From 3b05332d28a82136afc32d1dad30b34482305244 Mon Sep 17 00:00:00 2001
From: Roman Boykov <romychs@gmail.com>
Date: Wed, 15 Apr 2026 15:57:33 +0300
Subject: [PATCH] fix relative jump disasm

---
 dis/z80disasm.go      |  4 ++--
 dis/z80disasm_test.go | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/dis/z80disasm.go b/dis/z80disasm.go
index 8de81de..3a2bdc1 100644
--- a/dis/z80disasm.go
+++ b/dis/z80disasm.go
@@ -39,12 +39,12 @@ func (d *Disassembler) jp(op, cond string) string {
 }
 
 func (d *Disassembler) jr(op, cond string) string {
-	addr := d.pc
+	addr := d.pc + 1
 	offset := d.getByte()
 	if offset&0x80 != 0 {
 		addr += 0xFF00 | uint16(offset)
 	} else {
-		addr += d.pc + uint16(offset)
+		addr += uint16(offset)
 	}
 	if cond != "" {
 		cond += sep
diff --git a/dis/z80disasm_test.go b/dis/z80disasm_test.go
index c3dd5cb..b7be457 100644
--- a/dis/z80disasm_test.go
+++ b/dis/z80disasm_test.go
@@ -90,3 +90,25 @@ func Test_JP_nn(t *testing.T) {
 		t.Errorf("Error disassm JP nn, result '%s', expected '%s'", res, expected)
 	}
 }
+
+var testJRf = []byte{0x28, 0x09} // JR Z,+9
+
+func Test_JR_Z_nn(t *testing.T) {
+	expected := "  31EF JR Z, 0x31FA" // PC+2+9
+	setMemory(0x31EF, testJRf)
+	res := disasm.Disassm(0x31EF)
+	if res != expected {
+		t.Errorf("Error disassm JR Z,nn, result '%s', expected '%s'", res, expected)
+	}
+}
+
+var testJRb = []byte{0x18, 0xf1} // JR Z,+9
+
+func Test_JR_mnn(t *testing.T) {
+	expected := "  31F8 JR 0x31EB" // JR back
+	setMemory(0x31F8, testJRb)
+	res := disasm.Disassm(0x31F8)
+	if res != expected {
+		t.Errorf("Error disassm JR -nn, result '%s', expected '%s'", res, expected)
+	}
+}