/*      $NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $       */

/*
* Copyright (c) 1995  Ken Nakata
*      All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
* 3. Neither the name of the author nor the names of its contributors
*    may be used to endorse or promote products derived from this software
*    without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*      @(#)fpu_rem.c   10/24/95
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $");

#include <sys/types.h>
#include <sys/signal.h>
#include <machine/frame.h>

#include "fpu_emulate.h"

/*
*       ALGORITHM
*
*       Step 1.  Save and strip signs of X and Y: signX := sign(X),
*                signY := sign(Y), X := *X*, Y := *Y*,
*                signQ := signX EOR signY. Record whether MOD or REM
*                is requested.
*
*       Step 2.  Set L := expo(X)-expo(Y), Q := 0.
*                If (L < 0) then
*                   R := X, go to Step 4.
*                else
*                   R := 2^(-L)X, j := L.
*                endif
*
*       Step 3.  Perform MOD(X,Y)
*            3.1 If R = Y, then { Q := Q + 1, R := 0, go to Step 7. }
*            3.2 If R > Y, then { R := R - Y, Q := Q + 1}
*            3.3 If j = 0, go to Step 4.
*            3.4 j := j - 1, Q := 2Q, R := 2R. Go to Step 3.1.
*
*       Step 4.  R := signX*R.
*
*       Step 5.  If MOD is requested, go to Step 7.
*
*       Step 6.  Now, R = MOD(X,Y), convert to REM(X,Y) is requested.
*                Do banker's rounding.
*                If   abs(R) > Y/2
*                 || (abs(R) == Y/2 && Q % 2 == 1) then
*                 { Q := Q + 1, R := R - signX * Y }.
*
*       Step 7.  Return signQ, last 7 bits of Q, and R as required.
*/

static struct fpn * __fpu_modrem(struct fpemu *fe, int is_mod);
static int abscmp3(const struct fpn *a, const struct fpn *b);

/* Absolute FORTRAN Compare */
static int
abscmp3(const struct fpn *a, const struct fpn *b)
{
       int i;

       if (a->fp_exp < b->fp_exp) {
               return -1;
       } else if (a->fp_exp > b->fp_exp) {
               return 1;
       } else {
               for (i = 0; i < 3; i++) {
                       if (a->fp_mant[i] < b->fp_mant[i])
                               return -1;
                       else if (a->fp_mant[i] > b->fp_mant[i])
                               return 1;
               }
       }
       return 0;
}

static struct fpn *
__fpu_modrem(struct fpemu *fe, int is_mod)
{
       static struct fpn X, Y;
       struct fpn *x, *y, *r;
       uint32_t signX, signY, signQ;
       int j, l, q;
       int cmp;

       if (ISNAN(&fe->fe_f1) || ISNAN(&fe->fe_f2))
               return fpu_newnan(fe);
       if (ISINF(&fe->fe_f1) || ISZERO(&fe->fe_f2))
               return fpu_newnan(fe);

       CPYFPN(&X, &fe->fe_f1);
       CPYFPN(&Y, &fe->fe_f2);
       x = &X;
       y = &Y;
       q = 0;
       r = &fe->fe_f2;

       /*
        * Step 1
        */
       signX = x->fp_sign;
       signY = y->fp_sign;
       signQ = (signX ^ signY);
       x->fp_sign = y->fp_sign = 0;

       /* Special treatment that just return input value but Q is necessary */
       if (ISZERO(x) || ISINF(y)) {
               r = &fe->fe_f1;
               goto Step7;
       }

       /*
        * Step 2
        */
       l = x->fp_exp - y->fp_exp;
       CPYFPN(r, x);
       if (l >= 0) {
               r->fp_exp -= l;
               j = l;

               /*
                * Step 3
                */
               for (;;) {
                       cmp = abscmp3(r, y);

                       /* Step 3.1 */
                       if (cmp == 0)
                               break;

                       /* Step 3.2 */
                       if (cmp > 0) {
                               CPYFPN(&fe->fe_f1, r);
                               CPYFPN(&fe->fe_f2, y);
                               fe->fe_f2.fp_sign = 1;
                               r = fpu_add(fe);
                               q++;
                       }

                       /* Step 3.3 */
                       if (j == 0)
                               goto Step4;

                       /* Step 3.4 */
                       j--;
                       q += q;
                       r->fp_exp++;
               }
               /* R == Y */
               q++;
               r->fp_class = FPC_ZERO;
               goto Step7;
       }
Step4:
       r->fp_sign = signX;

       /*
        * Step 5
        */
       if (is_mod)
               goto Step7;

       /*
        * Step 6
        */
       /* y = y / 2 */
       y->fp_exp--;
       /* abscmp3 ignore sign */
       cmp = abscmp3(r, y);
       /* revert y */
       y->fp_exp++;

       if (cmp > 0 || (cmp == 0 && q % 2)) {
               q++;
               CPYFPN(&fe->fe_f1, r);
               CPYFPN(&fe->fe_f2, y);
               fe->fe_f2.fp_sign = !signX;
               r = fpu_add(fe);
       }

       /*
        * Step 7
        */
Step7:
       q &= 0x7f;
       q |= (signQ << 7);
       fe->fe_fpframe->fpf_fpsr =
       fe->fe_fpsr =
           (fe->fe_fpsr & ~FPSR_QTT) | (q << 16);
       return r;
}

struct fpn *
fpu_rem(struct fpemu *fe)
{
       return __fpu_modrem(fe, 0);
}

struct fpn *
fpu_mod(struct fpemu *fe)
{
       return __fpu_modrem(fe, 1);
}

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