Biased random generator

gen/rand.go

@@ -0,0 +1,10 @@
+package gen
+
+import "math/rand"
+
+// Generate a random uint64 with an even distribution of bits.Len64()
+func RandBiasedUint64() uint64 {
+	// The shift-right by up to 64 (shifting it to 0) makes up for randomness
+        // lost by setting the high bit.
+	return (rand.Uint64() | 0x8000000000000000) >> rand.Int31n(65)
+}