def _resolve(self, uref):
"""
Resolve the given unresolved reference. Get the symbol's value or
re-evaluate an expression and place that value in the reference's
address.
"""
if uref.expr is None:
value = self.meta.lookup(uref.ref)
else:
value = uref.expr.eval(self.meta)
if uref.type == REFERENCE_VALUE:
self.mem[uref.address] = vm.size8(value)
elif uref.type == REFERENCE_ABSOLUTE:
self.mem[uref.address::2] = vm.size16(value)
elif uref.type == REFERENCE_ZERO_PAGE:
self.mem[uref.address] = vm.size8(value)
elif uref.type == REFERENCE_RELATIVE:
abs_address = vm.size16(value)
# Branch is relative to PC after opcode and displacement
# have been consumed. Since abs_address points to where
# the displacement should go, add one to this value.
rel_address = abs_address - (uref.address + 1)
assert_branch_displacement(rel_address)
self.mem[uref.address] = vm.twos_forward(rel_address)
else:
assert False
def test_twos_forward_max_unsigned(self):
self.assertEquals(0xff, vm.twos_forward(255))
def test_twos_forward_min_signed(self):
self.assertEquals(0x80, vm.twos_forward(-128))
def test_twos_forward_max_signed(self):
self.assertEquals(0x7f, vm.twos_forward(127))
def test_twos_forward_negative(self):
self.assertEquals(0xfe, vm.twos_forward(-2))
def test_twos_forward(self):
self.assertEquals(0x02, vm.twos_forward(2))