Make the benchmarks print out stats

src/bench.h

@@ -0,0 +1,37 @@
+/**********************************************************************
+ * Copyright (c) 2014 Pieter Wuille                                   *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_BENCH_H_
+#define _SECP256K1_BENCH_H_
+
+#include <stdio.h>
+#include <math.h>
+#include "sys/time.h"
+
+static double gettimedouble(void) {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_usec * 0.000001 + tv.tv_sec;
+}
+
+void run_benchmark(void (*benchmark)(void*), void (*setup)(void*), void (*teardown)(void*), void* data, int count, int iter) {
+    double min = HUGE_VAL;
+    double sum = 0.0;
+    double max = 0.0;
+    for (int i = 0; i < count; i++) {
+        if (setup) setup(data);
+        double begin = gettimedouble();
+        benchmark(data);
+        double total = gettimedouble() - begin;
+        if (teardown) teardown(data);
+        if (total < min) min = total;
+        if (total > max) max = total;
+        sum += total;
+    }
+    printf("min %.3fus / avg %.3fus / max %.3fus\n", min * 1000000.0 / iter, (sum / count) * 1000000.0 / iter, max * 1000000.0 / iter);
+}
+
+#endif