[test] Avoid seeding random number generators with time. NFC (#23050)

Using the current time to seed the random number generator in tests will
make them non-determinisitic. Simply using the default seed or seeding
with a fixed value seem fine all of these test cases.

Author: sbc100

test/benchmark/benchmark_utf16.cpp

@@ -54,7 +54,6 @@ unsigned short *randomString(int len) {
 }
 
 int main() {
-  srand(time(NULL));
   double t = 0;
   double t2 = emscripten_get_now();
   for(int i = 0; i < 10; ++i) {

test/benchmark/benchmark_utf8.c

@@ -54,9 +54,6 @@ char *randomString(int len) {
 }
 
 int main() {
-  time_t seed = time(NULL);
-  printf("Random seed: %lld\n", seed);
-  srand(seed);
   double t = 0;
   double t2 = emscripten_get_now();
   for (int i = 0; i < 100000; ++i) {

test/code_size/random_printf_wasm.json

@@ -1,6 +1,6 @@
 {
-  "a.html": 12686,
-  "a.html.gz": 6930,
-  "total": 12686,
-  "total_gz": 6930
+  "a.html": 12597,
+  "a.html.gz": 6882,
+  "total": 12597,
+  "total_gz": 6882
 }

test/code_size/random_printf_wasm2js.json

@@ -1,6 +1,6 @@
 {
-  "a.html": 17266,
-  "a.html.gz": 7515,
-  "total": 17266,
-  "total_gz": 7515
+  "a.html": 17195,
+  "a.html.gz": 7478,
+  "total": 17195,
+  "total_gz": 7478
 }

test/core/test_emmalloc.c

@@ -178,7 +178,6 @@ void randoms() {
   for (int i = 0; i < BINS; i++) {
     bins[i] = NULL;
   }
-  srandom(1337101);
   for (int i = 0; i < RANDOM_ITERS; i++) {
     unsigned int r = random();
     int alloc = r & 1;

test/core/test_rand.c

@@ -0,0 +1,42 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <assert.h>
+
+int main() {
+  // We need RAND_MAX to be a bitmask (power of 2 minus 1).  This assertion will
+  // error if RAND_MAX ever changes, so we don't miss that.
+  assert(RAND_MAX == 0x7fffffff);
+
+  srand(0xdeadbeef);
+  for (int i = 0; i < 10; ++i) {
+    printf("%d\n", rand());
+  }
+
+  unsigned int seed = 0xdeadbeef;
+  for (int i = 0; i < 10; ++i) {
+    printf("%d\n", rand_r(&seed));
+  }
+
+  bool haveEvenAndOdd = true;
+  for (int i = 1; i <= 30; ++i) {
+    int mask = 1 << i;
+    if (mask > RAND_MAX) break;
+    bool haveEven = false;
+    bool haveOdd = false;
+    for (int j = 0; j < 1000 && (!haveEven || !haveOdd); ++j) {
+      if ((rand() & mask) == 0) {
+        haveEven = true;
+      } else {
+        haveOdd = true;
+      }
+    }
+    haveEvenAndOdd = haveEvenAndOdd && haveEven && haveOdd;
+  }
+
+  if (haveEvenAndOdd) {
+    printf("Have even and odd!\n");
+  }
+
+  return 0;
+}

test/core/test_rand.out

@@ -0,0 +1,21 @@
+490242850
+2074599277
+1480056542
+1912638067
+931112055
+2110392489
+2053422194
+1614832492
+216117595
+174823244
+760368382
+602359081
+1121118963
+1291018924
+1608306807
+352705809
+958258461
+1182561381
+114276303
+1481323674
+Have even and odd!

test/fetch/test_fetch_idb_store.c

@@ -38,7 +38,6 @@ int main()
 {
   // Create data
   uint8_t *data = (uint8_t*)malloc(10240);
-  srand(time(NULL));
   for(int i = 0; i < 10240; ++i) data[i] = (uint8_t)rand();
 
   persistFileToIndexedDB("outputfile.dat", data, 10240);

test/fetch/test_fetch_idb_store.cpp

@@ -21,7 +21,6 @@ int main()
   strcpy(attr.requestMethod, "EM_IDB_STORE");
   attr.attributes = EMSCRIPTEN_FETCH_REPLACE | EMSCRIPTEN_FETCH_SYNCHRONOUS | EMSCRIPTEN_FETCH_PERSIST_FILE;
   uint8_t *data = (uint8_t*)malloc(TEST_SIZE);
-  srand(time(NULL));
   for(int i = 0; i < TEST_SIZE; ++i)
     data[i] = (uint8_t)rand() | 0x40;
   attr.requestData = (char *)data;

test/hello_random_printf.c

@@ -4,7 +4,7 @@
 #include <emscripten.h>
 
 int main() {
-  srand(time(NULL));
+  srand(0);
 
   printf("hello: a random string: %s, an integer: %d, a float: %f. Time now: %f\n",
     emscripten_random() > 0.5 ? "test" : "test2",