nancygold's Journal

Kinda getting used to DOS programming
But it is really quirky. For example, here is the code to print he amount of memory available to program:

#include <dos.h>

int main(int argc, char **argv) {
  char buf[80];
  dos_psp_t _seg *pPSP = (void _seg*)_psp;
  int32_t avail = ((int32_t)(pPSP->himem - _psp) + 1) << 4;
  printf("Memory available: %s\n", litoa10(buf, avail));
  return 0;
}

The _seg is a special keyword to convert uint16_t segment value into a pointer.
litoa10 is basically a itoa(x,10), but for 32bit ints, since the library one works only with 16bit ones.
32bit integers are implemented in software, so the decompiled code is littered with calls like LXLSH@

The litoa10 code is just something....

char *litoa10(char *buf, int32_t n) {
  bool sign;
  size_t len;
  char digit;
  
  if ((0xffff < n) || ((-1 < n && (true)))) {
    sign = false;
  } else {
    sign = true;
    n = CONCAT22(-(n != 0)-_22(n),-n);
  }
  digit = n%10;
  *buf = digit + '0';
  buf[1] = 0;
  while( true ) {
    digit = n/10;
    if (digit == 0) break;
    len = strlen(buf);
    if ((len & 3) == 3) {
      len = strlen(buf);
      memmove(buf + 1,buf,len + 1);
      *buf = ',';
    }
    len = strlen(buf);
    memmove(buf + 1,buf,len + 1);
    n = n/10;
    digit = n%10;
    *buf = digit + '0';
  }
  if (sign) {
    len = strlen(buf);
    memmove(buf + 1,buf,len + 1);
    *buf = '-';
  }
  return buf;
}

first time I see memmove in an integer printing routine.

Current Mood: amused