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reimplemented CMP, CPX and CPY based on 2006/2007 code

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James Tauber 2011-08-06 22:39:11 -04:00
parent 6fb2d79cda
commit 84bdef67cd
1 changed files with 9 additions and 12 deletions
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applepy.py
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@ -639,22 +639,19 @@ class CPU:
# COMPARISON # COMPARISON
def CMP(self, operand_address): def CMP(self, operand_address):
value = self.memory.read_byte(operand_address) result = self.accumulator - self.memory.read_byte(operand_address)
self.carry_flag = (self.accumulator >= value) self.carry_flag = (result >= 0)
self.zero_flag = (self.accumulator == value) self.update_nz(result)
self.sign_flag = (self.accumulator < 0x80) # @@@ is this right?
def CPX(self, operand_address): def CPX(self, operand_address):
value = self.memory.read_byte(operand_address) result = self.x_index - self.memory.read_byte(operand_address)
self.carry_flag = (self.x_index >= value) self.carry_flag = (result >= 0)
self.zero_flag = (self.x_index == value) self.update_nz(result)
self.sign_flag = (self.x_index < 0x80) # TODO: is this right?
def CPY(self, operand_address): def CPY(self, operand_address):
value = self.memory.read_byte(operand_address) result = self.y_index - self.memory.read_byte(operand_address)
self.carry_flag = (self.y_index >= value) self.carry_flag = (result >= 0)
self.zero_flag = (self.y_index == value) self.update_nz(result)
self.sign_flag = (self.y_index < 0x80) # @@@ is this right?
# SYSTEM # SYSTEM