mach/proto/fp/extend.c

   1 /*
   2   (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
   3   See the copyright notice in the ACK home directory, in the file "Copyright".
   4 */
   5
   6 /* $Id: extend.c,v 1.12 1994/06/24 13:31:57 ceriel Exp $ */
   7
   8 /*
   9         CONVERTS FLOATING POINT TO EXTENDED FORMAT
  10
  11         Two sizes of FLOATING Point are known:
  12                 SINGLE and DOUBLE
  13 */
  14 /********************************************************/
  15 /*
  16         It is not required to normalize in extended
  17         format, but it has been chosen to do so.
  18         Extended Format is as follows (at exit):
  19
  20 ->sign  S000 0000 | 0000 0000           <SIGN>
  21 ->exp   0EEE EEEE | EEEE EEEE           <EXPONENT>
  22 ->m1    LFFF FFFF | FFFF FFFF           <L.Fraction>
  23         FFFF FFFF | FFFF FFFF           <Fraction>
  24 ->m2    FFFF FFFF | FFFF FFFF           <Fraction>
  25         FFFF F000 | 0000 0000           <Fraction>
  26 */
  27 /********************************************************/
  28
  29 #include "FP_bias.h"
  30 #include "FP_shift.h"
  31 #include "FP_types.h"
  32 #include "get_put.h"
  33 /********************************************************/
  34
  35 void
  36 extend(from,to,size)
  37 unsigned long   *from;
  38 EXTEND  *to;
  39 int     size;
  40 {
  41         register char *cpt1;
  42         unsigned long   tmp;
  43         int     leadbit = 0;
  44
  45         cpt1 = (char *) from;
  46
  47 #if FL_MSL_AT_LOW_ADDRESS
  48 #if FL_MSW_AT_LOW_ADDRESS
  49         to->exp = uget2(cpt1);
  50 #else
  51         to->exp = uget2(cpt1+2);
  52 #endif
  53 #else
  54 #if FL_MSW_AT_LOW_ADDRESS
  55         to->exp = uget2(cpt1+(size == sizeof(DOUBLE) ? 4 : 0));
  56 #else
  57         to->exp = uget2(cpt1+(size == sizeof(DOUBLE) ? 6 : 2));
  58 #endif
  59 #endif
  60         to->sign = (to->exp & 0x8000);  /* set sign bit */
  61         to->exp ^= to->sign;
  62         if (size == sizeof(DOUBLE))
  63                 to->exp >>= DBL_EXPSHIFT;
  64         else
  65                 to->exp >>= SGL_EXPSHIFT;
  66         if (to->exp > 0)
  67                 leadbit++;      /* will set Lead bit later      */
  68         else to->exp++;
  69
  70         if (size == sizeof(DOUBLE))     {
  71 #if FL_MSL_AT_LOW_ADDRESS
  72                 to->m1 = get4(cpt1);
  73                 cpt1 += 4;
  74                 tmp = get4(cpt1);
  75 #else
  76                 tmp = get4(cpt1);
  77                 cpt1 += 4;
  78                 to->m1 = get4(cpt1);
  79 #endif
  80                 if (to->exp == 1 && to->m1 == 0 && tmp == 0) {
  81                         to->exp = 0;
  82                         to->sign = 0;
  83                         to->m1 = 0;
  84                         to->m2 = 0;
  85                         return;
  86                 }
  87                 to->m1 <<= DBL_M1LEFT;          /* shift        */
  88                 to->exp -= DBL_BIAS;            /* remove bias  */
  89                 to->m1 |= (tmp>>DBL_RPACK);     /* plus 10 == 32        */
  90                 to->m2 = (tmp<<DBL_LPACK);      /* plus 22 == 32        */
  91         }
  92         else    {       /* size == sizeof(SINGLE)               */
  93                 to->m1 = get4(cpt1);
  94                 to->m1  <<= SGL_M1LEFT; /* shift        */
  95                 if (to->exp == 1 && to->m1 == 0) {
  96                         to->exp = 0;
  97                         to->sign = 0;
  98                         to->m1 = 0;
  99                         to->m2 = 0;
 100                         return;
 101                 }
 102                 to->exp -= SGL_BIAS;            /* remove bias  */
 103                 to->m2 = 0L;
 104         }
 105
 106         to->m1 |= NORMBIT;                              /* set bit L    */
 107         if (leadbit == 0) {             /* set or clear Leading Bit     */
 108                 to->m1 &= ~NORMBIT;                     /* clear bit L  */
 109                 nrm_ext(to);                            /* and normalize */
 110         }
 111 }