/*      $NetBSD: fpu_subr.c,v 1.9 2022/09/06 23:02:36 rin Exp $ */

/*
* Copyright (c) 1992, 1993
*      The Regents of the University of California.  All rights reserved.
*
* This software was developed by the Computer Systems Engineering group
* at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
* contributed to Berkeley.
*
* All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
*      This product includes software developed by the University of
*      California, Lawrence Berkeley Laboratory.
*
* 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 University 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 REGENTS 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 REGENTS 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_subr.c  8.1 (Berkeley) 6/11/93
*/

/*
* FPU subroutines.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: fpu_subr.c,v 1.9 2022/09/06 23:02:36 rin Exp $");

#include <sys/types.h>
#include <sys/systm.h>

#include <powerpc/instr.h>
#include <machine/fpu.h>
#include <machine/reg.h>

#include <powerpc/fpu/fpu_arith.h>
#include <powerpc/fpu/fpu_emu.h>
#include <powerpc/fpu/fpu_extern.h>

/*
* Shift the given number right rsh bits.  Any bits that `fall off' will get
* shoved into the sticky field; we return the resulting sticky.  Note that
* shifting NaNs is legal (this will never shift all bits out); a NaN's
* sticky field is ignored anyway.
*/
int
fpu_shr(struct fpn *fp, int rsh)
{
       u_int m0, m1, m2, m3, s;
       int lsh;

       KASSERTMSG(rsh > 0 && (fp->fp_class == FPC_NUM || ISNAN(fp)),
           "rsh %d, class %d\n", rsh, fp->fp_class);

       m0 = fp->fp_mant[0];
       m1 = fp->fp_mant[1];
       m2 = fp->fp_mant[2];
       m3 = fp->fp_mant[3];

       /* If shifting all the bits out, take a shortcut. */
       if (rsh >= FP_NMANT) {
               KASSERT((m0 | m1 | m2 | m3) != 0);
               fp->fp_mant[0] = 0;
               fp->fp_mant[1] = 0;
               fp->fp_mant[2] = 0;
               fp->fp_mant[3] = 0;
#ifdef notdef
               if ((m0 | m1 | m2 | m3) == 0)
                       fp->fp_class = FPC_ZERO;
               else
#endif
                       fp->fp_sticky = 1;
               return (1);
       }

       /* Squish out full words. */
       s = fp->fp_sticky;
       if (rsh >= 32 * 3) {
               s |= m3 | m2 | m1;
               m3 = m0, m2 = 0, m1 = 0, m0 = 0;
       } else if (rsh >= 32 * 2) {
               s |= m3 | m2;
               m3 = m1, m2 = m0, m1 = 0, m0 = 0;
       } else if (rsh >= 32) {
               s |= m3;
               m3 = m2, m2 = m1, m1 = m0, m0 = 0;
       }

       /* Handle any remaining partial word. */
       if ((rsh &= 31) != 0) {
               lsh = 32 - rsh;
               s |= m3 << lsh;
               m3 = (m3 >> rsh) | (m2 << lsh);
               m2 = (m2 >> rsh) | (m1 << lsh);
               m1 = (m1 >> rsh) | (m0 << lsh);
               m0 >>= rsh;
       }
       fp->fp_mant[0] = m0;
       fp->fp_mant[1] = m1;
       fp->fp_mant[2] = m2;
       fp->fp_mant[3] = m3;
       fp->fp_sticky = s;
       return (s);
}

/*
* Force a number to be normal, i.e., make its fraction have all zero
* bits before FP_1, then FP_1, then all 1 bits.  This is used for denorms
* and (sometimes) for intermediate results.
*
* Internally, this may use a `supernormal' -- a number whose fp_mant
* is greater than or equal to 2.0 -- so as a side effect you can hand it
* a supernormal and it will fix it (provided fp->fp_mant[3] == 0).
*/
void
fpu_norm(struct fpn *fp)
{
       u_int m0, m1, m2, m3, top, sup, nrm;
       int lsh, rsh, exp;

       exp = fp->fp_exp;
       m0 = fp->fp_mant[0];
       m1 = fp->fp_mant[1];
       m2 = fp->fp_mant[2];
       m3 = fp->fp_mant[3];

       /* Handle severe subnormals with 32-bit moves. */
       if (m0 == 0) {
               if (m1)
                       m0 = m1, m1 = m2, m2 = m3, m3 = 0, exp -= 32;
               else if (m2)
                       m0 = m2, m1 = m3, m2 = 0, m3 = 0, exp -= 2 * 32;
               else if (m3)
                       m0 = m3, m1 = 0, m2 = 0, m3 = 0, exp -= 3 * 32;
               else {
                       fp->fp_class = FPC_ZERO;
                       return;
               }
       }

       /* Now fix any supernormal or remaining subnormal. */
       nrm = FP_1;
       sup = nrm << 1;
       if (m0 >= sup) {
               /*
                * We have a supernormal number.  We need to shift it right.
                * We may assume m3==0.
                */
               for (rsh = 1, top = m0 >> 1; top >= sup; rsh++) /* XXX slow */
                       top >>= 1;
               exp += rsh;
               lsh = 32 - rsh;
               m3 = m2 << lsh;
               m2 = (m2 >> rsh) | (m1 << lsh);
               m1 = (m1 >> rsh) | (m0 << lsh);
               m0 = top;
       } else if (m0 < nrm) {
               /*
                * We have a regular denorm (a subnormal number), and need
                * to shift it left.
                */
               for (lsh = 1, top = m0 << 1; top < nrm; lsh++)  /* XXX slow */
                       top <<= 1;
               exp -= lsh;
               rsh = 32 - lsh;
               m0 = top | (m1 >> rsh);
               m1 = (m1 << lsh) | (m2 >> rsh);
               m2 = (m2 << lsh) | (m3 >> rsh);
               m3 <<= lsh;
       }

       fp->fp_exp = exp;
       fp->fp_mant[0] = m0;
       fp->fp_mant[1] = m1;
       fp->fp_mant[2] = m2;
       fp->fp_mant[3] = m3;
}

/*
* Concoct a `fresh' Quiet NaN per Appendix N.
* As a side effect, we set NV (invalid) for the current exceptions.
*/
struct fpn *
fpu_newnan(struct fpemu *fe)
{
       struct fpn *fp;

       fp = &fe->fe_f3;
       fp->fp_class = FPC_QNAN;
       fp->fp_sign = 0;
       fp->fp_mant[0] = FP_QUIETBIT;
       fp->fp_mant[1] = fp->fp_mant[2] = fp->fp_mant[3] = 0;
       DUMPFPN(FPE_REG, fp);
       return (fp);
}

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