code: function SigCache(size) {
    if (!(this instanceof SigCache))
      return new SigCache(size);
  
    if (size == null)
      size = 10000;
  
    assert(util.isU32(size));
  
    this.size = size;
    this.keys = [];
    this.valid = new Map();
  }
docs: Signature cache.
  @alias module:script.SigCache
  @constructor
  @param {Number} [size=10000]
  @property {Number} size
  @property {Hash[]} keys
  @property {Object} valid