diff --git a/README.md b/README.md
index 6f9f289..2007bd6 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # java.math.expression.parser
 java math expression parser is a maven project that lets you parse or evaluate math expressions.
 
-This algorithm does not use a decision tree. It is a kind of Recursive Ascent Parser (https://en.wikipedia.org/wiki/Recursive_ascent_parser). In fact, it is LR parser (Left-Right Parser) without backtracking.
+This algorithm does not use a decision tree. It is a kind of Recursive Descent Parser (https://en.wikipedia.org/wiki/Recursive_descent_parser). In fact, it is LR parser (Left-Right Parser) without backtracking.
 
 This algorithm is faster than JEP math expresion parser!!! If you compare java.math.expression.parse and JEP, this algorithm only needs 25% of the time to parse the same expression as JEP. With other algorithms that use trees like:
 
@@ -90,14 +90,17 @@ This algorithm is faster than JEP math expresion parser!!! If you compare java.m
  
        These are the results for the version 3.0 (master). You can check the speedTests in the project
   
-	   Parser.simpleEval("6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4
-	   + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4");
+	   Parser.simpleEval("6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3
+                              + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 
+			      -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4");
 
        CPU: i7-6500U
        
-       test 1: one execution: 4ms
+       test 1: one execution: 3ms
        test 2: 100000 executions : 2100 ms --> mean time 0.021 ms per execution 
-       test 3: one million executions: 16500 ms --> mean time 0.0165 ms per execution
+                                   (with graalvm-jdk-17.0.8+9.1 the total time is 754ms --> 0.00754 per execution) 
+       test 3: one million executions: 16500 ms --> mean time 0.0165 ms per execution 
+                                   (with graalvm-jdk-17.0.8+9.1 the total time is 7980ms --> 0,00798 per execution) 
 
 
 This version is compiled for Java 1.6
diff --git a/pom.xml b/pom.xml
index 4f5b566..7fd17c3 100644
--- a/pom.xml
+++ b/pom.xml
@@ -4,7 +4,7 @@
 	<groupId>com.expression.parser</groupId>
 	<artifactId>com.expression.parser</artifactId>
 	<packaging>jar</packaging>
-	<version>3.0.0</version>
+	<version>3.3.0</version>
 	<name>com.expression.parser</name>
 	<description></description>
 	
diff --git a/src/main/java/com/expression/parser/function/ComplexFunction.java b/src/main/java/com/expression/parser/function/ComplexFunction.java
index b5bc594..739b0cb 100644
--- a/src/main/java/com/expression/parser/function/ComplexFunction.java
+++ b/src/main/java/com/expression/parser/function/ComplexFunction.java
@@ -6,7 +6,6 @@
 import com.expression.parser.ParserManager;
 import com.expression.parser.exception.CalculatorException;
 
-// TODO: Auto-generated Javadoc
 /**
  * The Class ComplexFunction.
  */
@@ -90,7 +89,7 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 			if (character >= '0' && character <= '9') {
 
 				hasNumber = true;
-				number = number + character;
+				number += character;
 				if (i == (f.length() - 1)) {
 					value = new Complex(new Double(number), 0);
 					number = "";
@@ -103,28 +102,28 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = f.substring(i + 1, f.length());
 					value = Complex.add(new Complex(numb, 0), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasNumber && isImaginary) {
 					final Double numb = new Double(number);
 					final String new_f = f.substring(i + 1, f.length());
 					value = Complex.add(new Complex(0, numb), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					isImaginary = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = f.substring(i + 1, f.length());
 					value = Complex.add(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = f.substring(i + 1, f.length());
 					value = Complex.add(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '*') {
@@ -133,7 +132,7 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.mul(new Complex(numb, 0), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 
@@ -141,20 +140,20 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.mul(new Complex(0, numb), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					isImaginary = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.mul(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.mul(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '-') {
@@ -163,14 +162,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = Complex.sub(new Complex(numb, 0), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasNumber && isImaginary) {
 					final Double numb = new Double(number);
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = Complex.sub(new Complex(0, numb), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					isImaginary = false;
 					number = "";
@@ -178,14 +177,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 				} else if (hasFunction) {
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = Complex.sub(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = Complex.sub(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '/') {
@@ -194,14 +193,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.div(new Complex(numb, 0), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasNumber && isImaginary) {
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.div(new Complex(0, numb), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					isImaginary = false;
 					number = "";
@@ -209,14 +208,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.div(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.div(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '^') {
@@ -225,14 +224,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.pow(eval(new_f, values, variables), numb);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasNumber && isImaginary) {
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.pow(eval(new_f, values, variables), new Complex(0, numb));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					isImaginary = false;
 					number = "";
@@ -240,14 +239,14 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.pow(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = Complex.pow(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '.') {
@@ -255,7 +254,7 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					throw new CalculatorException("The function is not well-formed");
 				}
 				if (hasNumber && (number.length() > 0)) {
-					number = number + character;
+					number += character;
 				}
 
