//----------------------------------------------------------------------
//
//	MemoryGetOperandAddress
//
//	This routine takes an instruction and a pointer to a PCB, and
//	returns the address that the instruction is trying to use
//	for its memory operand.  If the instruction doesn't access memory,
//	it returns 0xffffffff.
//
//----------------------------------------------------------------------
uint32
MemoryGetOperandAddress (PCB *pcb, uint32 instr)
{
  static uint32	invalidOps = 0x3404;
  uint32	opcode = (instr >> 26) & 0x3f;
  uint32	reg;
  uint32	addr;
  uint32	offset;

  if ((opcode<0x20) || (opcode>0x2f) || ((invalidOps >> (opcode-0x20)) & 1)) {
    return (0xffffffff);
  }
  reg = (instr >> 21) & 0x1f;
  offset = instr & 0xffff;
  if (offset & 0x8000) {
    offset |= 0xffff0000;
  }
  addr = pcb->registers[reg] + offset;
  dbprintf ('m', "Operand for instruction %08x is 0x%x (reg=<%d,0x%x>)\n",
	    instr, addr, reg, pcb->registers[reg]);
  return (addr);
}