[zvm commit] r204 - trunk/zvm

[codesite...@google.com]

Author: david.jc.anderson
Date: Sat Jun 21 14:48:03 2008
New Revision: 204

Modified:
trunk/zvm/zcpu.py

Log:
Fix the implementation of op_jump to jump to the correct offset.

Modified: trunk/zvm/zcpu.py
==============================================================================
--- trunk/zvm/zcpu.py (original)
+++ trunk/zvm/zcpu.py Sat Jun 21 14:48:03 2008
@@ -155,8 +155,8 @@
them around, and brings the magic to your screen!"""
log("Execution started")
while True:
- log("Next opcode")
current_pc = self._opdecoder.program_counter
+ log("Next opcode %x" % current_pc)
(opcode_class, opcode_number,
operands) = self._opdecoder.get_next_instruction()
implemented, func = self._get_handler(opcode_class,
@@ -343,11 +343,16 @@
def op_ret(self, *args):
"""TODO: Write docstring here."""

- def op_jump(self, *args):
+ def op_jump(self, offset):
"""Jump unconditionally to the given branch offset. This
opcode does not follow the usual branch decision algorithm,
and so we do not call the _branch method to dispatch the call."""
- cond, offset = self._opdecoder.get_branch_offset()
+ # The offset to the jump instruction is known to be a 2-byte
+ # signed integer. We need to make it signed before applying
+ # the offset.
+ if (offset >= 2**15):
+ offset = - 2**16 + offset
+ log("Jump unconditionally to offset %d" % offset)
self._opdecoder.program_counter += (offset - 2)