 			} else if (character == '(') {
@@ -265,39 +264,39 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 
 				final String new_f = f.substring(i + 1, nextBracket(f));
 				if (hasFunction) {
-					if (function.equals(Constants.SIN)) {
+					if (Constants.SIN.equals(function)) {
 						value = eval(new_f, values, variables).sin();
 
-					} else if (function.equals(Constants.COS)) {
+					} else if (Constants.COS.equals(function)) {
 						value = eval(new_f, values, variables).cos();
 
-					} else if (function.equals(Constants.TAN)) {
+					} else if (Constants.TAN.equals(function)) {
 						value = eval(new_f, values, variables).tan();
 
-					} else if (function.equals(Constants.SINH)) {
+					} else if (Constants.SINH.equals(function)) {
 						value = eval(new_f, values, variables).sinh();
 
-					} else if (function.equals(Constants.COSH)) {
+					} else if (Constants.COSH.equals(function)) {
 						value = eval(new_f, values, variables).cosh();
 
-					} else if (function.equals(Constants.TANH)) {
+					} else if (Constants.TANH.equals(function)) {
 						value = eval(new_f, values, variables).tanh();
 
-					} else if (function.equals(Constants.ASIN)) {
+					} else if (Constants.ASIN.equals(function)) {
 						value = eval(new_f, values, variables).asin();
 
-					} else if (function.equals(Constants.ACOS)) {
+					} else if (Constants.ACOS.equals(function)) {
 						value = eval(new_f, values, variables).acos();
 
-					} else if (function.equals(Constants.ATAN)) {
+					} else if (Constants.ATAN.equals(function)) {
 						value = eval(new_f, values, variables).atan();
-					} else if (function.equals(Constants.LN)) {
+					} else if (Constants.LN.equals(function)) {
 						value = eval(new_f, values, variables).log();
-					} else if (function.equals(Constants.LOG)) {
+					} else if (Constants.LOG.equals(function)) {
 						value = eval(new_f, values, variables).log10();
-					} else if (function.equals(Constants.SQRT)) {
+					} else if (Constants.SQRT.equals(function)) {
 						value = eval(new_f, values, variables).sqrt();
-					} else if (function.equals(Constants.CBRT)) {
+					} else if (Constants.CBRT.equals(function)) {
 						value = Complex.cbrt(eval(new_f, values, variables));
 					} else {
 						throw new CalculatorException("The function is not well-formed");
@@ -309,7 +308,7 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 				} else {
 					value = eval(new_f, values, variables);
 				}
-				i = i + new_f.length() + 1;
+				i += new_f.length() + 1;
 
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
@@ -334,10 +333,10 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 
 					if (i == (f.length() - 1)) {
 
-						if (function.equals(Constants.E)) {
-							value = new Complex(Math.E, 0);
-						} else if (function.equals(Constants.PI)) {
-							value = new Complex(Math.PI, 0);
+						if (Constants.E.equals(function)) {
+							value = new Complex(StrictMath.E, 0);
+						} else if (Constants.PI.equals(function)) {
+							value = new Complex(StrictMath.PI, 0);
 						} else {
 							if (function.length() == 1) {
 								final int n = variables.indexOf(function);
@@ -370,9 +369,9 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 					if (i == (f.length() - 1)) {
 
 						if (function.equals(Constants.E)) {
-							value = new Complex(Math.E, 0);
+							value = new Complex(StrictMath.E, 0);
 						} else if (function.equals(Constants.PI)) {
-							value = new Complex(Math.PI, 0);
+							value = new Complex(StrictMath.PI, 0);
 						} else {
 							if (function.length() == 1) {
 								final int n = variables.indexOf(function);
@@ -396,11 +395,11 @@ private Complex eval(final String f, final List<Complex> values, final List<Stri
 
 				if (i == (f.length() - 1)) {
 
-					if (function.equals(Constants.E)) {
-						value = new Complex(Math.E, 0);
+					if (Constants.E.equals(function)) {
+						value = new Complex(StrictMath.E, 0);
 
