dfrem.c

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/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <[email protected]>
 *
 *    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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
/*
 * BEGIN_DESC
 *
 *  File:
 *  @(#)    pa/spmath/dfrem.c       $Revision: 1.1 $
 *
 *  Purpose:
 *  Double Precision Floating-point Remainder
 *
 *  External Interfaces:
 *  dbl_frem(srcptr1,srcptr2,dstptr,status)
 *
 *  Internal Interfaces:
 *
 *  Theory:
 *  <<please update with a overview of the operation of this file>>
 *
 * END_DESC
*/



#include "float.h"
#include "dbl_float.h"

/*
 *  Double Precision Floating-point Remainder
 */

int
dbl_frem (dbl_floating_point * srcptr1, dbl_floating_point * srcptr2,
      dbl_floating_point * dstptr, unsigned int *status)
{
    register unsigned int opnd1p1, opnd1p2, opnd2p1, opnd2p2;
    register unsigned int resultp1, resultp2;
    register int opnd1_exponent, opnd2_exponent, dest_exponent, stepcount;
    register boolean roundup = FALSE;

    Dbl_copyfromptr(srcptr1,opnd1p1,opnd1p2);
    Dbl_copyfromptr(srcptr2,opnd2p1,opnd2p2);
    /*
     * check first operand for NaN's or infinity
     */
    if ((opnd1_exponent = Dbl_exponent(opnd1p1)) == DBL_INFINITY_EXPONENT) {
        if (Dbl_iszero_mantissa(opnd1p1,opnd1p2)) {
            if (Dbl_isnotnan(opnd2p1,opnd2p2)) {
                /* invalid since first operand is infinity */
                if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                                Set_invalidflag();
                                Dbl_makequietnan(resultp1,resultp2);
                Dbl_copytoptr(resultp1,resultp2,dstptr);
                return(NOEXCEPTION);
            }
        }
        else {
                    /*
                     * is NaN; signaling or quiet?
                     */
                    if (Dbl_isone_signaling(opnd1p1)) {
                            /* trap if INVALIDTRAP enabled */
                            if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                            /* make NaN quiet */
                            Set_invalidflag();
                            Dbl_set_quiet(opnd1p1);
                    }
            /* 
             * is second operand a signaling NaN? 
             */
            else if (Dbl_is_signalingnan(opnd2p1)) {
                            /* trap if INVALIDTRAP enabled */
                            if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                            /* make NaN quiet */
                            Set_invalidflag();
                            Dbl_set_quiet(opnd2p1);
                Dbl_copytoptr(opnd2p1,opnd2p2,dstptr);
                        return(NOEXCEPTION);
            }
                    /*
                     * return quiet NaN
                     */
            Dbl_copytoptr(opnd1p1,opnd1p2,dstptr);
                    return(NOEXCEPTION);
        }
    } 
    /*
     * check second operand for NaN's or infinity
     */
    if ((opnd2_exponent = Dbl_exponent(opnd2p1)) == DBL_INFINITY_EXPONENT) {
        if (Dbl_iszero_mantissa(opnd2p1,opnd2p2)) {
            /*
             * return first operand
             */
            Dbl_copytoptr(opnd1p1,opnd1p2,dstptr);
            return(NOEXCEPTION);
        }
                /*
                 * is NaN; signaling or quiet?
                 */
                if (Dbl_isone_signaling(opnd2p1)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        /* make NaN quiet */
                        Set_invalidflag();
                        Dbl_set_quiet(opnd2p1);
                }
                /*
                 * return quiet NaN
                 */
        Dbl_copytoptr(opnd2p1,opnd2p2,dstptr);
                return(NOEXCEPTION);
    }
    /*
     * check second operand for zero
     */
    if (Dbl_iszero_exponentmantissa(opnd2p1,opnd2p2)) {
        /* invalid since second operand is zero */
        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                Set_invalidflag();
                Dbl_makequietnan(resultp1,resultp2);
        Dbl_copytoptr(resultp1,resultp2,dstptr);
        return(NOEXCEPTION);
    }

    /* 
     * get sign of result
     */
    resultp1 = opnd1p1;  

    /* 
     * check for denormalized operands
     */
    if (opnd1_exponent == 0) {
        /* check for zero */
        if (Dbl_iszero_mantissa(opnd1p1,opnd1p2)) {
            Dbl_copytoptr(opnd1p1,opnd1p2,dstptr);
            return(NOEXCEPTION);
        }
        /* normalize, then continue */
        opnd1_exponent = 1;
        Dbl_normalize(opnd1p1,opnd1p2,opnd1_exponent);
    }
    else {
        Dbl_clear_signexponent_set_hidden(opnd1p1);
    }
    if (opnd2_exponent == 0) {
        /* normalize, then continue */
        opnd2_exponent = 1;
        Dbl_normalize(opnd2p1,opnd2p2,opnd2_exponent);
    }
    else {
        Dbl_clear_signexponent_set_hidden(opnd2p1);
    }

