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sfmpy.c

/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
 *
 *    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/sfmpy.c       $Revision: 1.1 $
 *
 *  Purpose:
 *    Single Precision Floating-point Multiply
 *
 *  External Interfaces:
 *    sgl_fmpy(srcptr1,srcptr2,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"

/*
 *  Single Precision Floating-point Multiply
 */

int
sgl_fmpy(
    sgl_floating_point *srcptr1,
    sgl_floating_point *srcptr2,
    sgl_floating_point *dstptr,
    unsigned int *status)
{
      register unsigned int opnd1, opnd2, opnd3, result;
      register int dest_exponent, count;
      register boolean inexact = FALSE, guardbit = FALSE, stickybit = FALSE;
      boolean is_tiny;

      opnd1 = *srcptr1;
      opnd2 = *srcptr2;
      /* 
       * set sign bit of result 
       */
      if (Sgl_sign(opnd1) ^ Sgl_sign(opnd2)) Sgl_setnegativezero(result);  
      else Sgl_setzero(result);
      /*
       * check first operand for NaN's or infinity
       */
      if (Sgl_isinfinity_exponent(opnd1)) {
            if (Sgl_iszero_mantissa(opnd1)) {
                  if (Sgl_isnotnan(opnd2)) {
                        if (Sgl_iszero_exponentmantissa(opnd2)) {
                              /* 
                               * invalid since operands are infinity 
                               * and zero 
                               */
                              if (Is_invalidtrap_enabled()) 
                                          return(INVALIDEXCEPTION);
                                    Set_invalidflag();
                                    Sgl_makequietnan(result);
                              *dstptr = result;
                              return(NOEXCEPTION);
                        }
                        /*
                         * return infinity
                         */
                        Sgl_setinfinity_exponentmantissa(result);
                        *dstptr = result;
                        return(NOEXCEPTION);
                  }
            }
            else {
                  /*
                   * is NaN; signaling or quiet?
                   */
                  if (Sgl_isone_signaling(opnd1)) {
                              /* trap if INVALIDTRAP enabled */
                              if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                              /* make NaN quiet */
                              Set_invalidflag();
                              Sgl_set_quiet(opnd1);
                  }
                  /* 
                   * is second operand a signaling NaN? 
                   */
                  else if (Sgl_is_signalingnan(opnd2)) {
                              /* trap if INVALIDTRAP enabled */
                              if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                              /* make NaN quiet */
                              Set_invalidflag();
                              Sgl_set_quiet(opnd2);
                        *dstptr = opnd2;
                        return(NOEXCEPTION);
                  }
                  /*
                   * return quiet NaN
                   */
                  *dstptr = opnd1;
                  return(NOEXCEPTION);
            }
      }
      /*
       * check second operand for NaN's or infinity
       */
      if (Sgl_isinfinity_exponent(opnd2)) {
            if (Sgl_iszero_mantissa(opnd2)) {
                  if (Sgl_iszero_exponentmantissa(opnd1)) {
                        /* invalid since operands are zero & infinity */
                        if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                                Set_invalidflag();
                                Sgl_makequietnan(opnd2);
                        *dstptr = opnd2;
                        return(NOEXCEPTION);
                  }
                  /*
                   * return infinity
                   */
                  Sgl_setinfinity_exponentmantissa(result);
                  *dstptr = result;
                  return(NOEXCEPTION);
            }
                /*
                 * is NaN; signaling or quiet?
                 */
                if (Sgl_isone_signaling(opnd2)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);

                        /* make NaN quiet */
                        Set_invalidflag();
                        Sgl_set_quiet(opnd2);
                }
                /*
                 * return quiet NaN
                 */
                *dstptr = opnd2;
                return(NOEXCEPTION);
      }
      /*
       * Generate exponent 
       */
      dest_exponent = Sgl_exponent(opnd1) + Sgl_exponent(opnd2) - SGL_BIAS;

      /*
       * Generate mantissa
       */
      if (Sgl_isnotzero_exponent(opnd1)) {
            /* set hidden bit */
            Sgl_clear_signexponent_set_hidden(opnd1);
      }
      else {
            /* check for zero */
            if (Sgl_iszero_mantissa(opnd1)) {
                  Sgl_setzero_exponentmantissa(result);
                  *dstptr = result;
                  return(NOEXCEPTION);
            }
                /* is denormalized, adjust exponent */
                Sgl_clear_signexponent(opnd1);
            Sgl_leftshiftby1(opnd1);
            Sgl_normalize(opnd1,dest_exponent);
      }
      /* opnd2 needs to have hidden bit set with msb in hidden bit */
      if (Sgl_isnotzero_exponent(opnd2)) {
            Sgl_clear_signexponent_set_hidden(opnd2);
      }
      else {
            /* check for zero */
            if (Sgl_iszero_mantissa(opnd2)) {
                  Sgl_setzero_exponentmantissa(result);
                  *dstptr = result;
                  return(NOEXCEPTION);
            }
                /* is denormalized; want to normalize */
                Sgl_clear_signexponent(opnd2);
                Sgl_leftshiftby1(opnd2);
            Sgl_normalize(opnd2,dest_exponent);
      }

