Introduce modular version.

src/util.c

@@ -0,0 +1,46 @@
+/*
+ * =======================================================================================
+ *
+ *      Author:   Jan Eitzinger (je), jan.eitzinger@fau.de
+ *      Copyright (c) 2020 RRZE, University Erlangen-Nuremberg
+ *
+ *      Permission is hereby granted, free of charge, to any person obtaining a copy
+ *      of this software and associated documentation files (the "Software"), to deal
+ *      in the Software without restriction, including without limitation the rights
+ *      to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *      copies of the Software, and to permit persons to whom the Software is
+ *      furnished to do so, subject to the following conditions:
+ *
+ *      The above copyright notice and this permission notice shall be included in all
+ *      copies or substantial portions of the Software.
+ *
+ *      THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *      IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *      FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *      AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *      LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *      OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *      SOFTWARE.
+ *
+ * =======================================================================================
+ */
+#include <util.h>
+
+/* Park/Miller RNG w/out MASKING, so as to be like f90s version */
+#define IA 16807
+#define IM 2147483647
+#define AM (1.0/IM)
+#define IQ 127773
+#define IR 2836
+#define MASK 123459876
+
+double myrandom(int* idum)
+{
+    int k= (*idum) / IQ;
+    double ans;
+
+    *idum = IA * (*idum - k * IQ) - IR * k;
+    if(*idum < 0) *idum += IM;
+    ans = AM * (*idum);
+    return ans;
+}