From b41f50f447dee06b0753d524a824f776b51034d4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bel=C3=A9n=20Albeza?= <belen@hey.com>
Date: Sun, 28 Jul 2024 10:02:35 +0200
Subject: [PATCH] Implement Jump Offset opcode

---
 chip8/src/vm.rs        | 18 ++++++++++++++++++
 chip8/src/vm/opcode.rs |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/chip8/src/vm.rs b/chip8/src/vm.rs
index a68f350..2b5b5f3 100644
--- a/chip8/src/vm.rs
+++ b/chip8/src/vm.rs
@@ -82,6 +82,7 @@ impl Vm {
             Opcode::SubN(x, y) => self.exec_subn_vy_vx(x, y)?,
             Opcode::ShiftL(x, y) => self.exec_shift_left(x, y)?,
             Opcode::LoadI(addr) => self.exec_load_i(addr)?,
+            Opcode::JumpOffset(addr) => self.exec_jump_offset(addr)?,
             Opcode::Display(x, y, rows) => self.exec_display(x, y, rows)?,
             Opcode::NoOp => {}
             _ => todo!(),
@@ -259,6 +260,11 @@ impl Vm {
 
         Ok(())
     }
+
+    fn exec_jump_offset(&mut self, addr: u16) -> Result<()> {
+        self.pc = addr + self.v_registers[0x0] as u16;
+        Ok(())
+    }
 }
 
 #[cfg(test)]
@@ -597,4 +603,16 @@ mod tests {
         assert_eq!(vm.v_registers[0x0], 0x02);
         assert_eq!(vm.v_registers[0xf], 0x01);
     }
+
+    #[test]
+    fn opcode_jump_offset() {
+        let rom = [0xb2, 0x00];
+        let mut vm = Vm::new(&rom);
+        vm.v_registers[0x0] = 0xab;
+
+        let res = vm.tick();
+
+        assert!(res.is_ok());
+        assert_eq!(vm.pc, 0x2ab);
+    }
 }
diff --git a/chip8/src/vm/opcode.rs b/chip8/src/vm/opcode.rs
index 73e010d..d8804d9 100644
--- a/chip8/src/vm/opcode.rs
+++ b/chip8/src/vm/opcode.rs
@@ -22,6 +22,7 @@ pub enum Opcode {
     SubN(u8, u8),
     ShiftL(u8, u8),
     LoadI(u16),
+    JumpOffset(u16),
     Display(u8, u8, u8),
 }
 
@@ -58,6 +59,7 @@ impl TryFrom<u16> for Opcode {
             (0x8, x, y, 0x7) => Ok(Self::SubN(x, y)),
             (0x8, x, y, 0xe) => Ok(Self::ShiftL(x, y)),
             (0xa, _, _, _) => Ok(Self::LoadI(nnn)),
+            (0xb, _, _, _) => Ok(Self::JumpOffset(nnn)),
             (0xd, x, y, n) => Ok(Self::Display(x, y, n)),
             _ => Err(VmError::InvalidOpcode(value)),
         }
@@ -88,6 +90,7 @@ mod tests {
         assert_eq!(Opcode::try_from(0x8ab7), Ok(Opcode::SubN(0xa, 0xb)));
         assert_eq!(Opcode::try_from(0x8abe), Ok(Opcode::ShiftL(0xa, 0xb)));
         assert_eq!(Opcode::try_from(0xaabc), Ok(Opcode::LoadI(0x0abc)));
+        assert_eq!(Opcode::try_from(0xbabc), Ok(Opcode::JumpOffset(0x0abc)));
         assert_eq!(Opcode::try_from(0xdabc), Ok(Opcode::Display(0xa, 0xb, 0xc)));
     }
 }