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-rw-r--r--libc/stdlib/rand.c61
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