add project Unofficial.laszip.netstandard (cointaining latest snapshot of devel branch of https://github.com/shintadono/laszip.net which supposedly supports laszip 1.4)

Author: stefanmaierhofer

src/Unofficial.laszip.netstandard/ArithmeticBitModel.cs

@@ -0,0 +1,112 @@
+//===============================================================================
+//
+//  FILE:  arithmeticbitmodel.cs
+//
+//  CONTENTS:
+//
+//    C# port of a modular C++ wrapper for an adapted version of Amir Said's FastAC Code.
+//    see: http://www.cipr.rpi.edu/~said/FastAC.html
+//
+//  PROGRAMMERS:
+//
+//    martin.isenburg@rapidlasso.com  -  http://rapidlasso.com
+//
+//  COPYRIGHT:
+//
+//    (c) 2005-2017, martin isenburg, rapidlasso - fast tools to catch reality
+//    (c) of the C# port 2014-2017 by Shinta <shintadono@googlemail.com>
+//
+//    This is free software; you can redistribute and/or modify it under the
+//    terms of the GNU Lesser General Licence as published by the Free Software
+//    Foundation. See the COPYING file for more information.
+//
+//    This software is distributed WITHOUT ANY WARRANTY and without even the
+//    implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+//  CHANGE HISTORY: omitted for easier Copy&Paste (pls see the original)
+//
+//===============================================================================
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+//                                                                           -
+// Fast arithmetic coding implementation                                     -
+// -> 32-bit variables, 32-bit product, periodic updates, table decoding     -
+//                                                                           -
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+//                                                                           -
+// Version 1.00  -  April 25, 2004                                           -
+//                                                                           -
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+//                                                                           -
+//                                  WARNING                                  -
+//                                 =========                                 -
+//                                                                           -
+// The only purpose of this program is to demonstrate the basic principles   -
+// of arithmetic coding. It is provided as is, without any express or        -
+// implied warranty, without even the warranty of fitness for any particular -
+// purpose, or that the implementations are correct.                         -
+//                                                                           -
+// Permission to copy and redistribute this code is hereby granted, provided -
+// that this warning and copyright notices are not removed or altered.       -
+//                                                                           -
+// Copyright (c) 2004 by Amir Said (said@ieee.org) &                         -
+//                       William A. Pearlman (pearlw@ecse.rpi.edu)           -
+//                                                                           -
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+//                                                                           -
+// A description of the arithmetic coding method used here is available in   -
+//                                                                           -
+// Lossless Compression Handbook, ed. K. Sayood                              -
+// Chapter 5: Arithmetic Coding (A. Said), pp. 101-152, Academic Press, 2003 -
+//                                                                           -
+// A. Said, Introduction to Arithetic Coding Theory and Practice             -
+// HP Labs report HPL-2004-76  -  http://www.hpl.hp.com/techreports/         -
+//                                                                           -
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+namespace LASzip.Net
+{
+	class ArithmeticBitModel
+	{
+		public ArithmeticBitModel()
+		{
+			init();
+		}
+
+		public int init()
+		{
+			// initialization to equiprobable model
+			bit_0_count = 1;
+			bit_count = 2;
+			bit_0_prob = 1u << (BM.LengthShift - 1);
+
+			// start with frequent updates
+			update_cycle = bits_until_update = 4;
+
+			return 0;
+		}
+
+		internal void update()
+		{
+			// halve counts when a threshold is reached
+			if ((bit_count += update_cycle) > BM.MaxCount)
+			{
+				bit_count = (bit_count + 1) >> 1;
+				bit_0_count = (bit_0_count + 1) >> 1;
+				if (bit_0_count == bit_count) ++bit_count;
+			}
+
+			// compute scaled bit 0 probability
+			uint scale = 0x80000000u / bit_count;
+			bit_0_prob = (bit_0_count * scale) >> (31 - BM.LengthShift);
+
+			// set frequency of model updates
+			update_cycle = (5 * update_cycle) >> 2;
+			if (update_cycle > 64) update_cycle = 64;
+			bits_until_update = update_cycle;
+		}
+
+		internal uint update_cycle, bits_until_update;
+		internal uint bit_0_prob, bit_0_count, bit_count;
+	}
+}