-					} else if (function.equals(Constants.PI)) {
-						value = new Complex(Math.PI, 0);
+					} else if (Constants.PI.equals(function)) {
+						value = new Complex(StrictMath.PI, 0);
 					} else {
 						if (function.length() == 1) {
 							final int n = variables.indexOf(function);
@@ -436,22 +435,20 @@ private String nextFunction(final String f) throws CalculatorException {
 		for (int i = 0; i < f.length(); i++) {
 			final char character = f.charAt(i);
 
-			if (character == '+' || character == '*' || character == '-' || character == '/') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '*' || character == '-' || character == '/') {
 				i = f.length();
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f = f.substring(i, nextBracket(f) + 1);
-				result = result + new_f;
+				result += new_f;
 				i = (i + new_f.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
@@ -473,28 +470,20 @@ private String nextMinusFunction(final String f) throws CalculatorException {
 		for (int i = 0; i < f.length(); i++) {
 			final char character = f.charAt(i);
 
-			if (character == '+') {
-				i = f.length();
-			} else if (character == '*') {
-				result = result + character;
-			} else if (character == '-') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '-') {
 				i = f.length();
-			} else if (character == '/') {
-				result = result + character;
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '*' || character == '/' || character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f = f.substring(i, nextBracket(f) + 1);
-				result = result + new_f;
+				result += new_f;
 				i = (i + new_f.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
diff --git a/src/main/java/com/expression/parser/function/FunctionX.java b/src/main/java/com/expression/parser/function/FunctionX.java
index 6092973..f57ba25 100644
--- a/src/main/java/com/expression/parser/function/FunctionX.java
+++ b/src/main/java/com/expression/parser/function/FunctionX.java
@@ -74,7 +74,7 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 			if (character >= '0' && character <= '9') {
 
 				hasNumber = true;
-				number = number + character;
+				number += character;
 				if (i == (f_x.length() - 1)) {
 					value = new Double(number).doubleValue();
 					number = "";
@@ -87,19 +87,19 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 					final Double numb = new Double(number);
 					final String new_f_x = f_x.substring(i + 1, f_x.length());
 					value = numb + eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f_x = f_x.substring(i + 1, f_x.length());
 					value = eval(function, xi) + eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f_x = f_x.substring(i + 1, f_x.length());
 					value = value + eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 				}
 
 			} else if (character == '*') {
@@ -108,19 +108,19 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 					final Double numb = new Double(number);
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = numb * eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = eval(function, xi) * eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = value * eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 				}
 
 			} else if (character == '-') {
@@ -129,19 +129,19 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 					final Double numb = new Double(number);
 					final String new_f_x = nextMinusFunction(f_x.substring(i + 1, f_x.length()));
 					value = numb - eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f_x = nextMinusFunction(f_x.substring(i + 1, f_x.length()));
 					value = eval(function, xi) - eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f_x = nextMinusFunction(f_x.substring(i + 1, f_x.length()));
 					value = value - eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 				}
 
 			} else if (character == '/') {
@@ -150,19 +150,19 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 					final Double numb = new Double(number);
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = numb / eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = eval(function, xi) / eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
 					value = value / eval(new_f_x, xi);
-					i = i + new_f_x.length();
+					i += new_f_x.length();
 				}
 
