[flang-rt] Runtime implementation of extended intrinsic function SECNDS()

flang-rt/lib/runtime/command.cpp

@@ -12,6 +12,7 @@
 #include "flang-rt/runtime/stat.h"
 #include "flang-rt/runtime/terminator.h"
 #include "flang-rt/runtime/tools.h"
+#include "flang/Runtime/extensions.h"
 #include <cerrno>
 #include <cstdlib>
 #include <limits>
@@ -309,6 +310,12 @@ std::int32_t RTNAME(Hostnm)(
   return status;
 }
 
+float RTNAME(Secnds)(float *refTime, const char *sourceFile, int line) {
+  Terminator terminator{sourceFile, line};
+  RUNTIME_CHECK(terminator, refTime != nullptr);
+  return FORTRAN_PROCEDURE_NAME(secnds)(refTime);
+}
+
 std::int32_t RTNAME(PutEnv)(
     const char *str, size_t str_length, const char *sourceFile, int line) {
   Terminator terminator{sourceFile, line};

flang-rt/lib/runtime/extensions.cpp

@@ -303,6 +303,47 @@ void FORTRAN_PROCEDURE_NAME(qsort)(int *array, int *len, int *isize,
 // PERROR(STRING)
 void RTNAME(Perror)(const char *str) { perror(str); }
 
+// GNU extension function SECNDS(refTime)
+float FORTRAN_PROCEDURE_NAME(secnds)(float *refTime) {
+  constexpr float FAIL_SECNDS{-1.0f}; // Failure code for this function
+  // Failure code for time functions that return std::time_t
+  constexpr time_t FAIL_TIME{std::time_t{-1}};
+  if (!refTime) {
+    return FAIL_SECNDS;
+  }
+  std::time_t now{std::time(nullptr)};
+  if (now == FAIL_TIME) {
+    return FAIL_SECNDS;
+  }
+  // In float result, we can only precisely store 2^24 seconds, which
+  // comes out to about 194 days. Thus, need to pick a starting point.
+  // Given the description of this function, midnight of the current
+  // day is the best starting point.
+  static time_t startingPoint{0};
+  if (!startingPoint) {
+    struct tm timeInfo;
+#ifdef _WIN32
+    if (localtime_s(&timeInfo, &now)) {
+      return FAIL_SECNDS;
+    }
+#else
+    if (!localtime_r(&now, &timeInfo)) {
+      return FAIL_SECNDS;
+    }
+#endif
+    // Back to midnight
+    timeInfo.tm_hour = 0;
+    timeInfo.tm_min = 0;
+    timeInfo.tm_sec = 0;
+    startingPoint = std::mktime(&timeInfo);
+    if (startingPoint == FAIL_TIME) {
+      return FAIL_SECNDS;
+    }
+  }
+  double diffStartingPoint{std::difftime(now, startingPoint)};
+  return static_cast<float>(diffStartingPoint) - *refTime;
+}
+
 // GNU extension function TIME()
 std::int64_t RTNAME(time)() { return time(nullptr); }
 

flang/include/flang/Runtime/command.h

@@ -67,6 +67,8 @@ std::int32_t RTNAME(Hostnm)(
 std::int32_t RTNAME(PutEnv)(
     const char *str, size_t str_length, const char *sourceFile, int line);
 
+float RTNAME(Secnds)(float *refTime, const char *sourceFile, int line);
+
 // Calls unlink()
 std::int32_t RTNAME(Unlink)(
     const char *path, size_t pathLength, const char *sourceFile, int line);

flang/include/flang/Runtime/extensions.h

@@ -90,5 +90,8 @@ void RTNAME(Perror)(const char *str);
 // MCLOCK -- returns accumulated time in ticks
 int FORTRAN_PROCEDURE_NAME(mclock)();
 
+// GNU extension subroutine SECNDS(refTime)
+float FORTRAN_PROCEDURE_NAME(secnds)(float *refTime);
+
 } // extern "C"
 #endif // FORTRAN_RUNTIME_EXTENSIONS_H_