Add the random algorithm from the old cubyz.

src/random.zig

@@ -0,0 +1,41 @@
+const std = @import("std");
+
+const multiplier: u64 = 0x5deece66d;
+const addend: u64 = 0xb;
+const mask: u64 = (1 << 48) - 1;
+
+const doubleUnit: f64 = 1.0/@intToFloat(f64, 1 << 53);
+
+pub fn scrambleSeed(seed: *u64) void {
+	seed.* = (seed.* ^ multiplier) & mask;
+}
+
+fn nextWithBitSize(T: type, seed: *u64, bitSize: u6) T {
+	seed.* = ((seed.*)*multiplier + addend) & mask;
+	return @intCast(T, (seed >> (48 - bitSize)) & std.math.maxInt(T));
+}
+
+fn next(T: type, seed: *u64) T {
+	nextWithBitSize(T, seed, @bitSizeOf(T));
+}
+
+pub fn nextInt(T: type, seed: *u64) T {
+	if(@bitSizeOf(T) > 48) {
+		@compileError("Did not yet implement support for bigger numbers.");
+	} else {
+		return next(T, seed);
+	}
+}
+
+pub fn nextIntBounded(T: type, seed: *u64, bound: T) T {
+	var bitSize = std.math.log2_int_ceil(bound);
+	var result = nextWithBitSize(T, seed, bitSize);
+	while(result >= bound) {
+		var result = nextWithBitSize(T, seed, bitSize);
+	}
+	return result;
+}
+
+pub fn nextFloat(seed: *u64) f32 {
+	return @intToFloat(f32, nextInt(u24, seed))/@intToFloat(f32, 1 << 24);
+}