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sfrem.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/sfrem.c       $Revision: 1.1 $
 *
 *  Purpose:
 *    Single Precision Floating-point Remainder
 *
 *  External Interfaces:
 *    sgl_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 "sgl_float.h"

/*
 *  Single Precision Floating-point Remainder
 */

int
sgl_frem (sgl_floating_point * srcptr1, sgl_floating_point * srcptr2,
        sgl_floating_point * dstptr, unsigned int *status)
{
      register unsigned int opnd1, opnd2, result;
      register int opnd1_exponent, opnd2_exponent, dest_exponent, stepcount;
      register boolean roundup = FALSE;

      opnd1 = *srcptr1;
      opnd2 = *srcptr2;
      /*
       * check first operand for NaN's or infinity
       */
      if ((opnd1_exponent = Sgl_exponent(opnd1)) == SGL_INFINITY_EXPONENT) {
            if (Sgl_iszero_mantissa(opnd1)) {
                  if (Sgl_isnotnan(opnd2)) {
                        /* invalid since first operand is infinity */
                        if (Is_invalidtrap_enabled()) 
                                    return(INVALIDEXCEPTION);
                                Set_invalidflag();
                                Sgl_makequietnan(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 ((opnd2_exponent = Sgl_exponent(opnd2)) == SGL_INFINITY_EXPONENT) {
            if (Sgl_iszero_mantissa(opnd2)) {
                  /*
                   * return first operand
                   */
                  *dstptr = opnd1;
                  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);
      }
      /*
       * check second operand for zero
       */
      if (Sgl_iszero_exponentmantissa(opnd2)) {
            /* invalid since second operand is zero */
            if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                Set_invalidflag();
                Sgl_makequietnan(result);
            *dstptr = result;
            return(NOEXCEPTION);
      }

      /* 
       * get sign of result
       */
      result = opnd1;  

      /* 
       * check for denormalized operands
       */
      if (opnd1_exponent == 0) {
            /* check for zero */
            if (Sgl_iszero_mantissa(opnd1)) {
                  *dstptr = opnd1;
                  return(NOEXCEPTION);
            }
            /* normalize, then continue */
            opnd1_exponent = 1;
            Sgl_normalize(opnd1,opnd1_exponent);
      }
      else {
            Sgl_clear_signexponent_set_hidden(opnd1);
      }
      if (opnd2_exponent == 0) {
            /* normalize, then continue */
            opnd2_exponent = 1;
            Sgl_normalize(opnd2,opnd2_exponent);
      }
      else {
            Sgl_clear_signexponent_set_hidden(opnd2);
      }

      /* 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 && Sgl_isgreaterthan(opnd1,opnd2)) {
                  Sgl_all(result) = ~Sgl_all(result);   /* set sign */
                  /* align opnd2 with opnd1 */
                  Sgl_leftshiftby1(opnd2); 
                  Sgl_subtract(opnd2,opnd1,opnd2);
                  /* now normalize */
                  while (Sgl_iszero_hidden(opnd2)) {
                              Sgl_leftshiftby1(opnd2);
                              dest_exponent--;
                  }
                  Sgl_set_exponentmantissa(result,opnd2);
                  goto testforunderflow;
            }
            /*
             * opnd1/opnd2 <= 1/2
             *
             * In this case n will round to zero, so 
             *    r = opnd1
             */
            Sgl_set_exponentmantissa(result,opnd1);
            dest_exponent = opnd1_exponent;
            goto testforunderflow;
      }

      /*
       * Generate result
       *
       * Do iterative subtract until remainder is less than operand 2.
       */
      while (stepcount-- > 0 && Sgl_all(opnd1)) {
            if (Sgl_isnotlessthan(opnd1,opnd2))
                  Sgl_subtract(opnd1,opnd2,opnd1);
            Sgl_leftshiftby1(opnd1);
      }
      /*
       * Do last subtract, then determine which way to round if remainder 
       * is exactly 1/2 of opnd2 
       */
      if (Sgl_isnotlessthan(opnd1,opnd2)) {
            Sgl_subtract(opnd1,opnd2,opnd1);
            roundup = TRUE;
      }
      if (stepcount > 0 || Sgl_iszero(opnd1)) {
            /* division is exact, remainder is zero */
            Sgl_setzero_exponentmantissa(result);
            *dstptr = result;
            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.
       */
      Sgl_leftshiftby1(opnd1);
      if (Sgl_isgreaterthan(opnd1,opnd2)) {
            Sgl_invert_sign(result);
            Sgl_subtract((opnd2<<1),opnd1,opnd1);
      }
      /* check for remainder being exactly 1/2 of opnd2 */
      else if (Sgl_isequal(opnd1,opnd2) && roundup) { 
            Sgl_invert_sign(result);
      }

      /* normalize result's mantissa */
        while (Sgl_iszero_hidden(opnd1)) {
                dest_exponent--;
                Sgl_leftshiftby1(opnd1);
        }
      Sgl_set_exponentmantissa(result,opnd1);

        /* 
         * Test for underflow
         */
    testforunderflow:
      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;
                  /* frem is always exact */
                  return(UNDERFLOWEXCEPTION);
                }
                /*
                 * denormalize result or set to signed zero
                 */
                if (dest_exponent >= (1 - SGL_P)) {
                  Sgl_rightshift_exponentmantissa(result,1-dest_exponent);
                }
                else {
                  Sgl_setzero_exponentmantissa(result);
            }
      }
      else Sgl_set_exponent(result,dest_exponent);
      *dstptr = result;
      return(NOEXCEPTION);
}

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