 			} else if (character == '^') {
@@ -170,20 +170,20 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 				if (hasNumber) {
 					final Double numb = new Double(number);
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
-					value = Math.pow(numb.doubleValue(), eval(new_f_x, xi));
-					i = i + new_f_x.length();
+					value = StrictMath.pow(numb.doubleValue(), eval(new_f_x, xi));
+					i += new_f_x.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
-					value = Math.pow(eval(function, xi), eval(new_f_x, xi));
-					i = i + new_f_x.length();
+					value = StrictMath.pow(eval(function, xi), eval(new_f_x, xi));
+					i += new_f_x.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f_x = nextFunction(f_x.substring(i + 1, f_x.length()));
-					value = Math.pow(value, eval(new_f_x, xi));
-					i = i + new_f_x.length();
+					value = StrictMath.pow(value, eval(new_f_x, xi));
+					i += new_f_x.length();
 				}
 
 			} else if (character == '.') {
@@ -192,7 +192,7 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 					throw new CalculatorException("The function is not well-formed");
 				}
 				if (hasNumber && (number.length() > 0)) {
-					number = number + character;
+					number += character;
 				}
 
 			} else if (character == '(') {
@@ -202,65 +202,65 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 
 				final String new_f_x = f_x.substring(i + 1, nextBracket(f_x));
 				if (hasFunction) {
-					if (function.equals(Constants.SIN)) {
+					if (Constants.SIN.equals(function)) {
 
 						if (degree) {
-							value = Math.sin(Math.toRadians(eval(new_f_x, xi)));
+							value = StrictMath.sin(StrictMath.toRadians(eval(new_f_x, xi)));
 						} else {
-							value = Math.sin(eval(new_f_x, xi));
+							value = StrictMath.sin(eval(new_f_x, xi));
 						}
 
-					} else if (function.equals(Constants.COS)) {
+					} else if (Constants.COS.equals(function)) {
 
 						if (degree) {
-							value = Math.cos(Math.toRadians(eval(new_f_x, xi)));
+							value = StrictMath.cos(StrictMath.toRadians(eval(new_f_x, xi)));
 						} else {
-							value = Math.cos(eval(new_f_x, xi));
+							value = StrictMath.cos(eval(new_f_x, xi));
 						}
 
-					} else if (function.equals(Constants.TAN)) {
+					} else if (Constants.TAN.equals(function)) {
 
 						if (degree) {
-							value = Math.tan(Math.toRadians(eval(new_f_x, xi)));
+							value = StrictMath.tan(StrictMath.toRadians(eval(new_f_x, xi)));
 						} else {
-							value = Math.tan(eval(new_f_x, xi));
+							value = StrictMath.tan(eval(new_f_x, xi));
 						}
 
-					} else if (function.equals(Constants.SINH)) {
-						value = Math.sinh(eval(new_f_x, xi));
+					} else if (Constants.SINH.equals(function)) {
+						value = StrictMath.sinh(eval(new_f_x, xi));
 
-					} else if (function.equals(Constants.COSH)) {
-						value = Math.cosh(eval(new_f_x, xi));
+					} else if (Constants.COSH.equals(function)) {
+						value = StrictMath.cosh(eval(new_f_x, xi));
 
-					} else if (function.equals(Constants.TANH)) {
-						value = Math.tanh(eval(new_f_x, xi));
+					} else if (Constants.TANH.equals(function)) {
+						value = StrictMath.tanh(eval(new_f_x, xi));
 
