From 1e7a25e1a87af4a263ae2a150674607f646891ae Mon Sep 17 00:00:00 2001
From: Ahmet Inan <inan@aicodix.de>
Date: Tue, 31 Mar 2020 18:05:10 +0200
Subject: [PATCH] added maximum length sequence

---
 README.md |  4 ++++
 mls.hh    | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 mls.hh

diff --git a/README.md b/README.md
index a7d97c1..f05ce92 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,10 @@ Sometimes we need a sequence of ["random enough"](https://en.wikipedia.org/wiki/
 Here a [Pseudorandom number generator](https://en.wikipedia.org/wiki/Pseudorandom_number_generator) can help by prodiving a deterministic and thus repeatable sequence of numbers.
 [George Marsaglia](https://en.wikipedia.org/wiki/George_Marsaglia) discovered a class of simple and fast pseudorandom number generators, which he called [Xorshift](https://en.wikipedia.org/wiki/Xorshift).
 
+### [mls.hh](mls.hh)
+
+[Maximum length sequences](https://en.wikipedia.org/wiki/Maximum_length_sequence) have useful [correlation properties](https://en.wikipedia.org/wiki/Maximum_length_sequence#Correlation_property).
+
 ### [bitstream.hh](bitstream.hh)
 
 When dealing with unaligned and arbitrary-bit-sized elements in a data stream, the bitwise stream container might help avoiding some headaches.
diff --git a/mls.hh b/mls.hh
new file mode 100644
index 0000000..b1a3f19
--- /dev/null
+++ b/mls.hh
@@ -0,0 +1,35 @@
+/*
+Maximum length sequence
+
+Copyright 2020 Ahmet Inan <inan@aicodix.de>
+*/
+
+#pragma once
+
+namespace CODE {
+
+class MLS
+{
+	static int hibit(unsigned n)
+	{
+		n |= n >> 1;
+		n |= n >> 2;
+		n |= n >> 4;
+		n |= n >> 8;
+		n |= n >> 16;
+		return n ^ (n >> 1);
+	}
+	int poly, test, reg;
+public:
+	MLS(int poly = 0b100000000000000001001, int reg = 1) : poly(poly), test(hibit(poly)>>1), reg(reg) {}
+	bool operator()()
+	{
+		bool fb = reg & test;
+		reg <<= 1;
+		reg ^= fb * poly;
+		return fb;
+	}
+};
+
+}
+