fcnvff.c

这个linux源代码是很全面的~基本完整了~使用c编译的~由于时间问题我没有亲自测试~但就算用来做参考资料也是非常好的

/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <[e-mail]>
 *
 *    This program 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.
 *
 *    This program 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 this program; if not, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
/*
 * BEGIN_DESC
 *
 *  File:
 *	@(#)	pa/spmath/fcnvff.c		$Revision: 1.1 $
 *
 *  Purpose:
 *	Single Floating-point to Double Floating-point
 *	Double Floating-point to Single Floating-point
 *
 *  External Interfaces:
 *	dbl_to_sgl_fcnvff(srcptr,nullptr,dstptr,status)
 *	sgl_to_dbl_fcnvff(srcptr,nullptr,dstptr,status)
 *
 *  Internal Interfaces:
 *
 *  Theory:
 *	<<please update with a overview of the operation of this file>>
 *
 * END_DESC
*/


#include "float.h"
#include "sgl_float.h"
#include "dbl_float.h"
#include "cnv_float.h"

/*
 *  Single Floating-point to Double Floating-point 
 */
/*ARGSUSED*/
int
sgl_to_dbl_fcnvff(
	    sgl_floating_point *srcptr,
	    unsigned int *nullptr,
	    dbl_floating_point *dstptr,
	    unsigned int *status)
{
	register unsigned int src, resultp1, resultp2;
	register int src_exponent;

	src = *srcptr;
	src_exponent = Sgl_exponent(src);
	Dbl_allp1(resultp1) = Sgl_all(src);  /* set sign of result */
	/* 
 	 * Test for NaN or infinity
 	 */
	if (src_exponent == SGL_INFINITY_EXPONENT) {
		/*
		 * determine if NaN or infinity
		 */
		if (Sgl_iszero_mantissa(src)) {
			/*
			 * is infinity; want to return double infinity
			 */
			Dbl_setinfinity_exponentmantissa(resultp1,resultp2);
			Dbl_copytoptr(resultp1,resultp2,dstptr);
			return(NOEXCEPTION);
		}
		else {
			/* 
			 * is NaN; signaling or quiet?
			 */
			if (Sgl_isone_signaling(src)) {
				/* trap if INVALIDTRAP enabled */
				if (Is_invalidtrap_enabled())
					return(INVALIDEXCEPTION);
				/* make NaN quiet */
				else {
					Set_invalidflag();
					Sgl_set_quiet(src);
				}
			}
			/* 
			 * NaN is quiet, return as double NaN 
			 */
			Dbl_setinfinity_exponent(resultp1);
			Sgl_to_dbl_mantissa(src,resultp1,resultp2);
			Dbl_copytoptr(resultp1,resultp2,dstptr);
			return(NOEXCEPTION);
		}
	}
	/* 
 	 * Test for zero or denormalized
 	 */
	if (src_exponent == 0) {
		/*
		 * determine if zero or denormalized
		 */
		if (Sgl_isnotzero_mantissa(src)) {
			/*
			 * is denormalized; want to normalize
			 */
			Sgl_clear_signexponent(src);
			Sgl_leftshiftby1(src);
			Sgl_normalize(src,src_exponent);
			Sgl_to_dbl_exponent(src_exponent,resultp1);
			Sgl_to_dbl_mantissa(src,resultp1,resultp2);
		}
		else {
			Dbl_setzero_exponentmantissa(resultp1,resultp2);
		}
		Dbl_copytoptr(resultp1,resultp2,dstptr);
		return(NOEXCEPTION);
	}
	/*
	 * No special cases, just complete the conversion
	 */
	Sgl_to_dbl_exponent(src_exponent, resultp1);
	Sgl_to_dbl_mantissa(Sgl_mantissa(src), resultp1,resultp2);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
}

/*
 *  Double Floating-point to Single Floating-point 
 */
/*ARGSUSED*/
int
dbl_to_sgl_fcnvff(
		    dbl_floating_point *srcptr,
		    unsigned int *nullptr,
		    sgl_floating_point *dstptr,
		    unsigned int *status)
{
        register unsigned int srcp1, srcp2, result;
        register int src_exponent, dest_exponent, dest_mantissa;
        register boolean inexact = FALSE, guardbit = FALSE, stickybit = FALSE;
	register boolean lsb_odd = FALSE;
	boolean is_tiny;

