63 lines
1.3 KiB
Kotlin
63 lines
1.3 KiB
Kotlin
package android.emu6502.instructions.impl
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import android.emu6502.CPU
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import android.emu6502.instructions.BaseInstruction
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import android.emu6502.instructions.Instruction
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/** SuBtract with Carry */
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class SBC(private val cpu: CPU) : BaseInstruction(Instruction.SBC, cpu.instructionList) {
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override fun immediate() {
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testSBC(cpu.popByte())
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}
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private fun testSBC(value: Int) {
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if (cpu.A.xor(value).and(0x80) != 0) {
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cpu.setOverflow()
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} else {
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cpu.CLV()
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}
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var w: Int
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if (cpu.decimalMode()) {
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var tmp = 0xf + cpu.A.and(0xf) - value.and(0xf) + cpu.P.and(1)
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if (tmp < 0x10) {
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w = 0
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tmp -= 6
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} else {
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w = 0x10
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tmp -= 0x10
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}
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w += 0xf0 + cpu.A.and(0xf0) - value.and(0xf0)
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if (w < 0x100) {
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cpu.CLC()
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if (cpu.overflow() && w < 0x80) {
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cpu.CLV()
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}
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w -= 0x60
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} else {
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cpu.SEC()
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if (cpu.overflow() && w >= 0x180) {
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cpu.CLV()
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}
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}
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w += tmp
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} else {
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w = 0xff + cpu.A - value + cpu.P.and(1)
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if (w < 0x100) {
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cpu.CLC()
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if (cpu.overflow() && w < 0x80) {
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cpu.CLV()
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}
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} else {
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cpu.SEC()
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if (cpu.overflow() && w >= 0x180) {
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cpu.CLV()
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}
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}
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}
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cpu.A = w.and(0xff)
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cpu.setSZFlagsForRegA()
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}
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}
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