FloatingPointUnit < MecrispCube

---+ Floating Point Unit

   * https://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Number-Conversion.html#Number-Conversion
   * https://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Floating-Point.html#Floating-Point
   * https://forth-standard.org/standard/float
   * https://forth-standard.org/proposals/recognizer#contribution-142
   * https://de.wikipedia.org/wiki/IEEE_754
   * https://interrupt.memfault.com/blog/cortex-m-rtos-context-switching ARM Cortex-M RTOS Context Switching
   * printf("%f", myFloat) f. fe. fs.
   * atof() oder strtof() benutzen? 
   * nur single-precision? (7..8 Dezimalstellen, H7 hat double precision FPU)
   * kein eigener Stack
   * >float wo?
   * float register mit mutex absichern?
   * float.fs in source integrieren?
   * auf float in ISR verzichten
   * _FPU_USED
   * AN4044 Application note, Foating point unit demonstration on STM32 microcontrollers 
   * math.h e.g.  float cosf (float)

=>float= in Gforth engine/support.c verwendet =strtod()= (=strtof()= for single precision)
<verbatim>
Cell to_float(Char *c_addr, UCell u, Float *rp)
{
  /* convertible string := <significand>[<exponent>]
     <significand> := [<sign>]{<digits>[.<digits0>] | .<digits> }
     <exponent>    := <marker><digits0>
     <marker>      := {<e-form> | <sign-form>}
     <e-form>      := <e-char>[<sign-form>]
     <sign-form>   := { + | - }
     <e-char>      := { D | d | E | e }
  */
  Char *s = c_addr;
  Char c;
  Char *send = c_addr+u;
  UCell ndigits = 0;
  UCell ndots = 0;
  UCell edigits = 0;
  char cnum[u+3]; /* append at most "e0\0" */
  char *t=cnum;
  char *endconv;
  Float r;
  
  if (s >= send) /* treat empty string as 0e */
    goto return0;
  switch ((c=*s)) {
  case ' ':
    /* "A string of blanks should be treated as a special case
       representing zero."*/
    for (s++; s<send; )
      if (*s++ != ' ')
        goto error;
    goto return0;
  case '-':
  case '+': *t++ = c; s++; goto aftersign;
  }
  aftersign: 
  if (s >= send)
    goto exponent;
  switch (c=*s) {
  case '0' ... '9': *t++ = c; ndigits++; s++; goto aftersign;
  case '.':         *t++ = c; ndots++;   s++; goto aftersign;
  default:                                    goto exponent;
  }
 exponent:
  if (ndigits < 1 || ndots > 1)
    goto error;
  *t++ = 'E';
  if (s >= send)
    goto done;
  switch (c=*s) {
  case 'D':
  case 'd':
  case 'E':
  case 'e': s++; break;
  }
  if (s >= send)
    goto done;
  switch (c=*s) {
  case '+':
  case '-': *t++ = c; s++; break;
  }
 edigits0:
  if (s >= send)
    goto done;
  switch (c=*s) {
  case '0' ... '9': *t++ = c; s++; edigits++; goto edigits0;
  default: goto error;
  }
 done:
  if (edigits == 0)
    *t++ = '0';
  *t++ = '\0';
  assert(t-cnum <= u+3);
  r = strtod(cnum, &endconv);
  assert(*endconv == '\0');
  *rp = r;
  return -1;
 return0:
  *rp = 0.0;
  return -1;
 error:
  *rp = 0.0;
  return 0;
}
#endif
</verbatim>


-- %USERSIG{PeterSchmid - 2020-10-27}%

---++ Comments

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This topic: MecrispCube > WebHome > FloatingPointUnit
Topic revision: r8 - 2022-10-27 - PeterSchmid