bench: compare binaries equal times

The benchmark compare would drop the last run of the binary pairs. So
when they were only run once an error would arise because no data was
generated for the second binary.

benchmark/compare.js

@@ -48,36 +48,24 @@ if (nodes.length !== 2)
 
 var spawn = require('child_process').spawn;
 var results = {};
-var n = 1;
+var toggle = 1;
+var r = (+process.env.NODE_BENCH_RUNS || 1) * 2;
 
 run();
-
-var RUNS = +process.env.NODE_BENCH_RUNS || 1;
-var r = RUNS;
 function run() {
-  // Flip back and forth between the two binaries.
-  if (n === 1) {
-    n--;
-  } else {
-    r--;
-    if (r === 0)
-      return compare();
-    else
-      n++;
-  }
-
-  if (n === -1)
+  if (--r < 0)
     return compare();
+  toggle = ++toggle % 2;
 
-  var node = nodes[n];
+  var node = nodes[toggle];
   console.error('running %s', node);
   var env = {};
   for (var i in process.env)
     env[i] = process.env[i];
   env.NODE = node;
-  var child = spawn('make', [runBench], { env: env });
 
   var out = '';
+  var child = spawn('make', [runBench], { env: env });
   child.stdout.setEncoding('utf8');
   child.stdout.on('data', function(c) {
     out += c;