-					} else if (function.equals(Constants.ASIN)) {
+					} else if (Constants.ASIN.equals(function)) {
 						if (degree) {
-							value = Math.asin(eval(new_f_x, xi)) * (180 / Math.PI);
+							value = StrictMath.asin(eval(new_f_x, xi)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.asin(eval(new_f_x, xi));
+							value = StrictMath.asin(eval(new_f_x, xi));
 						}
-					} else if (function.equals(Constants.ACOS)) {
+					} else if (Constants.ACOS.equals(function)) {
 						if (degree) {
-							value = Math.acos(eval(new_f_x, xi)) * (180 / Math.PI);
+							value = StrictMath.acos(eval(new_f_x, xi)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.acos(eval(new_f_x, xi));
+							value = StrictMath.acos(eval(new_f_x, xi));
 						}
-					} else if (function.equals(Constants.ATAN)) {
+					} else if (Constants.ATAN.equals(function)) {
 						if (degree) {
-							value = Math.atan(eval(new_f_x, xi)) * (180 / Math.PI);
+							value = StrictMath.atan(eval(new_f_x, xi)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.atan(eval(new_f_x, xi));
+							value = StrictMath.atan(eval(new_f_x, xi));
 						}
-					} else if (function.equals(Constants.LN)) {
-						value = Math.log(eval(new_f_x, xi));
-					} else if (function.equals(Constants.LOG)) {
-						value = Math.log10(eval(new_f_x, xi));
-					} else if (function.equals(Constants.SQRT)) {
-						value = Math.sqrt(eval(new_f_x, xi));
-					} else if (function.equals(Constants.CBRT)) {
-						value = Math.cbrt(eval(new_f_x, xi));
+					} else if (Constants.LN.equals(function)) {
+						value = StrictMath.log(eval(new_f_x, xi));
+					} else if (Constants.LOG.equals(function)) {
+						value = StrictMath.log10(eval(new_f_x, xi));
+					} else if (Constants.SQRT.equals(function)) {
+						value = StrictMath.sqrt(eval(new_f_x, xi));
+					} else if (Constants.CBRT.equals(function)) {
+						value = StrictMath.cbrt(eval(new_f_x, xi));
 					} else {
 						throw new CalculatorException("The function is not well-formed");
 					}
@@ -271,35 +271,34 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 				} else {
 					value = eval(new_f_x, xi);
 				}
-				i = i + new_f_x.length() + 1;
-
-			} else if (character == ')') {
-				throw new CalculatorException(" '(' is not finished ");
-
-			} else if (character == ' ') {
+				i += new_f_x.length() + 1;
 
 			} else if (isValidCharacter(character)) {
 				function = function + character;
 				hasFunction = true;
 
 				if (i == (f_x.length() - 1)) {
-					if (function.equals(Constants.E)) {
-						value = Math.E;
-					} else if (function.equals(Constants.PI)) {
-						value = Math.PI;
+					if (Constants.E.equals(function)) {
+						value = StrictMath.E;
+					} else if (Constants.PI.equals(function)) {
+						value = StrictMath.PI;
 					} else if (function.length() == 1) {
 						value = xi;
 					} else {
 						throw new CalculatorException("function is not well defined");
 					}
 				}
+
+			} else if (character == ')') {
+				throw new CalculatorException(" '(' is not finished ");
+
+			} else if (character == ' ') {
+
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
-
 		}
 		return value;
-
 	}
 
 	/**
@@ -309,30 +308,26 @@ private double eval(final String f_x, final double xi) throws CalculatorExceptio
 	 * @return the string
 	 * @throws CalculatorException the calculator exception
 	 */
-	private String nextFunction(String f_x) throws CalculatorException {
+	private String nextFunction(final String f_x) throws CalculatorException {
 		String result = "";
-		f_x = f_x.trim().toLowerCase();
 
 		for (int i = 0; i < f_x.length(); i++) {
 			final char character = f_x.charAt(i);
 
-			if (character == '+' || character == '*' || character == '-' || character == '/') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '*' || character == '-' || character == '/') {
 				i = f_x.length();
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f_x = f_x.substring(i, nextBracket(f_x) + 1);
-				result = result + new_f_x;
+				result += new_f_x;
 				i = (i + new_f_x.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
-
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
@@ -352,28 +347,20 @@ private String nextMinusFunction(final String f_x) throws CalculatorException {
 		for (int i = 0; i < f_x.length(); i++) {
 			final char character = f_x.charAt(i);
 
-			if (character == '+') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '-') {
 				i = f_x.length();
-			} else if (character == '*') {
-				result = result + character;
-			} else if (character == '-') {
-				i = f_x.length();
-			} else if (character == '/') {
-				result = result + character;
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '*' || character == '/' || character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f_x = f_x.substring(i, nextBracket(f_x) + 1);
-				result = result + new_f_x;
+				result += new_f_x;
 				i = (i + new_f_x.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
@@ -430,7 +417,6 @@ private int nextBracket(final String f_x) throws CalculatorException {
 				if (count == 0) {
 					return i;
 				}
-
 			} else {
 				result = i;
 			}
diff --git a/src/main/java/com/expression/parser/function/FunctionXs.java b/src/main/java/com/expression/parser/function/FunctionXs.java
index 384ef79..0322cfa 100644
--- a/src/main/java/com/expression/parser/function/FunctionXs.java
+++ b/src/main/java/com/expression/parser/function/FunctionXs.java
@@ -86,7 +86,7 @@ private double eval(final String f, final List<Double> values, final List<String
 			if (character >= '0' && character <= '9') {
 
