Пишем CHIP-8 эмулятор с использованием Rust и WebAssembly (часть 2)

static mut CPU: Cpu = Cpu {
    memory: [0; 4096],
    // other fields go here …
}
 
#[no_mangle]
pub fn get_memory() -> &'static [u8; 4096] {
    unsafe {
        &CPU.memory
    }
}

const instance = await WebAssembly.instantiate(module);
const exports = instance.exports;
 
const programMemory = new Uint8Array(
  exports.memory.buffer,
  exports.get_memory(),
  4096
);

fetch(`roms/${rom}`)
  .then(i => i.arrayBuffer())
  .then(buffer => {
    const rom = new DataView(buffer, 0, buffer.byteLength);
    exports.reset();
    for (i = 0; i < rom.byteLength; i++) {
      programMemory[0x200 + i] = rom.getUint8(i);
    }
  });

fn process_opcode(&mut self, opcode: u16) {
    match (opcode) {
        0x1000 ... 0x1FFF => self.pc = opcode & 0x0FFF,
        // match other ranges to process other opcodes.
        _ => ()
    }
}

fn process_opcode(&mut self, opcode: u16) {
    match (opcode) {
        0x1000 ... 0x1FFF => self.pc = opcode & 0x0FFF,
        // ...
        0x8000 ... 0x8FFF => {
            match opcode & 0x00F {
                // LD Vx, Vy
                0x0 => self.v[x] = self.v[y],
                // OR Vx, Vy
                0x1 => self.v[x] = self.v[x] | self.v[y],
                // …
             }
        // ...
        _ => ()
    }
}

// break up into nibbles
let op_1 = (opcode & 0xF000) >> 12;
let op_2 = (opcode & 0x0F00) >> 8;
let op_3 = (opcode & 0x00F0) >> 4;
let op_4 = opcode & 0x000F;
 
match (op_1, op_2, op_3, op_4) {
    // CLS
    (0, 0, 0xE, 0) => self.display.cls(),
    // JP
    (0x1, _, _, _) => self.pc = nnn,
    // LD Vx, Vy
    (0x8, _, _, 0x0) => self.v[x] = self.v[y],
    // OR Vx, Vy
    (0x8, _, _, 0x1) => self.v[x] = self.v[x] | self.v[y],
    // AND Vx, Vy
    (0x8, _, _, 0x2) => self.v[x] = self.v[x] & self.v[y],
    // LD F, Vx
    (0xF, _, 0x2, 0x9) => self.i = vx as u16 * 5,
    // ...
    (_, _, _, _) => ()
}

(0x8, x, y, 0x0) => self.v[x as usize] = self.v[y as usize]

let x = ((opcode & 0x0F00) >> 8) as usize;
let y = ((opcode & 0x00F0) >> 4) as usize;
let vx = self.v[x];
let vy = self.v[y];
let nnn = opcode & 0x0FFF;
let kk = (opcode & 0x00FF) as u8;
let n = (opcode & 0x000F) as u8;