104 lines
2.5 KiB
Go
104 lines
2.5 KiB
Go
package core6502
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const (
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modeImplicit = iota + 1
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modeImplicitX
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modeImplicitY
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modeAccumulator
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modeImmediate
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modeZeroPage
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modeZeroPageX
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modeZeroPageY
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modeRelative
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modeAbsolute
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modeAbsoluteX
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modeAbsoluteY
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modeIndirect
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modeIndexedIndirectX
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modeIndirectIndexedY
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)
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func getWordInLine(line []uint8) uint16 {
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return uint16(line[1]) + 0x100*uint16(line[2])
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}
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func resolveValue(s *State, line []uint8, opcode opcode) uint8 {
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getValue, _, _ := resolve(s, line, opcode)
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return getValue()
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}
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func resolveGetSetValue(s *State, line []uint8, opcode opcode) (value uint8, setValue func(uint8)) {
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getValue, setValue, _ := resolve(s, line, opcode)
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value = getValue()
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return
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}
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func resolveSetValue(s *State, line []uint8, opcode opcode) func(uint8) {
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_, setValue, _ := resolve(s, line, opcode)
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return setValue
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}
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func resolveAddress(s *State, line []uint8, opcode opcode) uint16 {
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_, _, address := resolve(s, line, opcode)
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return address
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}
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func resolve(s *State, line []uint8, opcode opcode) (getValue func() uint8, setValue func(uint8), address uint16) {
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hasAddress := true
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register := regNone
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switch opcode.addressMode {
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case modeAccumulator:
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getValue = func() uint8 { return s.reg.getA() }
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hasAddress = false
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register = regA
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case modeImplicitX:
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getValue = func() uint8 { return s.reg.getX() }
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hasAddress = false
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register = regX
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case modeImplicitY:
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getValue = func() uint8 { return s.reg.getY() }
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hasAddress = false
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register = regY
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case modeImmediate:
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getValue = func() uint8 { return line[1] }
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hasAddress = false
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case modeZeroPage:
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address = uint16(line[1])
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case modeZeroPageX:
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address = uint16(line[1] + s.reg.getX())
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case modeZeroPageY:
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address = uint16(line[1] + s.reg.getY())
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case modeAbsolute:
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address = getWordInLine(line)
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case modeAbsoluteX:
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address = getWordInLine(line) + uint16(s.reg.getX())
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case modeAbsoluteY:
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address = getWordInLine(line) + uint16(s.reg.getY())
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case modeIndexedIndirectX:
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addressAddress := uint8(line[1] + s.reg.getX())
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address = getZeroPageWord(s.mem, addressAddress)
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case modeIndirect:
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addressAddress := getWordInLine(line)
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address = getWord(s.mem, addressAddress)
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case modeIndirectIndexedY:
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address = getZeroPageWord(s.mem, line[1]) +
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uint16(s.reg.getY())
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}
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if hasAddress {
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getValue = func() uint8 { return s.mem.Peek(address) }
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}
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setValue = func(value uint8) {
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if hasAddress {
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s.mem.Poke(address, value)
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} else if register != regNone {
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s.reg.setRegister(register, value)
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} else {
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panic("Assert failed. Should never happen")
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}
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}
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return
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}
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