From 7d14568e447ddadcf3d5cbffa259974311aa320c Mon Sep 17 00:00:00 2001
From: Adam Eury <euryadam@gmail.com>
Date: Sun, 14 Jan 2024 22:51:23 -0500
Subject: [PATCH] Add DECX instruction

---
 examples/factorial.g |  2 +-
 gmachine.go          |  4 ++++
 gmachine_test.go     | 14 ++++++++++++++
 testdata/gc.txtar    |  4 ++--
 token/token.go       |  1 +
 token/token_test.go  |  1 +
 6 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/examples/factorial.g b/examples/factorial.g
index b4a0f2f..79c6dc6 100644
--- a/examples/factorial.g
+++ b/examples/factorial.g
@@ -1,6 +1,6 @@
 ; Tasks:
 ; 1. Implement MULA - done
-; 2. Implement SETX
+; 2. Implement SETX - done
 ; 3. Implement DECX (and DECA, DECY)
 ; 4. Implement JXNZ
 ; 5. Implement CALL and RTRN
diff --git a/gmachine.go b/gmachine.go
index 376a667..8bea67a 100644
--- a/gmachine.go
+++ b/gmachine.go
@@ -25,6 +25,7 @@ const (
 	OpOUTA
 	OpINCA
 	OpDECA
+	OpDECX
 	OpADDA
 	OpMULA
 	OpMOVA
@@ -66,6 +67,7 @@ var opcodes = map[string]Word{
 	"OUTA": OpOUTA,
 	"INCA": OpINCA,
 	"DECA": OpDECA,
+	"DECX": OpDECX,
 	"ADDA": OpADDA,
 	"MULA": OpMULA,
 	"MOVA": OpMOVA,
@@ -130,6 +132,8 @@ func (g *Machine) Run() {
 			g.A++
 		case OpDECA:
 			g.A--
+		case OpDECX:
+			g.X--
 		case OpADDA:
 			switch g.Next() {
 			case RegX:
diff --git a/gmachine_test.go b/gmachine_test.go
index c6a07a1..5dffca0 100644
--- a/gmachine_test.go
+++ b/gmachine_test.go
@@ -143,6 +143,20 @@ func TestDECA(t *testing.T) {
 	}
 }
 
+func TestDECX(t *testing.T) {
+	t.Parallel()
+	g := gmachine.New(nil)
+	g.X = 1
+	var wantX gmachine.Word = 0
+	err := assembleAndRunFromString(g, "DECX")
+	if err != nil {
+		t.Fatal("didn't expect an error", err)
+	}
+	if wantX != g.X {
+		t.Errorf("want X value %d, got %d", wantX, g.X)
+	}
+}
+
 func TestSETA(t *testing.T) {
 	t.Parallel()
 	g := gmachine.New(nil)
diff --git a/testdata/gc.txtar b/testdata/gc.txtar
index 273d5c9..f3ff2ea 100644
--- a/testdata/gc.txtar
+++ b/testdata/gc.txtar
@@ -9,6 +9,6 @@ SETA 42
 OUTA
 
 -- want --
-0000000 0000 0000 0000 0900 0000 0000 0000 2a00
+0000000 0000 0000 0000 0a00 0000 0000 0000 2a00
 0000010 0000 0000 0000 0300                    
-0000018
\ No newline at end of file
+0000018
diff --git a/token/token.go b/token/token.go
index c3bb7f5..8ad9979 100644
--- a/token/token.go
+++ b/token/token.go
@@ -24,6 +24,7 @@ var opcodes = map[string]TokenType{
 	"OUTA": OPCODE,
 	"INCA": OPCODE,
 	"DECA": OPCODE,
+	"DECX": OPCODE,
 	"ADDA": OPCODE,
 	"MULA": OPCODE,
 	"MOVA": OPCODE,
diff --git a/token/token_test.go b/token/token_test.go
index b90c604..587c888 100644
--- a/token/token_test.go
+++ b/token/token_test.go
@@ -16,6 +16,7 @@ func TestLookupIdent(t *testing.T) {
 		{"OUTA", token.OPCODE},
 		{"INCA", token.OPCODE},
 		{"DECA", token.OPCODE},
+		{"DECX", token.OPCODE},
 		{"ADDA", token.OPCODE},
 		{"MULA", token.OPCODE},
 		{"MOVA", token.OPCODE},