tests: add "help" command line flag and output

Makefile.am

@@ -49,6 +49,7 @@ noinst_HEADERS += src/precomputed_ecmult_gen.h
 noinst_HEADERS += src/assumptions.h
 noinst_HEADERS += src/checkmem.h
 noinst_HEADERS += src/util.h
+noinst_HEADERS += src/cli_util.h
 noinst_HEADERS += src/int128.h
 noinst_HEADERS += src/int128_impl.h
 noinst_HEADERS += src/int128_native.h

src/bench.c

@@ -9,6 +9,7 @@
 
 #include "../include/secp256k1.h"
 #include "util.h"
+#include "cli_util.h"
 #include "bench.h"
 
 static void help(int default_iters) {

src/bench.h

@@ -129,18 +129,6 @@ static void run_benchmark(char *name, void (*benchmark)(void*, int), void (*setu
     printf("\n");
 }
 
-static int have_flag(int argc, char** argv, char *flag) {
-    char** argm = argv + argc;
-    argv++;
-    while (argv != argm) {
-        if (strcmp(*argv, flag) == 0) {
-            return 1;
-        }
-        argv++;
-    }
-    return 0;
-}
-
 /* takes an array containing the arguments that the user is allowed to enter on the command-line
    returns:
       - 1 if the user entered an invalid argument

src/bench_ecmult.c

@@ -9,6 +9,7 @@
 #include "../include/secp256k1.h"
 
 #include "util.h"
+#include "cli_util.h"
 #include "hash_impl.h"
 #include "field_impl.h"
 #include "group_impl.h"

src/bench_internal.c

@@ -10,6 +10,7 @@
 
 #include "assumptions.h"
 #include "util.h"
+#include "cli_util.h"
 #include "hash_impl.h"
 #include "field_impl.h"
 #include "group_impl.h"

src/cli_util.h

@@ -0,0 +1,24 @@
+/***********************************************************************
+ * Copyright (c) 2023 Jonas Nick                                       *
+ * Distributed under the MIT software license, see the accompanying    *
+ * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
+ ***********************************************************************/
+
+#ifndef SECP256K1_CLI_UTIL_H
+#define SECP256K1_CLI_UTIL_H
+
+#include <string.h>
+
+static int have_flag(int argc, char** argv, char *flag) {
+    char** argm = argv + argc;
+    argv++;
+    while (argv != argm) {
+        if (strcmp(*argv, flag) == 0) {
+            return 1;
+        }
+        argv++;
+    }
+    return 0;
+}
+
+#endif /* SECP256K1_CLI_UTIL_H */

src/tests.c

@@ -16,6 +16,7 @@
 #include "testrand_impl.h"
 #include "checkmem.h"
 #include "util.h"
+#include "cli_util.h"
 
 #include "../contrib/lax_der_parsing.c"
 #include "../contrib/lax_der_privatekey_parsing.c"
@@ -28,7 +29,8 @@
 
 #define CONDITIONAL_TEST(cnt, nam) if (COUNT < (cnt)) { printf("Skipping %s (iteration count too low)\n", nam); } else
 
-static int COUNT = 64;
+static const int DEFAULT_COUNT = 64;
+static int COUNT = DEFAULT_COUNT;
 static secp256k1_context *CTX = NULL;
 static secp256k1_context *STATIC_CTX = NULL;
 
@@ -7428,6 +7430,21 @@ static void run_cmov_tests(void) {
     ge_storage_cmov_test();
 }
 
+static void help(void) {
+    printf("The command ./tests runs a test suite on the code base.\n");
+    printf("\n");
+    printf("Some randomized tests are run for a certain number of iterations,\n");
+    printf("which is set to %d by default. This number can be altered by either\n", DEFAULT_COUNT);
+    printf("setting the environment variable SECP256K1_TEST_ITERS or by providing\n");
+    printf("the iteration count as a command line argument.\n");
+    printf("\n");
+    printf("Usage: ./tests [args]\n");
+    printf("Available arguments:\n");
+    printf("    help              : display this help message and exit\n");
+    printf("    <count>           : set the iteration count to <count>\n");
+    printf("\n");
+}
+
 int main(int argc, char **argv) {
     /* Disable buffering for stdout to improve reliability of getting
      * diagnostic information. Happens right at the start of main because
@@ -7437,6 +7454,15 @@ int main(int argc, char **argv) {
      * unbuffered on all systems. */
     setbuf(stderr, NULL);
 
+    if (argc > 1) {
+        if (have_flag(argc, argv, "-h")
+           || have_flag(argc, argv, "--help")
+           || have_flag(argc, argv, "help")) {
+            help();
+            return 0;
+        }
+    }
+
     /* find iteration count */
     if (argc > 1) {
         COUNT = strtol(argv[1], NULL, 0);