Subversion Repositories pentevo

Rev

Blame | Last modification | View Log | Download | RSS feed

  1. /* milfloat.h */
  2. /*****************************************************************************/
  3. /* SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only                     */
  4. /*                                                                           */
  5. /* AS                                                                        */
  6. /*                                                                           */
  7. /* IEEE -> MIL STD 1750 Floating Point Conversion on host                    */
  8. /*                                                                           */
  9. /*****************************************************************************/
  10.  
  11. #include <stdio.h>
  12. #include <errno.h>
  13. #include "as_float.h"
  14. #include "milfloat.h"
  15.  
  16. /*!------------------------------------------------------------------------
  17.  * \fn     as_float_2_mil1750(as_float_t inp, Word *p_dest, Boolean extended)
  18.  * \brief  convert host float to MIL STD 1750
  19.  * \param  inp number to convert
  20.  * \param  p_dest destination buffer
  21.  * \param  extended convert to 32 or 48 bit format?
  22.  * \return # of words written or < 0 if error
  23.  * ------------------------------------------------------------------------ */
  24.  
  25. int as_float_2_mil1750(as_float_t inp, Word *p_dest, Boolean extended)
  26. {
  27.   as_float_dissect_t dissect;
  28.   Word or_sum;
  29.   unsigned req_mantissa_bits;
  30.  
  31.   /* Dissect number: */
  32.  
  33.   as_float_dissect(&dissect, inp);
  34.  
  35.   /* NaN and Infinity cannot be represented: */
  36.  
  37.   if ((dissect.fp_class == AS_FP_NAN)
  38.    || (dissect.fp_class == AS_FP_INFINITE))
  39.     return -EINVAL;
  40.  
  41.   /* Mantissa is in range [-1,+1) instead of [-2,+2): */
  42.  
  43.   dissect.exponent++;
  44.  
  45.   /* If exponent is too small to represent, shift down mantissa
  46.      until exponent is large enough, or mantissa is all-zeroes: */
  47.  
  48.   while ((dissect.exponent < -128) && !as_float_mantissa_is_zero(&dissect))
  49.   {
  50.     as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits);
  51.     dissect.exponent++;
  52.   }
  53.  
  54.   /* exponent overflow? */
  55.  
  56.   if (dissect.exponent > 127)
  57.     return -E2BIG;
  58.  
  59.   /* Form 2s complement of mantissa when sign is set: */
  60.  
  61.   as_float_mantissa_twos_complement(&dissect);
  62.  
  63.   /* Normalize, so that topmost bits of mantissa are unequal.  This happens
  64.      for powers of two, after negating: */
  65.  
  66.   switch (as_float_mantissa_extract(&dissect, 0, 2))
  67.   {
  68.     case 0:
  69.     case 3:
  70.       if (dissect.exponent > -127) /* -128? */
  71.       {
  72.         dissect.exponent--;
  73.         as_float_mantissa_shift_left(dissect.mantissa, 0, dissect.mantissa_bits);
  74.       }
  75.       break;
  76.   }
  77.  
  78.   /* no rounding: */
  79.  
  80.   req_mantissa_bits = extended ? 40 : 24;
  81.   if (req_mantissa_bits > dissect.mantissa_bits)
  82.     as_float_append_mantissa_bits(&dissect, 0, req_mantissa_bits - dissect.mantissa_bits);
  83.  
  84.   /* Write out result: */
  85.  
  86.   or_sum  = (p_dest[0] = as_float_mantissa_extract(&dissect, 0, 16));
  87.   or_sum |= (p_dest[1] = as_float_mantissa_extract(&dissect, 16, 8) << 8);
  88.   if (extended)
  89.     or_sum |= (p_dest[2] = as_float_mantissa_extract(&dissect, 24, 16));
  90.  
  91.   /* zero mantissa means zero exponent */
  92.  
  93.   if (or_sum)
  94.     p_dest[1] |= dissect.exponent & 0xff;
  95.  
  96.   return extended ? 3 : 2;
  97. }
  98.