 				hasNumber = true;
-				number = number + character;
+				number += character;
 				if (i == (f.length() - 1)) {
 					value = new Double(number).doubleValue();
 					number = "";
@@ -99,20 +99,20 @@ private double eval(final String f, final List<Double> values, final List<String
 					final Double numb = new Double(number);
 					final String new_f = f.substring(i + 1, f.length());
 					value = numb + eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = f.substring(i + 1, f.length());
 					value = eval(function, values, variables) + eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = f.substring(i + 1, f.length());
 					value = value + eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '*') {
@@ -121,19 +121,19 @@ private double eval(final String f, final List<Double> values, final List<String
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = numb * eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = eval(function, values, variables) * eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = value * eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '-') {
@@ -142,20 +142,20 @@ private double eval(final String f, final List<Double> values, final List<String
 					final Double numb = new Double(number);
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = numb - eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = eval(function, values, variables) - eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextMinusFunction(f.substring(i + 1, f.length()));
 					value = value - eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '/') {
@@ -164,20 +164,20 @@ private double eval(final String f, final List<Double> values, final List<String
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = numb / eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = eval(function, values, variables) / eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
 					value = value / eval(new_f, values, variables);
-					i = i + new_f.length();
+					i += new_f.length();
 				}
 
 			} else if (character == '^') {
@@ -185,21 +185,21 @@ private double eval(final String f, final List<Double> values, final List<String
 				if (hasNumber) {
 					final Double numb = new Double(number);
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
-					value = Math.pow(numb.doubleValue(), eval(new_f, values, variables));
-					i = i + new_f.length();
+					value = StrictMath.pow(numb.doubleValue(), eval(new_f, values, variables));
+					i += new_f.length();
 					hasNumber = false;
 					number = "";
 				} else if (hasFunction) {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
-					value = Math.pow(eval(function, values, variables), eval(new_f, values, variables));
-					i = i + new_f.length();
+					value = StrictMath.pow(eval(function, values, variables), eval(new_f, values, variables));
+					i += new_f.length();
 					hasFunction = false;
 					function = "";
 
 				} else {
 					final String new_f = nextFunction(f.substring(i + 1, f.length()));
-					value = Math.pow(value, eval(new_f, values, variables));
-					i = i + new_f.length();
+					value = StrictMath.pow(value, eval(new_f, values, variables));
+					i += new_f.length();
 				}
 
 			} else if (character == '.') {
@@ -207,7 +207,7 @@ private double eval(final String f, final List<Double> values, final List<String
 					throw new CalculatorException("The function is not well-formed");
 				}
 				if (hasNumber && (number.length() > 0)) {
-					number = number + character;
+					number += character;
 				}
 
 			} else if (character == '(') {
@@ -217,61 +217,61 @@ private double eval(final String f, final List<Double> values, final List<String
 
 				final String new_f = f.substring(i + 1, nextBracket(f));
 				if (hasFunction) {
-					if (function.equals(Constants.SIN)) {
+					if (Constants.SIN.equals(function)) {
 						if (degree) {
-							value = Math.sin(Math.toRadians(eval(new_f, values, variables)));
+							value = StrictMath.sin(StrictMath.toRadians(eval(new_f, values, variables)));
 						} else {
-							value = Math.sin(eval(new_f, values, variables));
+							value = StrictMath.sin(eval(new_f, values, variables));
 						}
 
-					} else if (function.equals(Constants.COS)) {
+					} else if (Constants.COS.equals(function)) {
 						if (degree) {
-							value = Math.cos(Math.toRadians(eval(new_f, values, variables)));
+							value = StrictMath.cos(StrictMath.toRadians(eval(new_f, values, variables)));
 						} else {
-							value = Math.cos(eval(new_f, values, variables));
+							value = StrictMath.cos(eval(new_f, values, variables));
 						}
-					} else if (function.equals(Constants.TAN)) {
+					} else if (Constants.TAN.equals(function)) {
 						if (degree) {
-							value = Math.tan(Math.toRadians(eval(new_f, values, variables)));
+							value = StrictMath.tan(StrictMath.toRadians(eval(new_f, values, variables)));
 						} else {
-							value = Math.tan(eval(new_f, values, variables));
+							value = StrictMath.tan(eval(new_f, values, variables));
 						}
 
