1 files changed, 61 insertions, 0 deletions
diff --git a/libc/stdlib/rand.c b/libc/stdlib/rand.c
new file mode 100644
index 000000000..4eb07894b
--- /dev/null
+++ b/libc/stdlib/rand.c
@@ -0,0 +1,61 @@
+#ifdef ZX81_RNG
+/*
+ * This is my favorite tiny RNG, If you had a ZX81 you may recognise it :-)
+ *								(RdeBath)
+ */
+
+#include <stdlib.h>
+
+#define MAXINT (((unsigned)-1)>>1)
+
+static unsigned int sseed = 0;
+
+int rand()
+{
+   return ( sseed = (((sseed+1L)*75L)%65537L)-1 ) & MAXINT;
+}
+
+void srand(seed)
+unsigned int seed;
+{
+   sseed=seed;
+}
+
+#else
+
+/*
+ * This generator is a combination of three linear congruential generators
+ * with periods or 2^15-405, 2^15-1041 and 2^15-1111. It has a period that
+ * is the product of these three numbers.
+ */
+
+static int seed1 = 1;
+static int seed2 = 1;
+static int seed3 = 1;
+#define MAXINT (((unsigned)-1)>>1)
+
+#define CRANK(a,b,c,m,s) 	\
+	q = s/a;		\
+	s = b*(s-a*q) - c*q;	\
+	if(s<0) s+=m;
+
+int rand()
+{
+   register int q, z;
+   CRANK(206, 157,  31, 32363, seed1);
+   CRANK(217, 146,  45, 31727, seed2);
+   CRANK(222, 142, 133, 31657, seed3);
+
+   return seed1^seed2^seed3;
+}
+
+void srand(seed)
+unsigned int seed;
+{
+   seed &= MAXINT;
+   seed1= seed%32362 + 1;
+   seed2= seed%31726 + 1;
+   seed3= seed%31656 + 1;
+}
+
+#endif