caml_unix_random_seed: clarify fallback logic

Hopefully the new structure should make it easy to add new elements to
the random seed in the non-/dev/urandom case, in particular a domain
identifier for Multicore OCaml.

Changes

@@ -33,6 +33,9 @@ Working version
   64-bit floats in Cmm.memory_chunk.
   (Greta Yorsh, review by Xavier Leroy)
 
+- #????: refactor caml_sys_random_seed to ease future Multicore changes
+  (Gabriel Scherer, review by ???)
+
 - #10434: Pun labelled arguments with type constraint in function applications.
   (Greta Yorsh, review by Nicolas Chataing and Nicolás Ojeda Bär)
 

runtime/sys.c

@@ -566,6 +566,7 @@ int caml_unix_random_seed(intnat data[16])
 {
   int fd;
   int n = 0;
+
   /* Try /dev/urandom first */
   fd = open("/dev/urandom", O_RDONLY, 0);
   if (fd != -1) {
@@ -581,14 +582,14 @@ int caml_unix_random_seed(intnat data[16])
 #ifdef HAS_GETTIMEOFDAY
     struct timeval tv;
     gettimeofday(&tv, NULL);
-    data[n++] = tv.tv_usec;
-    data[n++] = tv.tv_sec;
+    if (n < 16) data[n++] = tv.tv_usec;
+    if (n < 16) data[n++] = tv.tv_sec;
 #else
-    data[n++] = time(NULL);
+    if (n < 16) data[n++] = time(NULL);
 #endif
 #ifdef HAS_UNISTD
-    data[n++] = getpid();
-    data[n++] = getppid();
+    if (n < 16) data[n++] = getpid();
+    if (n < 16) data[n++] = getppid();
 #endif
   }
   return n;