Statistical parsing of English sentences

//Copyright (C) 2005 Richard J. Northedge
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

//This file is based on the Span.java source file found in the
//original java implementation of OpenNLP.  That source file contains the following header:

// Copyright (C) 2002 Tom Morton
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

using System;

namespace OpenNLP.Tools.Util
{
	/// <summary>
	/// Class for storing start and end integer offsets.  
	/// </summary>
	
	public class Span : System.IComparable
	{
		private int mStart;
		private int mEnd;
		
		/// <summary>
		/// Return the start of a span.
		/// </summary>
		/// <returns> 
		/// the start of a span.
		/// </returns>
		virtual public int Start
		{
			get
			{
				return mStart;
			}
			
		}
		/// <summary>
		/// Return the end of a span.
		/// </summary>
		/// <returns> 
		/// the end of a span.
		/// </returns>
		virtual public int End
		{
			get
			{
				return mEnd;
			}
			
		}
		
		
		/// <summary>Constructs a new Span object.
		/// </summary>
		/// <param name="startOfSpan">
		/// start of span.
		/// </param>
		/// <param name="endOfSpan">
		/// end of span.
		/// </param>
		public Span(int startOfSpan, int endOfSpan)
		{
			mStart = startOfSpan;
			mEnd = endOfSpan;
		}
		
		public virtual int Length()
		{
			return (mEnd - mStart);
		}
		
		/// <summary>
		/// Returns true is the specified span is contained by this span.  
		/// Identical spans are considered to contain each other. 
		/// </summary>
		/// <param name="span">
		/// The span to compare with this span.
		/// </param>
		/// <returns>
		/// true if the specified span is contained by this span; false otherwise. 
		/// </returns>
		public virtual bool Contains(Span span)
		{
			return (mStart <= span.Start && span.End <= mEnd);
		}
		
		/// <summary>
		/// Returns true if the specified span intersects with this span.
		/// </summary>
		/// <param name="span">
		/// The span to compare with this span. 
		/// </param>
		/// <returns>
		/// true is the spans overlap; false otherwise. 
		/// </returns>
		public bool Intersects(Span span) 
		{
			int spanStart = span.Start;
			//either span's start is in this or this's start is in span
			return (this.Contains(span) || span.Contains(this) ||
				(mStart <= spanStart && spanStart < mEnd ||
				spanStart <= mStart && mStart < span.End));
		}
  
		/// <summary>
		/// Returns true if the specified span crosses this span.
		/// </summary>
		/// <param name="span">
		/// The span to compare with this span.
		/// </param>
		/// <returns>
		/// true if the specified span overlaps this span and contains a non-overlapping section; false otherwise.
		/// </returns>
		public bool Crosses(Span span) 
		{
			int spanStart = span.Start;
			//either span's Start is in this or this's Start is in span
			return (!this.Contains(span) && !span.Contains(this) && 
				(mStart <= spanStart && spanStart < mEnd ||
				spanStart <= mStart && mStart < span.End));
		}

		public virtual int CompareTo(object o) 
		{ 
			Span compareSpan = (Span) o;
			if (Start < compareSpan.Start) 
			{
				return -1;
			}
			else if (Start == compareSpan.Start) 
			{
				if (End > compareSpan.End) 
				{
					return -1;
				}
				else if (End < compareSpan.End) 
				{
					return 1;
				}
				else 
				{
					return 0;
				}
			}
			else 
			{
				return 1;
			}
		}

		public override int GetHashCode() 
		{
			return((Start << 16) | (0x0000FFFF | this.End));
		}
  
		public override bool Equals(object o) 
		{
			if (!(o is Span))
			{
				return false;
			}
			Span currentSpan = (Span) o;
			return(Start == currentSpan.Start && End == currentSpan.End);
		}

		public override string ToString()
		{
			System.Text.StringBuilder buffer = new System.Text.StringBuilder(15);
			return (buffer.Append(Start).Append("..").Append(End).ToString());
		}
	}
}