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ieee754sp.c

/* IEEE754 floating point arithmetic
 * single precision
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 * http://www.algor.co.uk
 *
 * ########################################################################
 *
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License (Version 2) as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope 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.
 *
 * ########################################################################
 */


#include "ieee754sp.h"

int ieee754sp_class(ieee754sp x)
{
      COMPXSP;
      EXPLODEXSP;
      return xc;
}

int ieee754sp_isnan(ieee754sp x)
{
      return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
}

int ieee754sp_issnan(ieee754sp x)
{
      assert(ieee754sp_isnan(x));
      return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
}


ieee754sp ieee754sp_xcpt(ieee754sp r, const char *op, ...)
{
      struct ieee754xctx ax;

      if (!TSTX())
            return r;

      ax.op = op;
      ax.rt = IEEE754_RT_SP;
      ax.rv.sp = r;
      va_start(ax.ap, op);
      ieee754_xcpt(&ax);
      va_end(ax.ap);
      return ax.rv.sp;
}

ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
{
      struct ieee754xctx ax;

      assert(ieee754sp_isnan(r));

      if (!ieee754sp_issnan(r))     /* QNAN does not cause invalid op !! */
            return r;

      if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
            /* not enabled convert to a quiet NaN */
            SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
            if (ieee754sp_isnan(r))
                  return r;
            else
                  return ieee754sp_indef();
      }

      ax.op = op;
      ax.rt = 0;
      ax.rv.sp = r;
      va_start(ax.ap, op);
      ieee754_xcpt(&ax);
      va_end(ax.ap);
      return ax.rv.sp;
}

ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
{
      assert(ieee754sp_isnan(x));
      assert(ieee754sp_isnan(y));

      if (SPMANT(x) > SPMANT(y))
            return x;
      else
            return y;
}


static unsigned get_rounding(int sn, unsigned xm)
{
      /* inexact must round of 3 bits
       */
      if (xm & (SP_MBIT(3) - 1)) {
            switch (ieee754_csr.rm) {
            case IEEE754_RZ:
                  break;
            case IEEE754_RN:
                  xm += 0x3 + ((xm >> 3) & 1);
                  /* xm += (xm&0x8)?0x4:0x3 */
                  break;
            case IEEE754_RU:  /* toward +Infinity */
                  if (!sn)    /* ?? */
                        xm += 0x8;
                  break;
            case IEEE754_RD:  /* toward -Infinity */
                  if (sn)     /* ?? */
                        xm += 0x8;
                  break;
            }
      }
      return xm;
}


/* generate a normal/denormal number with over,under handling
 * sn is sign
 * xe is an unbiased exponent
 * xm is 3bit extended precision value.
 */
ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
{
      assert(xm);       /* we don't gen exact zeros (probably should) */

      assert((xm >> (SP_MBITS + 1 + 3)) == 0);  /* no execess */
      assert(xm & (SP_HIDDEN_BIT << 3));

      if (xe < SP_EMIN) {
            /* strip lower bits */
            int es = SP_EMIN - xe;

            if (ieee754_csr.nod) {
                  SETCX(IEEE754_UNDERFLOW);
                  SETCX(IEEE754_INEXACT);

                  switch(ieee754_csr.rm) {
                  case IEEE754_RN:
                        return ieee754sp_zero(sn);
                  case IEEE754_RZ:
                        return ieee754sp_zero(sn);
                  case IEEE754_RU:      /* toward +Infinity */
                        if(sn == 0)
                              return ieee754sp_min(0);
                        else
                              return ieee754sp_zero(1);
                  case IEEE754_RD:      /* toward -Infinity */
                        if(sn == 0)
                              return ieee754sp_zero(0);
                        else
                              return ieee754sp_min(1);
                  }
            }

            if (xe == SP_EMIN - 1
                        && get_rounding(sn, xm) >> (SP_MBITS + 1 + 3))
            {
                  /* Not tiny after rounding */
                  SETCX(IEEE754_INEXACT);
                  xm = get_rounding(sn, xm);
                  xm >>= 1;
                  /* Clear grs bits */
                  xm &= ~(SP_MBIT(3) - 1);
                  xe++;
            }
            else {
                  /* sticky right shift es bits
                   */
                  SPXSRSXn(es);
                  assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
                  assert(xe == SP_EMIN);
            }
      }
      if (xm & (SP_MBIT(3) - 1)) {
            SETCX(IEEE754_INEXACT);
            if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
                  SETCX(IEEE754_UNDERFLOW);
            }

            /* inexact must round of 3 bits
             */
            xm = get_rounding(sn, xm);
            /* adjust exponent for rounding add overflowing
             */
            if (xm >> (SP_MBITS + 1 + 3)) {
                  /* add causes mantissa overflow */
                  xm >>= 1;
                  xe++;
            }
      }
      /* strip grs bits */
      xm >>= 3;

      assert((xm >> (SP_MBITS + 1)) == 0);      /* no execess */
      assert(xe >= SP_EMIN);

      if (xe > SP_EMAX) {
            SETCX(IEEE754_OVERFLOW);
            SETCX(IEEE754_INEXACT);
            /* -O can be table indexed by (rm,sn) */
            switch (ieee754_csr.rm) {
            case IEEE754_RN:
                  return ieee754sp_inf(sn);
            case IEEE754_RZ:
                  return ieee754sp_max(sn);
            case IEEE754_RU:  /* toward +Infinity */
                  if (sn == 0)
                        return ieee754sp_inf(0);
                  else
                        return ieee754sp_max(1);
            case IEEE754_RD:  /* toward -Infinity */
                  if (sn == 0)
                        return ieee754sp_max(0);
                  else
                        return ieee754sp_inf(1);
            }
      }
      /* gen norm/denorm/zero */

      if ((xm & SP_HIDDEN_BIT) == 0) {
            /* we underflow (tiny/zero) */
            assert(xe == SP_EMIN);
            if (ieee754_csr.mx & IEEE754_UNDERFLOW)
                  SETCX(IEEE754_UNDERFLOW);
            return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
      } else {
            assert((xm >> (SP_MBITS + 1)) == 0);      /* no execess */
            assert(xm & SP_HIDDEN_BIT);

            return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
      }
}

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