#include "doscall.hpp"
#include <stdlib.h>
#include <i86.h>
#include <string.hpp>


void RM_intr(int intr, struct rminfo *rm)      // do a real-mode interrupt
{
  union REGS regs;
  struct SREGS sregs;
  memset(&sregs,0,sizeof(sregs));
  regs.w.ax=0x0300;
  regs.w.bx=intr;
  regs.w.cx=0;
  sregs.es=FP_SEG(rm);
  regs.x.edi=FP_OFF(rm);
  int386x(0x31,&regs,&regs,&sregs);  
} ;

void *alloc_low_memory(long size)            // size in bytes
{
  rminfo rm;
  memset(&rm,0,sizeof(rm));
  rm.eax=0x4800;
  rm.ebx=(size+15)/16;
  RM_intr(0x21,&rm);
  if (rm.flags&1)
    return NULL;
  else return (void *)((rm.eax&0xffff)<<4);
}

void free_low_memory(void *ptr)
{
  rminfo rm;
  memset(&rm,0,sizeof(rm));
  rm.eax=0x4900;
  rm.es=((unsigned long)ptr)>>4;
  RM_intr(0x21,&rm);
  if (rm.flags&1)
  {
    printf("Error while freeing low memory block\n");
    exit(0);
  }
}

long low_memory_available()
{
  rminfo rm;
  memset(&rm,0,sizeof(rm));
  rm.eax=0x4800;
  rm.ebx=0xffff;        // try to allocate the maximum size, dos while tells us how much is possible
  RM_intr(0x21,&rm);
  if (rm.flags&1)  
    return rm.ebx*16;
  else                  // this shouldn't succed, but just in case...
  {
    free_low_memory((void *)((rm.eax&0xffff)<<4));
    return 0xffff*16;
  }
}