-					} else if (function.equals(Constants.SINH)) {
-						value = Math.sinh(eval(new_f, values, variables));
+					} else if (Constants.SINH.equals(function)) {
+						value = StrictMath.sinh(eval(new_f, values, variables));
 
-					} else if (function.equals(Constants.COSH)) {
-						value = Math.cosh(eval(new_f, values, variables));
+					} else if (Constants.COSH.equals(function)) {
+						value = StrictMath.cosh(eval(new_f, values, variables));
 
-					} else if (function.equals(Constants.TANH)) {
-						value = Math.tanh(eval(new_f, values, variables));
+					} else if (Constants.TANH.equals(function)) {
+						value = StrictMath.tanh(eval(new_f, values, variables));
 
-					} else if (function.equals(Constants.ASIN)) {
+					} else if (Constants.ASIN.equals(function)) {
 						if (degree) {
-							value = Math.asin(eval(new_f, values, variables)) * (180 / Math.PI);
+							value = StrictMath.asin(eval(new_f, values, variables)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.asin(eval(new_f, values, variables));
+							value = StrictMath.asin(eval(new_f, values, variables));
 						}
-					} else if (function.equals(Constants.ACOS)) {
+					} else if (Constants.ACOS.equals(function)) {
 						if (degree) {
-							value = Math.acos(eval(new_f, values, variables)) * (180 / Math.PI);
+							value = StrictMath.acos(eval(new_f, values, variables)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.acos(eval(new_f, values, variables));
+							value = StrictMath.acos(eval(new_f, values, variables));
 						}
-					} else if (function.equals(Constants.ATAN)) {
+					} else if (Constants.ATAN.equals(function)) {
 						if (degree) {
-							value = Math.atan(eval(new_f, values, variables)) * (180 / Math.PI);
+							value = StrictMath.atan(eval(new_f, values, variables)) * (180 / StrictMath.PI);
 						} else {
-							value = Math.atan(eval(new_f, values, variables));
+							value = StrictMath.atan(eval(new_f, values, variables));
 						}
-					} else if (function.equals(Constants.LN)) {
-						value = Math.log(eval(new_f, values, variables));
-					} else if (function.equals(Constants.LOG)) {
-						value = Math.log10(eval(new_f, values, variables));
-					} else if (function.equals(Constants.SQRT)) {
-						value = Math.sqrt(eval(new_f, values, variables));
-					} else if (function.equals(Constants.CBRT)) {
-						value = Math.cbrt(eval(new_f, values, variables));
+					} else if (Constants.LN.equals(function)) {
+						value = StrictMath.log(eval(new_f, values, variables));
+					} else if (Constants.LOG.equals(function)) {
+						value = StrictMath.log10(eval(new_f, values, variables));
+					} else if (Constants.SQRT.equals(function)) {
+						value = StrictMath.sqrt(eval(new_f, values, variables));
+					} else if (Constants.CBRT.equals(function)) {
+						value = StrictMath.cbrt(eval(new_f, values, variables));
 					} else {
 						throw new CalculatorException("The function is not well-formed");
 					}
@@ -282,23 +282,21 @@ private double eval(final String f, final List<Double> values, final List<String
 				} else {
 					value = eval(new_f, values, variables);
 				}
-				i = i + new_f.length() + 1;
+				i += new_f.length() + 1;
 
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 
-			} else if (character == ' ') {
-
 			} else if (isValidCharacter(character)) {
 				function = function + character;
 				hasFunction = true;
 
 				if (i == (f.length() - 1)) {
 
-					if (function.equals(Constants.E)) {
-						value = Math.E;
-					} else if (function.equals(Constants.PI)) {
-						value = Math.PI;
+					if (Constants.E.equals(function)) {
+						value = StrictMath.E;
+					} else if (Constants.PI.equals(function)) {
+						value = StrictMath.PI;
 					} else {
 						if (function.length() == 1) {
 							final int n = variables.indexOf(function);
@@ -314,6 +312,8 @@ private double eval(final String f, final List<Double> values, final List<String
 						}
 					}
 				}
+			} else if (character == ' ') {
+
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
@@ -334,22 +334,20 @@ private String nextFunction(final String f) throws CalculatorException {
 		for (int i = 0; i < f.length(); i++) {
 			final char character = f.charAt(i);
 
