Calculator operators ! and !! for factorial and double factorial

Author: mtommila

apfloat-calc/src/main/java/org/apfloat/calc/AbstractCalculatorImpl.java

@@ -1,7 +1,7 @@
 /*
  * MIT License
  *
- * Copyright (c) 2002-2023 Mikko Tommila
+ * Copyright (c) 2002-2024 Mikko Tommila
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -35,7 +35,7 @@
  * Provides a storage for variables, and maps
  * the elementary operators to function calls.
  *
- * @version 1.9.1
+ * @version 1.14.0
  * @author Mikko Tommila
  */
 
@@ -103,6 +103,20 @@ public Number pow(Number x, Number y)
         return function("pow", toList(x, y));
     }
 
+    @Override
+    public Number factorial(Number x)
+        throws ParseException
+    {
+        return function("factorial", toList(x));
+    }
+
+    @Override
+    public Number doubleFactorial(Number x)
+        throws ParseException
+    {
+        return function("doubleFactorial", toList(x));
+    }
+
     @Override
     public Number getVariable(String name)
         throws ParseException

apfloat-calc/src/main/java/org/apfloat/calc/CalculatorImpl.java

@@ -1,7 +1,7 @@
 /*
  * MIT License
  *
- * Copyright (c) 2002-2023 Mikko Tommila
+ * Copyright (c) 2002-2024 Mikko Tommila
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -29,7 +29,7 @@
  * Calculator implementation interface.
  * The calculator parser uses this interface to perform the actual calculations.
  *
- * @version 1.9.1
+ * @version 1.14.0
  * @author Mikko Tommila
  */
 
@@ -132,6 +132,32 @@ public Number mod(Number x, Number y)
     public Number pow(Number x, Number y)
         throws ParseException;
 
+    /**
+     * Factorial.
+     *
+     * @param x The argument.
+     *
+     * @return <code>x!</code>
+     *
+     * @exception ParseException In case of invalid arguments.
+     */
+
+    public Number factorial(Number x)
+        throws ParseException;
+
+    /**
+     * Double factorial.
+     *
+     * @param x The argument.
+     *
+     * @return <code>x!!</code>
+     *
+     * @exception ParseException In case of invalid arguments.
+     */
+
+    public Number doubleFactorial(Number x)
+        throws ParseException;
+
     /**
      * Arbitrary function.
      *

apfloat-calc/src/main/java/org/apfloat/calc/CalculatorParser.jj

@@ -163,13 +163,26 @@ Number powerExpression():
     Number b;
 }
 {
-    a = element()
+    a = factorialExpression()
     (
         "^" b = unaryExpression()               { a = this.calculatorImpl.pow(a, b); }
     )?
                                                 { return a; }
 }
 
+Number factorialExpression():
+{
+    Number a;
+}
+{
+    a = element()
+    (
+        "!!"                                    { a = this.calculatorImpl.doubleFactorial(a); }
+      | "!"                                     { a = this.calculatorImpl.factorial(a); }
+    )*
+                                                { return a; }
+}
+
 Number element():
 {
     String v;

apfloat-calc/src/test/java/org/apfloat/calc/CalculatorTest.java

@@ -167,6 +167,20 @@ public static void testOperators()
         assertCalculation("8.8080652584e646456992", "2^2147483647.0");
         assertCalculation("-1", "i^2");
         assertCalculation("1", "1^2i");
+        assertCalculation("2417851639229258349412352", "2^3^4");
+        assertCalculation("120", "5!");
+        assertCalculation("15", "5!!");
+        assertCalculation("64", "2^3!");
+        assertCalculation("8", "2^3!!");
+        assertCalculation("1307674368000", "5!!!");
+        assertCalculation("2027025", "5!!!!");
+        assertCalculation("-24", "-4!");
+        assertCalculation("1/16777216", "2^-4!");
+        assertCalculation("-1/16777216", "-2^-4!");
+        assertCalculation("8", "2^3!!!!");
+        assertCalculation("-1/8", "-2^-3!!!!");
+        assertCalculation("4", "2!^2!");
+        assertCalculation("4", "2!!^2!!");
 
         assertCalculationFailure("6%i");
         assertCalculationFailure("5e");
@@ -184,6 +198,11 @@ public static void testOperators()
         assertCalculationFailure("6%");
         assertCalculationFailure("2-");
         assertCalculationFailure("bogus^5");
+        assertCalculationFailure("!");
+        assertCalculationFailure("bogus!");
+        assertCalculationFailure("bogus!!");
+        assertCalculationFailure("5!=");
+        assertCalculationFailure("5!=4");
     }
 
     public static void testFunctions()

src/site/resources/applet/calculator-help.html

@@ -54,6 +54,8 @@ <h2>Operators</h2>
 <tr><td><code>/</code></td><td>division</td></tr>
 <tr><td><code>%</code></td><td>modulus</td></tr>
 <tr><td><code>^</code></td><td>power</td></tr>
+<tr><td><code>!</code></td><td>factorial</td></tr>
+<tr><td><code>!!</code></td><td>double factorial</td></tr>
 </table>
 
 <p>For example:</p>
@@ -387,7 +389,7 @@ <h3>Fixed input precision</h3>
 
 <p>Bug reports, questions and comments should be sent to <a href="mailto:Mikko.Tommila@apfloat.org">the author</a>.</p>
 
-<p>Last updated: April 9th, 2024</p>
+<p>Last updated: April 10th, 2024</p>
 
 </div>