[flang] [llvm] [flang-rt] Runtime implementation of extended intrinsic function SECNDS() (PR #152021)

[Peter Klausler via llvm-commits]

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@@ -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}};
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klausler wrote:

maybe this should be `std::time_t`

https://github.com/llvm/llvm-project/pull/152021