table.js

const TABLE_COUNT_OFFSET = 4,
      TABLE_HEAD_OFFSET = 12,
      TABLE_HEAD_SIZE = 16,
      TAG_OFFSET = 0,
      TAG_SIZE = 4,
      CHECKSUM_OFFSET = TAG_OFFSET + TAG_SIZE,
      CHECKSUM_SIZE = 4,
      CONTENTS_PTR_OFFSET = CHECKSUM_OFFSET + CHECKSUM_SIZE,
      CONTENTS_PTR_SIZE = 4,
      LENGTH_OFFSET = TABLE_HEAD_SIZE + CONTENTS_PTR_OFFSET;

exports.count = function(data) {
  return data.readUInt16BE(TABLE_COUNT_OFFSET);
};

exports.offset = function(data, name) {
  return exports.tableHead(data, name).contents;
};

exports.tableHead = function(data, name) {
  var numTables = exports.count(data);

  for (var i = 0; i < numTables; ++i) {
    var o = TABLE_HEAD_OFFSET + i * TABLE_HEAD_SIZE,
        tag = data.slice(o, o + CONTENTS_PTR_SIZE).toString();

    if (tag === name) {
      return {
        tag: tag,
        checksum: data.readUInt32BE(o + CHECKSUM_OFFSET),
        contents: data.readUInt32BE(o + CONTENTS_PTR_OFFSET),
        length: data.readUInt32BE(o + LENGTH_OFFSET)
      };
    }
  }
}