minor.

lib/bcoin/chain.js

@@ -2531,5 +2531,37 @@ Chain.prototype.checkLocks = function checkLocks(tx, flags, entry, callback) {
   });
 };
 
+
+/**
+ * Calculate the difficulty.
+ * @param {ChainBlock} entry
+ * @returns {Number} Difficulty.
+ */
+
+Chain.prototype.getDifficulty = function getDifficulty(entry) {
+  var shift, diff;
+
+  if (!entry) {
+    if (!this.tip)
+      return 1.0;
+    entry = this.tip;
+  }
+
+  shift = (entry.bits >>> 24) & 0xff;
+  diff = 0x0000ffff / (entry.bits & 0x00ffffff);
+
+  while (shift < 29) {
+    diff *= 256.0;
+    shift++;
+  }
+
+  while (shift > 29) {
+    diff /= 256.0;
+    shift--;
+  }
+
+  return diff;
+};
+
 return Chain;
 };

lib/bcoin/protocol/constants.js

@@ -767,3 +767,11 @@ exports.confidence = {
 
   UNKNOWN: 0
 };
+
+/**
+ * The name of our currency.
+ * @const {String}
+ * @default
+ */
+
+exports.CURRENCY_UNIT = 'BTC';