chain: use binary search for byTime.

lib/bcoin/chain.js

@@ -437,25 +437,32 @@ Chain.prototype.byHash = function byHash(hash) {
 };
 
 Chain.prototype.byTime = function byTime(ts) {
-  var i, delta, existing;
-  var step = 1;
+  var start = 0;
+  var end = this.index.count;
+  var pos, delta, entry;
 
   if (ts >= this.tip.ts)
     return this.tip;
 
-  for (i = this.index.count - 1; i >= 0; i -= step) {
-    existing = this.db.get(i);
+  // Do a binary search for a block
+  // mined within an hour of the
+  // timestamp.
+  while (start < end) {
+    pos = (start + end) >> 1;
+    entry = this.db.get(pos);
+    delta = Math.abs(ts - entry.ts);
 
-    if (ts >= existing.ts)
-      return existing;
+    if (delta <= 60 * 60)
+      return entry;
 
-    delta = existing.ts - ts;
-    // If they're more than 1000 blocks apart
-    if (delta > 1000 * 60 * 10)
-      step *= 2;
+    if (ts < entry.ts) {
+      end = pos;
+    } else {
+      start = pos + 1;
+    }
   }
 
-  return this.db.get(0);
+  return this.db.get(start);
 };
 
 Chain.prototype.hasBlock = function hasBlock(hash) {