From 35bdeac2c81aaf2fda3b1881701ba0367bbefc1b Mon Sep 17 00:00:00 2001
From: Bradford Lamson-Scribner <brad.lamson@gmail.com>
Date: Sat, 30 May 2020 17:14:13 -0600
Subject: [PATCH] internal/vm/{exec_funcs,opcodes}: handle INX instruction
 execution

---
 internal/vm/exec_funcs.go | 34 ++++++++++++++++++++++++++++------
 internal/vm/opcodes.go    | 20 ++++++++++----------
 2 files changed, 38 insertions(+), 16 deletions(-)

diff --git a/internal/vm/exec_funcs.go b/internal/vm/exec_funcs.go
index b36b3a9..55607b5 100644
--- a/internal/vm/exec_funcs.go
+++ b/internal/vm/exec_funcs.go
@@ -9,7 +9,7 @@ func todo(a *Appleone, o op) error {
 
 // interrupt,                       N Z C I D V
 // push PC+2, push SR               - - - 1 - -
-func exec0x00(a *Appleone, o op) error {
+func execBRK(a *Appleone, o op) error {
 	// set processer status flag to BRK
 	a.cpu.ps = flagBreak
 
@@ -24,7 +24,7 @@ func exec0x00(a *Appleone, o op) error {
 
 // pull SR, pull PC                 N Z C I D V
 // from stack
-func exec0x40(a *Appleone, o op) error {
+func execRTI(a *Appleone, o op) error {
 	a.cpu.ps = a.popStackWord()
 	a.cpu.pc = a.popStackDWord()
 	return nil
@@ -32,18 +32,40 @@ func exec0x40(a *Appleone, o op) error {
 
 // M - 1 -> M                       N Z C I D V
 //                                  + + - - - -
-func exec0xC6(a *Appleone, o op) error {
+func execDEC(a *Appleone, o op) error {
 	addr, err := o.getAddr(a)
 	if err != nil {
 		return err
 	}
-
 	b := a.mem[addr]
 	b--
 	a.mem[addr] = b
-
 	a.setZeroIfNeeded(b)
 	a.setNegativeIfOverflow(b)
-
+	return nil
+}
+
+// M + 1 -> M                       N Z C I D V
+//                                  + + - - - -
+func execINC(a *Appleone, o op) error {
+	addr, err := o.getAddr(a)
+	if err != nil {
+		return err
+	}
+	b := a.mem[addr]
+	b++
+	a.mem[addr] = b
+	a.setZeroIfNeeded(b)
+	a.setNegativeIfOverflow(b)
+	return nil
+}
+
+// X + 1 -> X                       N Z C I D V
+//                                  + + - - - -
+func execINX(a *Appleone, o op) error {
+	b := a.cpu.x + 1
+	a.cpu.x = b
+	a.setZeroIfNeeded(b)
+	a.setNegativeIfOverflow(b)
 	return nil
 }
diff --git a/internal/vm/opcodes.go b/internal/vm/opcodes.go
index 4ee105e..1601278 100644
--- a/internal/vm/opcodes.go
+++ b/internal/vm/opcodes.go
@@ -77,13 +77,13 @@ var opcodes = map[uint8]op{
 	// addressing    assembler    opc  bytes  cyles
 	// --------------------------------------------
 	// implied       BRK          00   1      7
-	0x00: newOp("BRK", 0x00, 1, implied, exec0x00),
+	0x00: newOp("BRK", 0x00, 1, implied, execBRK),
 
 	// RTI Return from Interrupt
 	// addressing    assembler    opc  bytes  cyles
 	// --------------------------------------------
 	// implied       RTI          40   1      6
-	0x40: newOp("RTI", 0x40, 1, implied, exec0x40),
+	0x40: newOp("RTI", 0x40, 1, implied, execRTI),
 
 	// DEC Decrement Memory by One
 	// addressing    assembler    opc  bytes  cyles
@@ -92,10 +92,10 @@ var opcodes = map[uint8]op{
 	// zeropage,X    DEC oper,X   D6   2      6
 	// absolute      DEC oper     CE   3      6
 	// absolute,X    DEC oper,X   DE   3      7
-	0xC6: newOp("DEC", 0xC6, 2, zeroPage, exec0xC6),
-	0xD6: newOp("DEC", 0xD6, 2, zeroPageXIndexed, exec0xC6),
-	0xCE: newOp("DEC", 0xCE, 3, absolute, exec0xC6),
-	0xDE: newOp("DEC", 0xDE, 3, absoluteXIndexed, exec0xC6),
+	0xC6: newOp("DEC", 0xC6, 2, zeroPage, execDEC),
+	0xD6: newOp("DEC", 0xD6, 2, zeroPageXIndexed, execDEC),
+	0xCE: newOp("DEC", 0xCE, 3, absolute, execDEC),
+	0xDE: newOp("DEC", 0xDE, 3, absoluteXIndexed, execDEC),
 
 	// INC Increment Memory by One
 	// addressing    assembler    opc  bytes  cyles
@@ -104,10 +104,10 @@ var opcodes = map[uint8]op{
 	// zeropage,X    INC oper,X   F6   2      6
 	// absolute      INC oper     EE   3      6
 	// absolute,X    INC oper,X   FE   3      7
-	0xE6: newOp("INC", 0xE6, 2, zeroPage, todo),
-	0xF6: newOp("INC", 0xF6, 2, zeroPageXIndexed, todo),
-	0xEE: newOp("INC", 0xEE, 3, absolute, todo),
-	0xFE: newOp("INC", 0xFE, 3, absoluteXIndexed, todo),
+	0xE6: newOp("INC", 0xE6, 2, zeroPage, execINC),
+	0xF6: newOp("INC", 0xF6, 2, zeroPageXIndexed, execINC),
+	0xEE: newOp("INC", 0xEE, 3, absolute, execINC),
+	0xFE: newOp("INC", 0xFE, 3, absoluteXIndexed, execINC),
 
 	// INX Increment Index X by One
 	// addressing    assembler    opc  bytes  cyles