#include <sys/types.h>
#include <i86.h>
#include <dos.h>

#include "dpmi.h"

static uint16_t vbeDOSBufferDPMISelector = 0;

/**
* This is memory accessible to real-mode x86, so that
* interrupts can access the data.
*/
void *dpmiAllocateDOSMemory(int size) {
  union REGS regs;

  // a paragraph is 16 bytes because why not
  unsigned short sizeParagraphs = (size + 15) >> 4UL;

  regs.w.ax = 0x0100;
  regs.w.bx = sizeParagraphs;
  int386(0x31, &regs, &regs);

  vbeDOSBufferDPMISelector = regs.w.dx;
  return (void *)(((unsigned long)regs.w.ax) << 4UL);
}

void dpmiDeallocateDOSMemory() {
  union REGS regs;

  regs.w.ax = 0x0101;
  regs.w.dx = vbeDOSBufferDPMISelector;
  int386(0x31, &regs, &regs);
}

/**
 * You only need to use this if you're passing a DPMI-allocated
 * memory struture to an interrupt via ES:DI. Otherwise, a
 * regular int386 call is sufficient.
 */
void dpmiInt(int interruptNo, struct dpmiRealModeRegs *rc) {
  union REGS regs;

  // call the DPMI real mode interrupt handler
  regs.w.ax = 0x0300;
  regs.w.bx = interruptNo; // real mode interrupt
  regs.w.cx = 0;           // don't mess with our stack
  regs.x.edi = (unsigned int)rc;

  int386(0x31, &regs, &regs);
}