added Evaluator.cs

OpenRA.FileFormats/Evaluator.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenRA.FileFormats
+{
+	public static class Evaluator
+	{
+		public static int Evaluate(string expr)
+		{
+			return Evaluate(expr, new Dictionary<string, int>());
+		}
+
+		public static int Evaluate(string expr, Dictionary<string, int> syms)
+		{
+			var toks = Tokens(expr, "+-*/()");
+			var postfix = ToPostfix(toks, syms);
+
+			var s = new Stack<int>();
+
+			foreach (var t in postfix)
+			{
+				switch (t[0])
+				{
+					case '+': ApplyBinop(s, (x, y) => x + y); break;
+					case '-': ApplyBinop(s, (x, y) => x - y); break;
+					case '*': ApplyBinop(s, (x, y) => x * y); break;
+					case '/': ApplyBinop(s, (x, y) => x / y); break;
+					default: s.Push(int.Parse(t)); break;
+				}
+			}
+
+			return s.Pop();
+		}
+
+		static void ApplyBinop( Stack<int> s, Func<int,int,int> f )
+		{
+			var x = s.Pop();
+			var y = s.Pop();
+			s.Push( f(x,y) );
+		}
+
+		static IEnumerable<string> ToPostfix(IEnumerable<string> toks, Dictionary<string, int> syms)
+		{
+			var s = new Stack<string>();
+
+			foreach (var t in toks)
+			{
+				if (t[0] == '(') s.Push(t);
+				else if (t[0] == ')')
+				{
+					var temp = "";
+					while ((temp = s.Pop()) != "(") yield return temp;
+				}
+				else if (char.IsNumber(t[0])) yield return t;
+				else if (char.IsLetter(t[0])) yield return syms[t].ToString();
+				else
+				{
+					while (s.Count > 0 && Prec[t] <= Prec[s.Peek()]) yield return s.Pop();
+					s.Push(t);
+				}
+			}
+
+			while (s.Count > 0) yield return s.Pop();
+		}
+
+		static readonly Dictionary<string, int> Prec
+			= new Dictionary<string, int> { { "+", 0 }, { "-", 0 }, { "*", 1 }, { "/", 1 } };
+
+		static IEnumerable<string> Tokens(string expr, string ops)
+		{
+			var s = "";
+			foreach (var c in expr)
+			{
+				if (char.IsWhiteSpace(c))
+				{
+					if (s != "") yield return s;
+					s = "";
+				}
+				else if (ops.Contains(c))
+				{
+					if (s != "") yield return s;
+					s = "";
+					yield return "" + c;
+				}
+				else
+					s += c;
+			}
+
+			if (s != "") yield return s;
+		}
+	}
+}