source: trunk/minix/lib/ack/fphook/extend.fc@ 12

/*
  (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
  See the copyright notice in the ACK home directory, in the file "Copyright".
*/

/* $Header: /cvsup/minix/src/lib/ack/fphook/extend.fc,v 1.1 2005/10/10 15:27:43 beng Exp $ */

/*
        CONVERTS FLOATING POINT TO EXTENDED FORMAT

        Two sizes of FLOATING Point are known:
                SINGLE and DOUBLE
*/
/********************************************************/
/*
        It is not required to normalize in extended
        format, but it has been chosen to do so.
        Extended Format is as follows (at exit):

->sign  S000 0000 | 0000 0000           <SIGN>
->exp   0EEE EEEE | EEEE EEEE           <EXPONENT>
->m1    LFFF FFFF | FFFF FFFF           <L.Fraction>
        FFFF FFFF | FFFF FFFF           <Fraction>
->m2    FFFF FFFF | FFFF FFFF           <Fraction>
        FFFF F000 | 0000 0000           <Fraction>
*/
/********************************************************/

#include "FP_bias.h"
#include "FP_shift.h"
#include "FP_types.h"
#include "get_put.h"
/********************************************************/

void
extend(from,to,size)
unsigned long   *from;
EXTEND  *to;
int     size;
{
        register char *cpt1;
        unsigned long   tmp;
        int     leadbit = 0;

        cpt1 = (char *) from;

#if FL_MSL_AT_LOW_ADDRESS
#if FL_MSW_AT_LOW_ADDRESS
        to->exp = uget2(cpt1);
#else
        to->exp = uget2(cpt1+2);
#endif
#else
#if FL_MSW_AT_LOW_ADDRESS
        to->exp = uget2(cpt1+(size == sizeof(DOUBLE) ? 4 : 0));
#else
        to->exp = uget2(cpt1+(size == sizeof(DOUBLE) ? 6 : 2));
#endif
#endif
        to->sign = (to->exp & 0x8000);  /* set sign bit */
        to->exp ^= to->sign;
        if (size == sizeof(DOUBLE))
                to->exp >>= DBL_EXPSHIFT;
        else
                to->exp >>= SGL_EXPSHIFT;
        if (to->exp > 0)
                leadbit++;      /* will set Lead bit later      */
        else to->exp++;

        if (size == sizeof(DOUBLE))     {
#if FL_MSL_AT_LOW_ADDRESS
                to->m1 = get4(cpt1);
                cpt1 += 4;
                tmp = get4(cpt1);
#else
                tmp = get4(cpt1);
                cpt1 += 4;
                to->m1 = get4(cpt1);
#endif
                if (to->exp == 1 && to->m1 == 0 && tmp == 0) {
                        to->exp = 0;
                        to->sign = 0;
                        to->m1 = 0;
                        to->m2 = 0;
                        return;
                }
                to->m1 <<= DBL_M1LEFT;          /* shift        */
                to->exp -= DBL_BIAS;            /* remove bias  */
                to->m1 |= (tmp>>DBL_RPACK);     /* plus 10 == 32        */
                to->m2 = (tmp<<DBL_LPACK);      /* plus 22 == 32        */
        }
        else    {       /* size == sizeof(SINGLE)               */
                to->m1 = get4(cpt1);
                to->m1  <<= SGL_M1LEFT; /* shift        */
                if (to->exp == 1 && to->m1 == 0) {
                        to->exp = 0;
                        to->sign = 0;
                        to->m1 = 0;
                        to->m2 = 0;
                        return;
                }
                to->exp -= SGL_BIAS;            /* remove bias  */
                to->m2 = 0L;
        }

        to->m1 |= NORMBIT;                              /* set bit L    */
        if (leadbit == 0) {             /* set or clear Leading Bit     */
                to->m1 &= ~NORMBIT;                     /* clear bit L  */
                nrm_ext(to);                            /* and normalize */
        }
}