	Dbl_copyfromptr(srcptr,srcp1,srcp2);
        src_exponent = Dbl_exponent(srcp1);
	Sgl_all(result) = Dbl_allp1(srcp1);  /* set sign of result */
        /* 
         * Test for NaN or infinity
         */
        if (src_exponent == DBL_INFINITY_EXPONENT) {
                /*
                 * determine if NaN or infinity
                 */
                if (Dbl_iszero_mantissa(srcp1,srcp2)) {
                        /*
                         * is infinity; want to return single infinity
                         */
                        Sgl_setinfinity_exponentmantissa(result);
                        *dstptr = result;
                        return(NOEXCEPTION);
                }
                /* 
                 * is NaN; signaling or quiet?
                 */
                if (Dbl_isone_signaling(srcp1)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        else {
				Set_invalidflag();
                        	/* make NaN quiet */
                        	Dbl_set_quiet(srcp1);
			}
                }
                /* 
                 * NaN is quiet, return as single NaN 
                 */
                Sgl_setinfinity_exponent(result);
		Sgl_set_mantissa(result,Dallp1(srcp1)<<3 | Dallp2(srcp2)>>29);
		if (Sgl_iszero_mantissa(result)) Sgl_set_quiet(result);
                *dstptr = result;
                return(NOEXCEPTION);
        }
        /*
         * Generate result
         */
        Dbl_to_sgl_exponent(src_exponent,dest_exponent);
	if (dest_exponent > 0) {
        	Dbl_to_sgl_mantissa(srcp1,srcp2,dest_mantissa,inexact,guardbit, 
		stickybit,lsb_odd);
	}
	else {
		if (Dbl_iszero_exponentmantissa(srcp1,srcp2)){
			Sgl_setzero_exponentmantissa(result);
			*dstptr = result;
			return(NOEXCEPTION);
		}
                if (Is_underflowtrap_enabled()) {
			Dbl_to_sgl_mantissa(srcp1,srcp2,dest_mantissa,inexact,
			guardbit,stickybit,lsb_odd);
                }
		else {
			/* compute result, determine inexact info,
			 * and set Underflowflag if appropriate
			 */
			Dbl_to_sgl_denormalized(srcp1,srcp2,dest_exponent,
			dest_mantissa,inexact,guardbit,stickybit,lsb_odd,
			is_tiny);
		}
	}
        /* 
         * Now round result if not exact
         */
        if (inexact) {
                switch (Rounding_mode()) {
                        case ROUNDPLUS: 
                                if (Sgl_iszero_sign(result)) dest_mantissa++;
                                break;
                        case ROUNDMINUS: 
                                if (Sgl_isone_sign(result)) dest_mantissa++;
                                break;
                        case ROUNDNEAREST:
                                if (guardbit) {
                                   if (stickybit || lsb_odd) dest_mantissa++;
                                   }
                }
        }
        Sgl_set_exponentmantissa(result,dest_mantissa);

        /*
         * check for mantissa overflow after rounding
         */
        if ((dest_exponent>0 || Is_underflowtrap_enabled()) && 
	    Sgl_isone_hidden(result)) dest_exponent++;

        /* 
         * Test for overflow
         */
        if (dest_exponent >= SGL_INFINITY_EXPONENT) {
                /* trap if OVERFLOWTRAP enabled */
                if (Is_overflowtrap_enabled()) {
                        /* 
                         * Check for gross overflow
                         */
                        if (dest_exponent >= SGL_INFINITY_EXPONENT+SGL_WRAP) 
                        	return(UNIMPLEMENTEDEXCEPTION);
                        
                        /*
                         * Adjust bias of result
                         */
			Sgl_setwrapped_exponent(result,dest_exponent,ovfl);
			*dstptr = result;
			if (inexact) 
			    if (Is_inexacttrap_enabled())
				return(OVERFLOWEXCEPTION|INEXACTEXCEPTION);
			    else Set_inexactflag();
                        return(OVERFLOWEXCEPTION);
                }
                Set_overflowflag();
		inexact = TRUE;
		/* set result to infinity or largest number */
		Sgl_setoverflow(result);
        }
        /* 
         * Test for underflow
         */
        else if (dest_exponent <= 0) {
                /* trap if UNDERFLOWTRAP enabled */
                if (Is_underflowtrap_enabled()) {
                        /* 
                         * Check for gross underflow
                         */
                        if (dest_exponent <= -(SGL_WRAP))
                        	return(UNIMPLEMENTEDEXCEPTION);
                        /*
                         * Adjust bias of result
                         */
			Sgl_setwrapped_exponent(result,dest_exponent,unfl);
			*dstptr = result;
			if (inexact) 
			    if (Is_inexacttrap_enabled())
				return(UNDERFLOWEXCEPTION|INEXACTEXCEPTION);
			    else Set_inexactflag();
                        return(UNDERFLOWEXCEPTION);
                }
                 /* 
                  * result is denormalized or signed zero
                  */
               if (inexact && is_tiny) Set_underflowflag();

        }
	else Sgl_set_exponent(result,dest_exponent);
	*dstptr = result;
        /* 
         * Trap if inexact trap is enabled
         */
        if (inexact)
        	if (Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
        	else Set_inexactflag();
        return(NOEXCEPTION);
}