[flang][runtime] Better non-repeatable RANDOM_INIT()

[klausler]

Use a higher-frequency clock base when initializing the pseudo-random number generator to implement
CALL RANDOM_INIT(REPEATABLE=.FALSE.)

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Changes

Use a higher-frequency clock base when initializing the pseudo-random number generator to implement
CALL RANDOM_INIT(REPEATABLE=.FALSE.)

---

Full diff: https://github.com/llvm/llvm-project/pull/67363.diff

1 Files Affected:

• (modified) flang/runtime/random.cpp (+4-2)

diff --git a/flang/runtime/random.cpp b/flang/runtime/random.cpp
index b7175d6b63c35f8..93113657bdecbca 100644
--- a/flang/runtime/random.cpp
+++ b/flang/runtime/random.cpp
@@ -20,10 +20,10 @@
 #include <algorithm>
 #include <cmath>
 #include <cstdint>
-#include <ctime>
 #include <limits>
 #include <memory>
 #include <random>
+#include <time.h>
 
 namespace Fortran::runtime {
 
@@ -100,7 +100,9 @@ void RTNAME(RandomInit)(bool repeatable, bool /*image_distinct*/) {
     if (repeatable) {
       generator.seed(0);
     } else {
-      generator.seed(std::time(nullptr));
+      timespec ts;
+      clock_gettime(CLOCK_REALTIME, &ts);
+      generator.seed(ts.tv_sec & ts.tv_nsec);
     }
   }
 }

[vdonaldson]

Ok, modulo the windows issue