/*
   This program just hooks INT 16h and increments a byte on the screen every
   time INT 16h is called in real mode. It executes COMMAND.COM, when you exit
   that, the program terminates.
*/

/*北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北
  INTERFACE
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#include "pmc.h"

// Minimize memory used.

int   _extheapmax       = 0;
int   _lowbuflen        = 1024;
int   _PMrmstacks       = 1;
int   _PMpmstacks       = 1;
int   _pmcrmstacklen    = 0;
int   _rmcpmstacklen    = 0;
int   _pmcrmstacks      = 0;
int   _rmcpmstacks      = 0;

REGSTRUCT *__pascal cint16 (REGSTRUCT *r);

/*北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北
  DATA
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REGSTRUCT rs2;
SEGOFF ormiv, cb;

/*北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北北
  CODE
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//屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯屯
void __cdecl PMmain (void)
{
  PTR p0, p1;

// Set up DPMI callback C function.
  p0 = setcb (&cb, NULL, &rs2, cint16);

// Get old INT 16h address and set new to callback just allocated.
  iv_rmget (0x16, &ormiv);
  iv_rmset (0x16, cb.off, cb.seg);

// Execute command shell (COMMAND.COM). Can't use the value from the getenv
// function directly because it is int the low memory buffer area which is
// used by the fileexec function.
  fileexec (p1 = strdup (getenv ("COMSPEC")), NULL);

// Reset old INT 16h handler.
  iv_rmset (0x16, ormiv.off, ormiv.seg);

// Free DPMI callback and duplicated string.
  free (p1);
  resetcb (SEGOFFtoDWORD (cb), p0);
}

/*鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍
  INT 16h protected mode handler.
  In:
    REGSTRUCT *r = register structure containing real mode register values
  Out:
    REGSTRUCT * = register structure containing real mode register values
鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍鞍*/
REGSTRUCT *__pascal cint16 (REGSTRUCT *r)
{
  (*(BYTE *)rlp (0xb8000)) ++;

// Set real mode resume address to old real mode INT 16h handler.
  r->d.CSIP = SEGOFFtoDWORD (ormiv);

  return r;
}