rand: reorganize: phase 2

vlib/rand/util/util.v

@@ -0,0 +1,50 @@
+// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+module util
+
+import time
+
+// Commonly used constants across RNGs
+pub const (
+	lower_mask     = u64(0x00000000FFFFFFFF)
+	max_u32        = 0xFFFFFFFF
+	max_u64        = 0xFFFFFFFFFFFFFFFF
+	max_u32_as_f32 = f32(max_u32) + 1
+	max_u64_as_f64 = f64(max_u64) + 1
+	u31_mask       = u32(0x7FFFFFFF)
+	u63_mask       = u64(0x7FFFFFFFFFFFFFFF)
+)
+
+// Constants taken from Numerical Recipes
+[inline]
+fn nr_next(prev u32) u32 {
+	return prev * 1664525 + 1013904223
+}
+
+// time_seed_array is a utility function that returns the required number of u32s generated from system time
+[inline]
+pub fn time_seed_array(count int) []u32 {
+	mut seed := u32(time.now().unix_time())
+	mut seed_data := []u32{cap: count}
+	for _ in 0 .. count {
+		seed = nr_next(seed)
+		seed_data << nr_next(seed)
+	}
+	return seed_data
+}
+
+// time_seed_32 returns a 32-bit seed geenrated from system time
+[inline]
+pub fn time_seed_32() u32 {
+	return time_seed_array(1)[0]
+}
+
+// time_seed_64 returns a 64-bit seed geenrated from system time
+[inline]
+pub fn time_seed_64() u64 {
+	seed_data := time_seed_array(2)
+	lower := u64(seed_data[0])
+	upper := u64(seed_data[1])
+	return lower | (upper << 32)
+}