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From: "Ozkan Sezer (sezeroz AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Date: Sat, 24 Feb 2024 00:11:46 +0300
Message-ID: <CAA2C=vB8ZicddhV9vbcu9RELueGs8o5_=OQdy0gejtPzFaYeJw@mail.gmail.com>
Subject: checking int2d amis appstring with djgpp
To: djgpp <djgpp AT delorie DOT com>
Content-Type: text/plain; charset="UTF-8"
Reply-To: djgpp AT delorie DOT com

Hi everyone:

Does the following DJGPP port of SBEMU detection look correct?
It is an adaptation from a WatcomC (32 bit flat) code in here:
https://github.com/wbcbz7/sndlib-watcom/blob/master/sndlib.cpp#L41-L71

(I'm fairly rusty in gcc inline asm and djgpp address mapping, etc,
thanks in advance.)

 int sndlib_sbemu_detect(void)
{
  __dpmi_raddr addr;
  uint32_t r_addr;
  char* appstring;
  int mx;

  /* check for INT2D vector == NULL */
  __dpmi_get_real_mode_interrupt_vector(0x2D, &addr);
  r_addr = ((uint32_t)addr.segment<<4) + (uint32_t)addr.offset16;
  if (!r_addr) return -1;

  /* scan all multiplexes of INT 2D */
  for (mx = 0; mx < 256; mx++)
  {
    __asm__ __volatile__ ("movb %0,%%ah"::"m"(mx));
    __asm__ __volatile__ (
      "xorb %al, %al\n"
      "int  $0x2d\n"
      "cmpb $0xFF, %al\n" /* is this a free multiplex? */
      "jz  _found\n"
      "xorw %dx, %dx\n" /* it is, return NULL pointer */
      "xorw %di, %di\n"
     "_found:\n");
    __asm__ __volatile__ ("movw %%dx,%0":"=m"(addr.segment));
    __asm__ __volatile__ ("movw %%di,%0":"=m"(addr.offset16));

    /* check for SBEMU application string */
    r_addr = ((uint32_t)addr.segment<<4) + (uint32_t)addr.offset16;
    if (!r_addr) continue;
    appstring = (char *)real2ptr(r_addr);
    if (memcmp(appstring + 8,"SBEMU",5) == 0)
      return mx;
  }

  return -1;
}


P.S.: real2ptr() in there actually returns
    (void *) (real += __djgpp_conventional_base)
after a successful __djgpp_nearptr_enable()

--
O.S.