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simplify calculating signed values in adc and sbc

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This commit is contained in:
Greg Hewgill 2011-08-07 18:33:42 +12:00
parent 5a8b25b771
commit e961d7e00d
1 changed files with 8 additions and 12 deletions
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applepy.py
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@ -602,12 +602,10 @@ class CPU:
# @@@ doesn't handle BCD yet
assert not self.decimal_mode_flag
a1 = a2 = self.accumulator
if a1 & 0x80:
a1 = (a1 & 0x7F) - 0x80
m1 = m2 = self.memory.read_byte(operand_address)
if m1 & 0x80:
m1 = (m1 & 0x7F) - 0x80
a2 = self.accumulator
a1 = signed(a2)
m2 = self.memory.read_byte(operand_address)
m1 = signed(m2)
# twos complement addition
result1 = a1 + m1 + self.carry_flag
@ -624,12 +622,10 @@ class CPU:
# @@@ doesn't handle BCD yet
assert not self.decimal_mode_flag
a1 = a2 = self.accumulator
if a1 & 0x80:
a1 = (a1 & 0x7F) - 0x80
m1 = m2 = self.memory.read_byte(operand_address)
if m1 & 0x80:
m1 = (m1 & 0x7F) - 0x80
a2 = self.accumulator
a1 = signed(a2)
m2 = self.memory.read_byte(operand_address)
m1 = signed(m2)
# twos complement subtraction
result1 = a1 - m1 - [1, 0][self.carry_flag]