1 files changed, 88 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/rg_rand.c b/reference/C/CONTRIB/SNIP/rg_rand.c
new file mode 100755
index 0000000..578f70a
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+++ b/reference/C/CONTRIB/SNIP/rg_rand.c
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+/*
+**  longrand() -- generate 2**31-2 random numbers
+**
+**  public domain by Ray Gardner
+** 
+**  based on "Random Number Generators: Good Ones Are Hard to Find",
+**  S.K. Park and K.W. Miller, Communications of the ACM 31:10 (Oct 1988),
+**  and "Two Fast Implementations of the 'Minimal Standard' Random
+**  Number Generator", David G. Carta, Comm. ACM 33, 1 (Jan 1990), p. 87-88
+**
+**  linear congruential generator f(z) = 16807 z mod (2 ** 31 - 1)
+**
+**  uses L. Schrage's method to avoid overflow problems
+*/
+
+#define a 16807         /* multiplier */
+#define m 2147483647L   /* 2**31 - 1 */
+#define q 127773L       /* m div a */
+#define r 2836          /* m mod a */
+
+long nextlongrand(long seed)
+{
+      unsigned long lo, hi;
+
+      lo = a * (long)(seed & 0xFFFF);
+      hi = a * (long)((unsigned long)seed >> 16);
+      lo += (hi & 0x7FFF) << 16;
+      if (lo > m)
+      {
+            lo &= m;
+            ++lo;
+      }
+      lo += hi >> 15;
+      if (lo > m)
+      {
+            lo &= m;
+            ++lo;
+      }
+      return (long)lo;
+}
+
+static long randomnum = 1;
+
+long longrand(void)                     /* return next random long */
+{
+      randomnum = nextlongrand(randomnum);
+      return randomnum;
+}
+
+void slongrand(unsigned long seed)      /* to seed it */
+{
+      randomnum = seed ? (seed & m) : 1;  /* nonzero seed */
+}
+
+
+#ifdef TEST
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+      long reps, k, num;
+      unsigned long seed;
+
+      reps = 10000;
+      seed = 1;
+
+      /*
+      ** correctness test: after 10000 reps starting with seed 1,
+      ** result should be 1043618065
+      */
+    
+      if (argc > 1)
+            reps = atol(argv[1]);
+      if (argc > 2)
+            seed = atol(argv[2]);
+
+      printf("seed %ld for %ld reps...\n", seed, reps);
+      slongrand(seed);
+      for (k = 0; k < reps; ++k)
+            num = longrand();
+      printf("%ld\n", num);
+
+      return 0;
+}
+
+#endif