snes/snes-core/src/cpu/instructions/bvs.rs

use crate::cpu::{bus::Bus, registers::Registers};

use super::CPUInstruction;
use super::decoder_common;
use super::branch_common;

static INSTR_NAME: &'static str = "BVS";

pub struct BVS {}

impl CPUInstruction for BVS {
    fn execute(&self, registers: &mut Registers, bus: &mut Bus) {
        branch_common::do_branch_instr(registers, bus, registers.get_overflow_flag());
    }

    fn mnemonic(&self, registers: &Registers, bus: &Bus, opcode: u8) -> String {
        decoder_common::mnemonic_branch_nearlabel(opcode, INSTR_NAME, registers, bus)
    }
}


#[cfg(test)]
mod cpu_instructions_tests {
    use super::*;

    #[test]
    fn test() {
        let instruction = BVS{};
        // test with positive nearlabel
        // branch not taken
        let mut registers = Registers::new();
        let mut bus = Bus::new();
        registers.pc = 0x0000;
        registers.cycles = 0;
        registers.set_overflow_flag(false);
        bus.write(0x02, 0b00001111);
        instruction.execute(&mut registers, &mut bus);
        assert_eq!(registers.pc, 0x02);
        assert_eq!(registers.cycles, 2);
        // branch taken
        registers.pc = 0x0000;
        registers.cycles = 0;
        registers.set_overflow_flag(true);
        bus.write(0x01, 0b00001111);
        instruction.execute(&mut registers, &mut bus);
        assert_eq!(registers.pc, 0x02 + 0b00001111);
        assert_eq!(registers.cycles, 3);
        // test with negative nearlabel and boundary cross
        registers.pc = 0x0100;
        registers.cycles = 0;
        registers.set_overflow_flag(true);
        bus.write(0x101, 0xFB); // write -5
        instruction.execute(&mut registers, &mut bus);
        assert_eq!(registers.pc, 0xFD);
        assert_eq!(registers.cycles, 4);
    }
}