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FruitMachine-Swift
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sbc notes

This commit is contained in:
Luigi Thirty 2017-08-02 04:07:19 -04:00
parent 4efe09ad30
commit 5e6ae41c86
1 changed files with 4 additions and 1 deletions
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5
FruitMachine/M6502/Opcodes/Opcodes.swift
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@ -167,6 +167,7 @@ final class Opcodes: NSObject {
static func SBC(state: CPU, addressingMode: CPU.AddressingMode) -> Void {
let operand = UInt8(getOperandByteForAddressingMode(state: state, mode: addressingMode))
//I don't think this 16-bit calculation is working right
var t16: UInt16 = UInt16(state.accumulator &- operand) &- UInt16((state.status_register.carry ? UInt8(0) : UInt8(1)))
let t8: UInt8 = UInt8(t16 & 0xFF)
@ -175,8 +176,10 @@ final class Opcodes: NSObject {
if(state.status_register.decimal == true) {
t16 = UInt16(hex2bcd(hex: state.accumulator) + hex2bcd(hex: operand) + (state.status_register.carry ? UInt8(1) : UInt8(0)))
} else {
state.status_register.carry = (t16 >> 8) == 0
//carry flag isn't being set properly
state.status_register.carry = (t8 >= 127) ? true : false
//let signed = Int8(bitPattern: t8)
//state.status_register.carry = ((-128 > signed) || (127 < signed)) ? true : false
}
state.accumulator = t8