s_scalbn.c

ecos实时嵌入式操作系统

//===========================================================================
//
//      s_scalbn.c
//
//      Part of the standard mathematical function library
//
//===========================================================================
//####ECOSGPLCOPYRIGHTBEGIN####
// -------------------------------------------
// This file is part of eCos, the Embedded Configurable Operating System.
// Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.
//
// eCos is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 2 or (at your option) any later version.
//
// eCos is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License along
// with eCos; if not, write to the Free Software Foundation, Inc.,
// 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
//
// As a special exception, if other files instantiate templates or use macros
// or inline functions from this file, or you compile this file and link it
// with other works to produce a work based on this file, this file does not
// by itself cause the resulting work to be covered by the GNU General Public
// License. However the source code for this file must still be made available
// in accordance with section (3) of the GNU General Public License.
//
// This exception does not invalidate any other reasons why a work based on
// this file might be covered by the GNU General Public License.
//
// Alternative licenses for eCos may be arranged by contacting Red Hat, Inc.
// at http://sources.redhat.com/ecos/ecos-license/
// -------------------------------------------
//####ECOSGPLCOPYRIGHTEND####
//===========================================================================
//#####DESCRIPTIONBEGIN####
//
// Author(s):   jlarmour
// Contributors:  jlarmour
// Date:        1998-02-13
// Purpose:     
// Description: 
// Usage:       
//
//####DESCRIPTIONEND####
//
//===========================================================================

// CONFIGURATION

#include <pkgconf/libm.h>   // Configuration header

// Include the Math library?
#ifdef CYGPKG_LIBM     

// Derived from code with the following copyright


/* @(#)s_scalbn.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/* 
 * scalbn (double x, int n)
 * scalbn(x,n) returns x* 2**n  computed by  exponent  
 * manipulation rather than by actually performing an 
 * exponentiation or a multiplication.
 */

#include "mathincl/fdlibm.h"

static const double
two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
huge   = 1.0e+300,
tiny   = 1.0e-300;

        double scalbn (double x, int n)
{
        int  k,hx,lx;
        hx = CYG_LIBM_HI(x);
        lx = CYG_LIBM_LO(x);
        k = (hx&0x7ff00000)>>20;                /* extract exponent */
        if (k==0) {                             /* 0 or subnormal x */
            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
            x *= two54; 
            hx = CYG_LIBM_HI(x);
            k = ((hx&0x7ff00000)>>20) - 54; 
            if (n< -50000) return tiny*x;       /*underflow*/
            }
        if (k==0x7ff) return x+x;               /* NaN or Inf */
        k = k+n; 
        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
        if (k > 0)                              /* normal result */
            {CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20); return x;}
        if (k <= -54) {
            if (n > 50000)      /* in case integer overflow in n+k */
                return huge*copysign(huge,x);   /*overflow*/
            else return tiny*copysign(tiny,x);  /*underflow*/
        }
        k += 54;                                /* subnormal result */
        CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20);
        return x*twom54;
}

#endif // ifdef CYGPKG_LIBM     

// EOF s_scalbn.c