = 1.0e+300,
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tiny   = 1.0e-300;
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#ifdef __STDC__
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        double scalbn (double x, int n)
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#else
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        double scalbn (x,n)
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        double x; int n;
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#endif
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{
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        __int32_t  k,hx,lx;
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        EXTRACT_WORDS(hx,lx,x);
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        k = (hx&0x7ff00000)>>20;                /* extract exponent */
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        if (k==0) {                              /* 0 or subnormal x */
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            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
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            x *= two54;
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            GET_HIGH_WORD(hx,x);
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            k = ((hx&0x7ff00000)>>20) - 54;
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            if (n< -50000) return tiny*x;       /*underflow*/
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            }
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        if (k==0x7ff) return x+x;               /* NaN or Inf */
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        k = k+n;
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        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
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        if (k > 0)                               /* normal result */
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            {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
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        if (k <= -54)
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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 += 54;                                /* subnormal result */
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        SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
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        return x*twom54;
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}
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#endif /* _DOUBLE_IS_32BITS */

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