-			if (character == '+' || character == '*' || character == '-' || character == '/') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '*' || character == '-' || character == '/') {
 				i = f.length();
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f = f.substring(i, nextBracket(f) + 1);
-				result = result + new_f;
+				result += new_f;
 				i = (i + new_f.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
@@ -364,35 +362,26 @@ private String nextFunction(final String f) throws CalculatorException {
 	 * @return the string
 	 * @throws CalculatorException the calculator exception
 	 */
-	private String nextMinusFunction(String f) throws CalculatorException {
+	private String nextMinusFunction(final String f) throws CalculatorException {
 		String result = "";
-		f = f.trim().toLowerCase();
 
 		for (int i = 0; i < f.length(); i++) {
 			final char character = f.charAt(i);
 
-			if (character == '+') {
+			if (isValidNumericAndCharacter(character)) {
+				result += character;
+			} else if (character == '+' || character == '-') {
 				i = f.length();
-			} else if (character == '*') {
-				result = result + character;
-			} else if (character == '-') {
-				i = f.length();
-			} else if (character == '/') {
-				result = result + character;
-			} else if (character == '^') {
-				result = result + character;
-			} else if (character == '.') {
-				result = result + character;
+			} else if (character == '*' || character == '/' || character == '.' || character == '^') {
+				result += character;
 			} else if (character == '(') {
 				final String new_f = f.substring(i, nextBracket(f) + 1);
-				result = result + new_f;
+				result += new_f;
 				i = (i + new_f.length()) - 1;
 			} else if (character == ')') {
 				throw new CalculatorException(" '(' is not finished ");
 			} else if (character == ' ') {
-				result = result + character;
-			} else if (isValidNumericAndCharacter(character)) {
-				result = result + character;
+				result += character;
 			} else {
 				throw new CalculatorException("Invalid character:" + character);
 			}
diff --git a/src/test/java/com/expression/parser/SpeedTest.java b/src/test/java/com/expression/parser/SpeedTest.java
index 8be74eb..f62164f 100644
--- a/src/test/java/com/expression/parser/SpeedTest.java
+++ b/src/test/java/com/expression/parser/SpeedTest.java
@@ -20,7 +20,7 @@ public void testTwo() {
 
 		final long time1 = System.currentTimeMillis();
 
-		for (int i = 0; i < 100000; i++) {
+		for (int i = 0; i < 1000000; i++) {
 			Parser.simpleEval(
 					"6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4 + 6.5*7.8^2.3 + (3.5^3+7/2)^3 -(5*4/(2-3))*4");
 		}

<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN' 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'>
<html xmlns='http://www.w3.org/1999/xhtml'>
<head>
<title>pFad - Phonifier reborn</title>
<meta http-equiv='Content-Type' content='text/html; charset=utf-8' />
</head>
<body>
<h1>Pfad - The Proxy pFad of &#169; 2024 Garber Painting. All rights reserved.</h1>


<!-- Disclaimer -->
<p>Note: This service is not intended for secure transactions such as banking, social media, email, or purchasing. Use at your own risk. We assume no liability whatsoever for broken pages.</p>
<br>
<p>Alternative Proxies:</p><p><a href="http://rainy.clevelandohioweatherforecast.com/php-proxy/index.php?q=https://github.com/sbesada/java.math.expression.parser/compare/v3.0.0...master.diff" target="_blank">Alternative Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/index.php?u=https://github.com/sbesada/java.math.expression.parser/compare/v3.0.0...master.diff" target="_blank">pFad Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v3index.php?u=https://github.com/sbesada/java.math.expression.parser/compare/v3.0.0...master.diff" target="_blank">pFad v3 Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v4index.php?u=https://github.com/sbesada/java.math.expression.parser/compare/v3.0.0...master.diff" target="_blank">pFad v4 Proxy</a></p></body>
</html>