Tenyr simulator in Javascript

tenyr.js

var tenyr = (function() {
  "use strict";

  var regbuf = new ArrayBuffer(4 * 16);
  var regs   = new Int32Array(regbuf);
  var mem    = {};
  var hooks  = [];

  var add_hook = function(hook) {
    hooks.push(hook);
  }

  var put = function(addr, word) {
    for(var i = 0; i < hooks.length; ++i)
      if(addr >= hooks[i].min && addr <= hooks[i].max && hooks[i].fn(0, addr, word))
        return;

    mem[addr] = word;
  };

  var get = function(addr) {
    for(var i = 0; i < hooks.length; ++i)
      if(addr >= hooks[i].min && addr <= hooks[i].max && hooks[i].fn(1, addr, word))
        return;

    if(typeof mem[addr] !== 'undefined')
      return mem[addr];
    return 0;
  };

  var op = function(idx, x, y) {
    switch(idx) {
      case 0:  return x | y;
      case 1:  return x & y;
      case 2:  return x + y;
      case 3:  return x * y;
      case 5:  return x << y;
      case 6:  return 0 - ((x ^ 0x80000000) < (y ^ 0x80000000));
      case 7:  return 0 - (x == y);
      case 8:  return 0 - ((x ^ 0x80000000) > (y ^ 0x80000000));
      case 9:  return x & ~y;
      case 10: return x ^ y;
      case 11: return x - y;
      case 12: return x ^ ~y;
      case 13: return x >> y;
      case 14: return 0 - (x != y);
    }
  };

  var step = function() {
    var word = get(regs[15]++);

    if(word == 0xffffffff)
      return false;

    var imm = word & 0xfff;
    imm = imm | (0xfffff800 * ((imm >> 11) & 1));

    var i = {
      p    : (word >> 30) & 0x3,
      dd   : (word >> 28) & 0x3,
      z    : (word >> 24) & 0xf,
      x    : (word >> 20) & 0xf,
      y    : (word >> 16) & 0xf,
      op   : (word >> 12) & 0xf,
      imm  : imm
    };

    if(i.p)
      var expr = op(i.op, regs[i.x], i.imm) + regs[i.y];
    else
      var expr = op(i.op, regs[i.x], regs[i.y]) + i.imm;

    switch(i.dd) {
      case 0: regs[i.z]      = expr;      break;
      case 1: regs[i.z]      = get(expr); break;
      case 2: put(regs[i.z], expr);       break;
      case 3: put(expr, regs[i.z]);       break;
    }

    return true;
  };

  var run = function(bytes) {
    for(var i = 0; i < regs.length; ++i)
      regs[i] = 0;
    regs[15] = 0x1000;

    for(var i = 0; i < bytes.length; ++i)
      mem[0x1000 + i] = bytes[i];

    while(step());
    return regs;
  };

  return {
    add : add_hook,
    run : run
  };
})();