implement jr_nz

src/instructions/jmp.rs

@@ -8,6 +8,16 @@ pub fn jmp_a16() -> impl Fn(&mut CPU) {
     }
 }
 
+pub fn jr_nz() -> impl Fn(&mut CPU) {
+    move |cpu: &mut CPU| {
+        if !cpu.registers.f.zero {
+            return;
+        }
+        let offset = cpu.bus.memory[cpu.pc as usize];
+        cpu.pc = cpu.pc.wrapping_add(offset as i8 as u16);
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -20,4 +30,34 @@ mod tests {
         jmp_a16()(&mut cpu);
         assert_eq!(cpu.pc, 0x0201);
     }
+
+    #[test]
+    fn test_jr_nz_flag_unset() {
+        let mut cpu = CPU::default();
+        cpu.pc = 0x1000;
+        cpu.registers.f.zero = false;
+        cpu.bus.memory[0x1000] = 0x01;
+        jr_nz()(&mut cpu);
+        assert_eq!(cpu.pc, 0x1000);
+    }
+
+    #[test]
+    fn test_jr_nz_flag_set() {
+        let mut cpu = CPU::default();
+        cpu.pc = 0x1000;
+        cpu.registers.f.zero = true;
+        cpu.bus.memory[0x1000] = 0x05;
+        jr_nz()(&mut cpu);
+        assert_eq!(cpu.pc, 0x1005);
+    }
+
+    #[test]
+    fn test_jr_nz_flag_set_signed_negative() {
+        let mut cpu = CPU::default();
+        cpu.pc = 0x1000;
+        cpu.registers.f.zero = true;
+        cpu.bus.memory[0x1005] = -5i8 as u8;
+        jr_nz()(&mut cpu);
+        assert_eq!(cpu.pc, 0x1000);
+    }
 }

src/instructions/mod.rs

@@ -30,6 +30,8 @@ pub fn from_byte(byte: u8) -> Box<dyn Fn(&mut CPU)> {
         0x2C => Box::new(inc::inc_r(RegisterTarget::L)),
         0x3C => Box::new(inc::inc_r(RegisterTarget::A)),
 
+        0x20 => Box::new(jmp::jr_nz()),
+
         0x21 => Box::new(ld::ld_d16_u16(Register16bTarget::HL)),
         0x06 => Box::new(ld::ld_d8_u8(RegisterTarget::B)),
         0x16 => Box::new(ld::ld_d8_u8(RegisterTarget::B)),