    /* find result exponent and divide step loop count */
    dest_exponent = opnd2_exponent - 1;
    stepcount = opnd1_exponent - opnd2_exponent;

    /*
     * check for opnd1/opnd2 < 1
     */
    if (stepcount < 0) {
        /*
         * check for opnd1/opnd2 > 1/2
         *
         * In this case n will round to 1, so 
         *    r = opnd1 - opnd2 
         */
        if (stepcount == -1 && 
            Dbl_isgreaterthan(opnd1p1,opnd1p2,opnd2p1,opnd2p2)) {
            /* set sign */
            Dbl_allp1(resultp1) = ~Dbl_allp1(resultp1);
            /* align opnd2 with opnd1 */
            Dbl_leftshiftby1(opnd2p1,opnd2p2); 
            Dbl_subtract(opnd2p1,opnd2p2,opnd1p1,opnd1p2,
             opnd2p1,opnd2p2);
            /* now normalize */
                    while (Dbl_iszero_hidden(opnd2p1)) {
                            Dbl_leftshiftby1(opnd2p1,opnd2p2);
                            dest_exponent--;
            }
            Dbl_set_exponentmantissa(resultp1,resultp2,opnd2p1,opnd2p2);
            goto testforunderflow;
        }
        /*
         * opnd1/opnd2 <= 1/2
         *
         * In this case n will round to zero, so 
         *    r = opnd1
         */
        Dbl_set_exponentmantissa(resultp1,resultp2,opnd1p1,opnd1p2);
        dest_exponent = opnd1_exponent;
        goto testforunderflow;
    }

    /*
     * Generate result
     *
     * Do iterative subtract until remainder is less than operand 2.
     */
    while (stepcount-- > 0 && (Dbl_allp1(opnd1p1) || Dbl_allp2(opnd1p2))) {
        if (Dbl_isnotlessthan(opnd1p1,opnd1p2,opnd2p1,opnd2p2)) {
            Dbl_subtract(opnd1p1,opnd1p2,opnd2p1,opnd2p2,opnd1p1,opnd1p2);
        }
        Dbl_leftshiftby1(opnd1p1,opnd1p2);
    }
    /*
     * Do last subtract, then determine which way to round if remainder 
     * is exactly 1/2 of opnd2 
     */
    if (Dbl_isnotlessthan(opnd1p1,opnd1p2,opnd2p1,opnd2p2)) {
        Dbl_subtract(opnd1p1,opnd1p2,opnd2p1,opnd2p2,opnd1p1,opnd1p2);
        roundup = TRUE;
    }
    if (stepcount > 0 || Dbl_iszero(opnd1p1,opnd1p2)) {
        /* division is exact, remainder is zero */
        Dbl_setzero_exponentmantissa(resultp1,resultp2);
        Dbl_copytoptr(resultp1,resultp2,dstptr);
        return(NOEXCEPTION);
    }

    /* 
     * Check for cases where opnd1/opnd2 < n 
     *
     * In this case the result's sign will be opposite that of
     * opnd1.  The mantissa also needs some correction.
     */
    Dbl_leftshiftby1(opnd1p1,opnd1p2);
    if (Dbl_isgreaterthan(opnd1p1,opnd1p2,opnd2p1,opnd2p2)) {
        Dbl_invert_sign(resultp1);
        Dbl_leftshiftby1(opnd2p1,opnd2p2);
        Dbl_subtract(opnd2p1,opnd2p2,opnd1p1,opnd1p2,opnd1p1,opnd1p2);
    }
    /* check for remainder being exactly 1/2 of opnd2 */
    else if (Dbl_isequal(opnd1p1,opnd1p2,opnd2p1,opnd2p2) && roundup) { 
        Dbl_invert_sign(resultp1);
    }

    /* normalize result's mantissa */
        while (Dbl_iszero_hidden(opnd1p1)) {
                dest_exponent--;
                Dbl_leftshiftby1(opnd1p1,opnd1p2);
        }
    Dbl_set_exponentmantissa(resultp1,resultp2,opnd1p1,opnd1p2);

        /* 
         * Test for underflow
         */
    testforunderflow:
    if (dest_exponent <= 0) {
                /* trap if UNDERFLOWTRAP enabled */
                if (Is_underflowtrap_enabled()) {
                        /*
                         * Adjust bias of result
                         */
                        Dbl_setwrapped_exponent(resultp1,dest_exponent,unfl);
            /* frem is always exact */
            Dbl_copytoptr(resultp1,resultp2,dstptr);
            return(UNDERFLOWEXCEPTION);
                }
                /*
                 * denormalize result or set to signed zero
                 */
                if (dest_exponent >= (1 - DBL_P)) {
            Dbl_rightshift_exponentmantissa(resultp1,resultp2,
             1-dest_exponent);
                }
                else {
            Dbl_setzero_exponentmantissa(resultp1,resultp2);
        }
    }
    else Dbl_set_exponent(resultp1,dest_exponent);
    Dbl_copytoptr(resultp1,resultp2,dstptr);
    return(NOEXCEPTION);
}