rand: add pcg32 and splitmix64 implementations

vlib/rand/pcg32_test.v

@@ -0,0 +1,27 @@
+
+import rand
+import time
+
+fn gen_randoms(initstate i64, initseq i64, bound int) []u32 {
+	mut randoms := [u32(0)].repeat(20)
+	mut rnd := rand.new_pcg32( u64(initstate), u64(initseq) )
+	for i in 0..20 {
+		randoms[i] = rnd.bounded_next(u32(bound))
+	}
+	return randoms
+}
+
+fn test_pcg32_reproducibility() {
+	t := time.ticks()
+	tseq := t % 23237671
+	println('t: $t | tseq: $tseq')
+	randoms1 := gen_randoms(t, tseq, 1000)
+	randoms2 := gen_randoms(t, tseq, 1000)
+	assert randoms1.len == randoms2.len
+	println( randoms1 )
+	println( randoms2 )
+	len := randoms1.len
+	for i in 0..len {
+		assert randoms1[i] == randoms2[i]
+	}	
+}