[flang] [llvm] [flang/flang-rt] Adding support of RAND, IRAND and SRAND intrinsics (PR #166780)

[Kelvin Li via llvm-commits]

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@@ -398,6 +406,55 @@ std::int64_t RTNAME(time)() { return time(nullptr); }
 // MCLOCK: returns accumulated CPU time in ticks
 std::int32_t FORTRAN_PROCEDURE_NAME(mclock)() { return std::clock(); }
 
+static void _internal_srand(int seed) { rand_seed = seed ? seed : 123459876; }
+
+// IRAND(I)
+int RTNAME(Irand)(int *i) {
+  int j;
+  if (i)
+    j = *i;
+  else
+    j = 0;
+
+  rand_seed_lock.Take();
+  switch (j) {
+  case 0:
+    break;
+  case 1:
+    _internal_srand(0);
+    break;
+  default:
+    _internal_srand(j);
+    break;
+  }
+
+  rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
+  j = (int)rand_seed;
+  rand_seed_lock.Drop();
+  return j;
+}
+
+// RAND(I)
+float RTNAME(Rand)(int *i) {
+  unsigned mask = 0;
+  auto radix = std::numeric_limits<float>::radix;
+  auto digits = std::numeric_limits<float>::digits;
+  if (radix == 2)
+    mask = ~(unsigned)0u << (32 - digits + 1);
+  else if (radix == 16)
+    mask = ~(unsigned)0u << ((8 - digits) * 4 + 1);
+  else
+    std::fprintf(stderr, "Radix unknown value");
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kkwli wrote:

I am not sure if it is the way to handle error/warning message here. Need others to chime in.

https://github.com/llvm/llvm-project/pull/166780