Fixed issue: #47

core/src/main/java/org/luaj/vm2/libs/ApproxLib.java

@@ -0,0 +1,51 @@
+package org.luaj.vm2.libs;
+
+import org.luaj.vm2.LuaTable;
+import org.luaj.vm2.LuaValue;
+
+/**
+ * Optional helpers for approximate floating-point comparisons.
+ * This deliberately does not change Lua's core equality semantics.
+ */
+public class ApproxLib extends TwoArgFunction {
+
+	private static final double DEFAULT_EPSILON = 1e-9d;
+
+	public LuaValue call(LuaValue modname, LuaValue env) {
+		LuaTable lib = new LuaTable(0, 2);
+		lib.set("eq", new approx_eq());
+		env.set("approx", lib);
+		env.set("approx_eq", lib.get("eq"));
+		return lib;
+	}
+
+	static final class approx_eq extends VarArgFunction {
+		public LuaValue invoke(org.luaj.vm2.Varargs args) {
+			double a = args.checkdouble(1);
+			double b = args.checkdouble(2);
+			double epsilon = args.optdouble(3, DEFAULT_EPSILON);
+			if (epsilon < 0d) {
+				argerror(3, "epsilon must be >= 0");
+			}
+			return LuaValue.valueOf(approxEqual(a, b, epsilon));
+		}
+	}
+
+	public static boolean approxEqual(double a, double b, double epsilon) {
+		if (Double.doubleToLongBits(a) == Double.doubleToLongBits(b)) {
+			return true;
+		}
+		if (Double.isNaN(a) || Double.isNaN(b)) {
+			return false;
+		}
+		if (Double.isInfinite(a) || Double.isInfinite(b)) {
+			return false;
+		}
+		double diff = Math.abs(a - b);
+		if (diff <= epsilon) {
+			return true;
+		}
+		double scale = Math.max(Math.abs(a), Math.abs(b));
+		return diff <= scale * epsilon;
+	}
+}