simulator for a particular machine with a single operation

gistfile1.js

// http://jsfiddle.net/hfn5w1je/1/

// TODO step through instructions on key press
// TODO step through program on timer
// TODO highlight the next instruction and components (a, b, c, true, false)
// TODO highlight jumps
// TODO dynamically resize memory
// TODO compress memory representation via run-length encoding
// TODO add I/O capabilities (e.g. keyboard and terminal view)

window.onload = function() {
  stringToMem = function(s) {
      return s.split("")
          .map(function(v) {
              return v !== "0";
          });
  };

  overwrite = function(arr, i, s) {
    var j = 0;
    var sp = stringToMem(s);
    for (; j < sp.length; j += 1) {
      arr[i + j] = sp[j];
    }
  };

  bin = function(a) {
    v = a.toString(2);
    return (new Array(v.length + 1).join("1")) + "0" + v;
  };

  var n = 500;
  var arr = [];
  for (var i=0, t=n; i<t; i++) {
    // arr.push(Math.random() < 0.5 ? false : true);
      arr.push(false);
  }
  overwrite(arr, 0, [100, 100, 100, 0, 200].map(bin).join(""));
  overwrite(arr, 100, "0");
  overwrite(arr, 200, [100, 100, 100, 0, 200].map(bin).join(""));
  mem = arr;
  pointer = 0;
  pa = null;
  pb = null;
  pr = null;
  pt = null;
  pe = null;

  width = 1000;
  height = 1000;
  margin = 5;
  size = 20;
  columns = 30;
  bufferLeft = 10;
  bufferTop = 10;
  trueColor = "lightgray";
  falseColor = "darkslategray";
  pointerColor = "greenyellow";
  fill = {
    "true": {
      "true": "plum",
      "false": "lightgray"
    },
    "false": {
      "true": "slateblue",
      "false": "darkslategray"
    }
  }

  addressToColumn = function(a, columns) {
      return a % columns;
  }

  addressToRow = function(a) {
      return Math.floor(a / columns);
  }

  readNat = function(arr, i) {
    if (arr[i] == false) {
      return null;
    } else {
      var j = i;
      for (; arr[j]; j += 1) { }
      var a = arr.slice(j + 1, j + 1 + (j - i));
      var n = 0;
      a.map(function(v) { n *= 2; n += v ? 1 : 0; });
      return [n, j + 1 + (j - i)];
    }
  };

  readInst = function(arr, i) {
    var ra = readNat(arr, i);
    if (ra !== null) {
      pa = ra[0];
      var rb = readNat(arr, i + ra[1]);
      if (rb !== null) {
        pb = rb[0];
        var rr = readNat(arr, i + rb[1]);
        if (rr !== null) {
          pr = rr[0];
          var rt = readNat(arr, i + rr[1]);
          if (rt !== null) {
            pt = rt[0];
            var re = readNat(arr, i + rt[1]);
            if (re !== null) {
              pe = re[0];
            }
          }
        }
      }
    }
  }

  var stepButton = d3
    .select("body")
    .append("input")
    .attr("type", "button")
    .attr("value", "Step");

  svg = d3.select("body")
          .append("svg")
          .attr("width", width)
          .attr("height", height)
          .attr("display", "block");

  update = function() {
    readInst(mem, pointer);
    console.log(pa, pb, pr, pt, pe);
      stepButton.attr("disabled",
        (pa === null ||
        pb === null ||
        pr === null ||
        pt === null ||
        pe === null) ?
         true : null);

      svg
          .selectAll(".bit")
          .data(mem)
          .style("fill", function(v, i) { return fill[v][i == pointer]; });
  };

  svg
          .selectAll("rect")
          .data(mem)
          .enter()
          .append("rect")
          .attr("class", "bit")
          .attr("x", function(_, i) { return bufferLeft + (size + margin) * addressToColumn(i, columns); })
          .attr("y", function(_, i) { return bufferTop + (size + margin) * addressToRow(i); })
          .attr("width", size)
          .attr("height", size)
          .on("click", function(v, i) { mem[i] = !v; update(); });

    var step = function(a, b, c) {
      tf = !(arr[pa] || arr[pb]);
      mem[pr] = tf;
      pointer = tf ? pt : pe;
      console.log(arr[pa], arr[pb], tf);
      update();
    };

    stepButton.on("click", step);

    update();
};