runtime: add fastrand

This is needed for hash/maphash support.

Author: aykevl

src/runtime/algorithm.go

@@ -0,0 +1,22 @@
+package runtime
+
+// This file implements various core algorithms used in the runtime package and
+// standard library.
+
+// This function is used by hash/maphash.
+func fastrand() uint32 {
+	xorshift32State = xorshift32(xorshift32State)
+	return xorshift32State
+}
+
+var xorshift32State uint32 = 1
+
+func xorshift32(x uint32) uint32 {
+	// Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs".
+	// Improved sequence based on
+	// http://www.iro.umontreal.ca/~lecuyer/myftp/papers/xorshift.pdf
+	x ^= x << 7
+	x ^= x >> 1
+	x ^= x << 9
+	return x
+}