add a simple C benchmark example

.gitignore

@@ -1,3 +1,4 @@
 *
 !*/
 !*.*
+a.out

examples/bench_perm.c

@@ -0,0 +1,74 @@
+
+// $ gcc -O2 bench_perm.c ../cbits/goldilocks.c
+
+#include <stdint.h>
+
+#include "../cbits/goldilocks.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+//------------------------------------------------------------------------------
+
+int64_t get_usec() {
+  int64_t start;
+  struct timeval timecheck;
+  gettimeofday(&timecheck, NULL);
+  start = (int64_t)timecheck.tv_sec * 1000000 + (int64_t)timecheck.tv_usec;
+  return start;
+}
+
+void print_elapsed_time(const char *msg, int64_t start, int64_t stop) {
+  printf("%s took %lld usecs\n" ,msg, stop-start );
+}
+
+//------------------------------------------------------------------------------
+
+void benchmark_poseidon2_perm(int N) {  
+  printf("\nbenchmarking iterated Poseidon2 permutations with N = %d\n",N);
+
+  uint64_t state[12];
+  for(int i=0; i<12; i++) state[i] = i;
+
+  int64_t start = get_usec();
+  for(int i=0; i<N; i++) { 
+    goldilocks_poseidon2_permutation(state);
+  }
+  int64_t stop = get_usec();
+  print_elapsed_time( "N iterated Poseidon2 permutations" , start, stop );
+}
+
+
+void benchmark_monolith_perm(int N) {
+  printf("\nbenchmarking iterated Monolith permutations with N = %d\n",N);
+
+  uint64_t state[12];
+  for(int i=0; i<12; i++) state[i] = i;
+
+  int64_t start = get_usec();
+  for(int i=0; i<N; i++) { 
+    goldilocks_monolith_permutation(state);
+  }
+  int64_t stop = get_usec();
+  print_elapsed_time( "N iterated Monolith permutations" , start, stop );
+}
+ 
+
+//------------------------------------------------------------------------------
+
+int main(int argc, char *argv[]) {
+  int N = 1000000;
+
+  if (argc >= 2) {
+    N = atoi(argv[1]);
+  }
+
+  benchmark_poseidon2_perm(N);
+  benchmark_monolith_perm (N);
+
+  return 0;
+}