From c877ddd21f402381d88a6bebdd5c7c0b4ac28ba9 Mon Sep 17 00:00:00 2001
From: Daniel Karbach <daniel.karbach@localhorst.tv>
Date: Mon, 23 Mar 2015 17:33:02 +0100
Subject: [PATCH] added Galois LFSR PRNG

not in use yet
beware of seed with many zeros
especially 0, which will only ever produce zeroes
---
 TODO          |  6 ++++++
 src/noise.cpp | 18 ++++++++++++++++++
 src/noise.hpp | 29 +++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/TODO b/TODO
index dfe8332..244e938 100644
--- a/TODO
+++ b/TODO
@@ -75,3 +75,9 @@ world generator that is not boring
 entity/world collision
 
 	entities should be stopped from entering solid parts of the world
+
+better noise
+
+	current simplex noise implementation repeats itself pretty quickly
+	also there seems to be a (imo) better implementation here:
+	http://flafla2.github.io/2014/08/09/perlinnoise.html
diff --git a/src/noise.cpp b/src/noise.cpp
index c86f833..6d59224 100644
--- a/src/noise.cpp
+++ b/src/noise.cpp
@@ -12,6 +12,24 @@ constexpr float one_sixth = 1.0f/6.0f;
 
 namespace blank {
 
+GaloisLFSR::GaloisLFSR(std::uint64_t seed)
+: state(seed) {
+
+}
+
+bool GaloisLFSR::operator ()() {
+	bool result = state & 1;
+	state >>= 1;
+	if (result) {
+		state |= 0x8000000000000000;
+		state ^= mask;
+	} else {
+		state &= 0x7FFFFFFFFFFFFFFF;
+	}
+	return result;
+}
+
+
 SimplexNoise::SimplexNoise(unsigned int seed)
 : grad({
 	{  1.0f,  1.0f,  0.0f },
diff --git a/src/noise.hpp b/src/noise.hpp
index 4c26de9..166a60a 100644
--- a/src/noise.hpp
+++ b/src/noise.hpp
@@ -1,11 +1,40 @@
 #ifndef BLANK_NOISE_HPP_
 #define BLANK_NOISE_HPP_
 
+#include <cstdint>
+#include <limits>
 #include <glm/glm.hpp>
 
 
 namespace blank {
 
+class GaloisLFSR {
+
+public:
+	// seed should be non-zero
+	explicit GaloisLFSR(std::uint64_t seed);
+
+	// get the next bit
+	bool operator ()();
+
+	template<class T>
+	void operator ()(T &out) {
+		constexpr int num_bits =
+			std::numeric_limits<T>::digits +
+			std::numeric_limits<T>::is_signed;
+		for (int i = 0; i < num_bits; ++i) {
+			operator ()();
+		}
+		out = static_cast<T>(state);
+	}
+
+private:
+	std::uint64_t state;
+	// bits 64, 63, 61, and 60 set to 1 (counting from 1 lo to hi)
+	static constexpr std::uint64_t mask = 0xD800000000000000;
+
+};
+
 /// (3D only) adaptation of Stefan Gustavson's SimplexNoise java class
 class SimplexNoise {
 
-- 
2.39.2