Format benchmark command line output

1. add function `print_output_table_header_row` to src/bench.h to print the table header
2. modify the following benchmarks to include the table header
    - bench_ecdh.c
    - bench_ecmult.c
    - bench_internal.c
    - bench_recover.c
    - bench_schnorrsig.c
    - bench_sign.c
    - bench_verify.c

src/bench.h

@@ -70,7 +70,7 @@ void print_number(const int64_t x) {
     if (x < 0) {
         buffer[--ptr] = '-';
     }
-    printf("%s", &buffer[ptr]);
+    printf("%-15s", &buffer[ptr]);
 }
 
 void run_benchmark(char *name, void (*benchmark)(void*, int), void (*setup)(void*), void (*teardown)(void*, int), void* data, int count, int iter) {
@@ -97,13 +97,11 @@ void run_benchmark(char *name, void (*benchmark)(void*, int), void (*setup)(void
         }
         sum += total;
     }
-    printf("%s: min ", name);
+    printf("%-30s ", name);
     print_number(min * FP_MULT / iter);
-    printf("us / avg ");
     print_number(((sum * FP_MULT) / count) / iter);
-    printf("us / max ");
     print_number(max * FP_MULT / iter);
-    printf("us\n");
+    printf("\n");
 }
 
 int have_flag(int argc, char** argv, char *flag) {
@@ -130,4 +128,11 @@ int get_iters(int default_iters) {
     }
 }
 
+void print_output_table_header_row(void) {
+    int i;
+    printf("%-30s %-15s %-15s %-15s\n", "Benchmark", "Min(μs)", "Avg(μs)", "Max(μs)");
+    for(i=0; i<70; i++) printf("-");
+    printf("\n");
+}
+
 #endif /* SECP256K1_BENCH_H */

src/bench_ecdh.c

@@ -52,6 +52,8 @@ int main(void) {
     /* create a context with no capabilities */
     data.ctx = secp256k1_context_create(SECP256K1_FLAGS_TYPE_CONTEXT);
 
+    print_output_table_header_row();
+
     run_benchmark("ecdh", bench_ecdh, bench_ecdh_setup, NULL, &data, 10, iters);
 
     secp256k1_context_destroy(data.ctx);

src/bench_ecmult.c

@@ -333,6 +333,7 @@ int main(int argc, char **argv) {
     secp256k1_ge_set_all_gej_var(data.pubkeys, data.pubkeys_gej, POINTS);
 
 
+    print_output_table_header_row();
     /* Initialize offset1 and offset2 */
     hash_into_offset(&data, 0);
     run_ecmult_bench(&data, iters);

src/bench_internal.c

@@ -344,6 +344,7 @@ void bench_context_sign(void* arg, int iters) {
 int main(int argc, char **argv) {
     bench_inv data;
     int iters = get_iters(20000);
+    print_output_table_header_row();
 
     if (have_flag(argc, argv, "scalar") || have_flag(argc, argv, "add")) run_benchmark("scalar_add", bench_scalar_add, bench_setup, NULL, &data, 10, iters*100);
     if (have_flag(argc, argv, "scalar") || have_flag(argc, argv, "negate")) run_benchmark("scalar_negate", bench_scalar_negate, bench_setup, NULL, &data, 10, iters*100);

src/bench_recover.c

@@ -55,6 +55,8 @@ int main(void) {
 
     data.ctx = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
 
+    print_output_table_header_row();
+
     run_benchmark("ecdsa_recover", bench_recover, bench_recover_setup, NULL, &data, 10, iters);
 
     secp256k1_context_destroy(data.ctx);

src/bench_schnorrsig.c

@@ -86,6 +86,7 @@ int main(void) {
         CHECK(secp256k1_xonly_pubkey_serialize(data.ctx, pk_char, &pk) == 1);
     }
 
+    print_output_table_header_row();
     run_benchmark("schnorrsig_sign", bench_schnorrsig_sign, NULL, NULL, (void *) &data, 10, iters);
     run_benchmark("schnorrsig_verify", bench_schnorrsig_verify, NULL, NULL, (void *) &data, 10, iters);
 

src/bench_sign.c

@@ -51,6 +51,8 @@ int main(void) {
 
     data.ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
 
+    print_output_table_header_row();
+
     run_benchmark("ecdsa_sign", bench_sign_run, bench_sign_setup, NULL, &data, 10, iters);
 
     secp256k1_context_destroy(data.ctx);

src/bench_verify.c

@@ -103,6 +103,7 @@ int main(void) {
     data.pubkeylen = 33;
     CHECK(secp256k1_ec_pubkey_serialize(data.ctx, data.pubkey, &data.pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED) == 1);
 
+    print_output_table_header_row();
     run_benchmark("ecdsa_verify", bench_verify, NULL, NULL, &data, 10, iters);
 #ifdef ENABLE_OPENSSL_TESTS
     data.ec_group = EC_GROUP_new_by_curve_name(NID_secp256k1);