[flang-commits] [flang] 301a0db - [flang][runtime] Better non-repeatable RANDOM_INIT() (#67363)

[via flang-commits]

Author: Peter Klausler
Date: 2023-10-16T14:29:40-07:00
New Revision: 301a0dba56e176e3f236fc069405e3b929a76c94

URL: https://github.com/llvm/llvm-project/commit/301a0dba56e176e3f236fc069405e3b929a76c94
DIFF: https://github.com/llvm/llvm-project/commit/301a0dba56e176e3f236fc069405e3b929a76c94.diff

LOG: [flang][runtime] Better non-repeatable RANDOM_INIT() (#67363)

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

Added: 
    

Modified: 
    flang/runtime/random.cpp

Removed: 
    


################################################################################
diff  --git a/flang/runtime/random.cpp b/flang/runtime/random.cpp
index b7175d6b63c35f8..8b00cfd1cac1950 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 +100,13 @@ void RTNAME(RandomInit)(bool repeatable, bool /*image_distinct*/) {
     if (repeatable) {
       generator.seed(0);
     } else {
-      generator.seed(std::time(nullptr));
+#ifdef CLOCK_REALTIME
+      timespec ts;
+      clock_gettime(CLOCK_REALTIME, &ts);
+      generator.seed(ts.tv_sec & ts.tv_nsec);
+#else
+      generator.seed(time(nullptr));
+#endif
     }
   }
 }