      /* Multiply two source mantissas together */

      Sgl_leftshiftby4(opnd2);     /* make room for guard bits */
      Sgl_setzero(opnd3);
      /*
       * Four bits at a time are inspected in each loop, and a
       * simple shift and add multiply algorithm is used.
       */
      for (count=1;count<SGL_P;count+=4) {
            stickybit |= Slow4(opnd3);
            Sgl_rightshiftby4(opnd3);
            if (Sbit28(opnd1)) Sall(opnd3) += (Sall(opnd2) << 3);
            if (Sbit29(opnd1)) Sall(opnd3) += (Sall(opnd2) << 2);
            if (Sbit30(opnd1)) Sall(opnd3) += (Sall(opnd2) << 1);
            if (Sbit31(opnd1)) Sall(opnd3) += Sall(opnd2);
            Sgl_rightshiftby4(opnd1);
      }
      /* make sure result is left-justified */
      if (Sgl_iszero_sign(opnd3)) {
            Sgl_leftshiftby1(opnd3);
      }
      else {
            /* result mantissa >= 2. */
            dest_exponent++;
      }
      /* check for denormalized result */
      while (Sgl_iszero_sign(opnd3)) {
            Sgl_leftshiftby1(opnd3);
            dest_exponent--;
      }
      /*
       * check for guard, sticky and inexact bits
       */
      stickybit |= Sgl_all(opnd3) << (SGL_BITLENGTH - SGL_EXP_LENGTH + 1);
      guardbit = Sbit24(opnd3);
      inexact = guardbit | stickybit;

      /* re-align mantissa */
      Sgl_rightshiftby8(opnd3);

      /* 
       * round result 
       */
      if (inexact && (dest_exponent>0 || Is_underflowtrap_enabled())) {
            Sgl_clear_signexponent(opnd3);
            switch (Rounding_mode()) {
                  case ROUNDPLUS: 
                        if (Sgl_iszero_sign(result)) 
                              Sgl_increment(opnd3);
                        break;
                  case ROUNDMINUS: 
                        if (Sgl_isone_sign(result)) 
                              Sgl_increment(opnd3);
                        break;
                  case ROUNDNEAREST:
                        if (guardbit) {
                        if (stickybit || Sgl_isone_lowmantissa(opnd3))
                              Sgl_increment(opnd3);
                        }
            }
            if (Sgl_isone_hidden(opnd3)) dest_exponent++;
      }
      Sgl_set_mantissa(result,opnd3);

        /* 
         * Test for overflow
         */
      if (dest_exponent >= SGL_INFINITY_EXPONENT) {
                /* trap if OVERFLOWTRAP enabled */
                if (Is_overflowtrap_enabled()) {
                        /*
                         * 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);
                }
            inexact = TRUE;
            Set_overflowflag();
                /* 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()) {
                        /*
                         * 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);
                }

            /* Determine if should set underflow flag */
            is_tiny = TRUE;
            if (dest_exponent == 0 && inexact) {
                  switch (Rounding_mode()) {
                  case ROUNDPLUS: 
                        if (Sgl_iszero_sign(result)) {
                              Sgl_increment(opnd3);
                              if (Sgl_isone_hiddenoverflow(opnd3))
                                  is_tiny = FALSE;
                              Sgl_decrement(opnd3);
                        }
                        break;
                  case ROUNDMINUS: 
                        if (Sgl_isone_sign(result)) {
                              Sgl_increment(opnd3);
                              if (Sgl_isone_hiddenoverflow(opnd3))
                                  is_tiny = FALSE;
                              Sgl_decrement(opnd3);
                        }
                        break;
                  case ROUNDNEAREST:
                        if (guardbit && (stickybit || 
                            Sgl_isone_lowmantissa(opnd3))) {
                                    Sgl_increment(opnd3);
                              if (Sgl_isone_hiddenoverflow(opnd3))
                                  is_tiny = FALSE;
                              Sgl_decrement(opnd3);
                        }
                        break;
                  }
            }

                /*
                 * denormalize result or set to signed zero
                 */
            stickybit = inexact;
            Sgl_denormalize(opnd3,dest_exponent,guardbit,stickybit,inexact);

            /* return zero or smallest number */
            if (inexact) {
                  switch (Rounding_mode()) {
                  case ROUNDPLUS: 
                        if (Sgl_iszero_sign(result)) {
                              Sgl_increment(opnd3);
                        }
                        break;
                  case ROUNDMINUS: 
                        if (Sgl_isone_sign(result)) {
                              Sgl_increment(opnd3);
                        }
                        break;
                  case ROUNDNEAREST:
                        if (guardbit && (stickybit || 
                            Sgl_isone_lowmantissa(opnd3))) {
                                    Sgl_increment(opnd3);
                        }
                        break;
                  }
                if (is_tiny) Set_underflowflag();
            }
            Sgl_set_exponentmantissa(result,opnd3);
      }
      else Sgl_set_exponent(result,dest_exponent);
      *dstptr = result;

      /* check for inexact */
      if (inexact) {
            if (Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
            else Set_inexactflag();
      }
      return(NOEXCEPTION);
}

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