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Simplify and clean up

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kris 2019-08-20 21:17:33 +01:00
parent 3d30544b95
commit 3468cdce1c
1 changed files with 16 additions and 32 deletions
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48
py65/devices/mpu6502.py
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@ -446,47 +446,31 @@ class MPU:
See e.g. http://6502.org/tutorials/decimal_mode.html#A for details
"""
data = self.ByteAt(x())
#
# halfcarry = 1
decimalcarry = 0
# adjust0 = 0
# adjust1 = 0
#
# nibble0 = (self.a & 0xf) + (~data & 0xf) + (self.p & self.CARRY)
# if nibble0 <= 0xf:
# halfcarry = 0
# adjust0 = 10 # -0x6
# nibble1 = ((self.a >> 4) & 0xf) + ((~data >> 4) & 0xf) + halfcarry
# if nibble1 <= 0xf:
# adjust1 = 10 << 4 # -0x60
# the ALU outputs are not yet decimally adjusted
aluresult = self.a + (~data & self.byteMask) + (self.p & self.CARRY)
if aluresult > self.byteMask:
decimalcarry = 1
decimalcarry = aluresult > self.byteMask
aluresult &= self.byteMask
AL = (self.a & 0xf) - (data & 0xf) + (self.p & self.CARRY) - 1
al = (self.a & 0xf) - (data & 0xf) + (self.p & self.CARRY) - 1
if flags_use_adjusted_result: # Note: 65C02 but not 65816
A = self.a - data + (self.p & self.CARRY) - 1
assert (A & self.byteMask) == aluresult
if flags_use_adjusted_result: # 65C02 but not 65816
a = self.a - data + (self.p & self.CARRY) - 1
if a < 0:
a -= 0x60
if al < 0:
a -= 0x6
if A < 0:
A -= 0x60
else: # 6502
# Note: 65816 apparently also uses this logic instead of 65C02
if al < 0:
al = ((al - 0x6) & 0xf) - 0x10
a = (self.a & 0xf0) - (data & 0xf0) + al
if a < 0:
a -= 0x60
if AL < 0:
A -= 0x6
else:
# Note: 65816 apparently uses this logic instead of 65C02
if AL < 0:
AL = ((AL - 0x6) & 0xf) - 0x10
A = (self.a & 0xf0) - (data & 0xf0) + AL
if A < 0:
A -= 0x60
adjresult = A & self.byteMask
adjresult = a & self.byteMask
if flags_use_adjusted_result: # 65C02 and 65816
# Z and N use adjusted (i.e. decimal) result