add toggle-bit word to math.bitwise

basis/math/bitwise/bitwise-docs.factor

@@ -204,8 +204,25 @@ HELP: on-bits
         "64 on-bits .h"
         "ffffffffffffffff"
     }
+} ;
+
+HELP: toggle-bit
+{ $values
+     { "m" integer }
+     { "n" integer }
+     { "m'" integer }
 }
-;
+{ $description "Toggles the nth bit of an integer." }
+{ $examples
+    { $example "USING: math.bitwise kernel prettyprint ;"
+        "0 3 toggle-bit .b"
+        "1000"
+    }
+    { $example "USING: math.bitwise kernel prettyprint ;"
+        "BIN: 1000 3 toggle-bit .b"
+        "0"
+    }
+} ;
 
 HELP: set-bit
 { $values

basis/math/bitwise/bitwise-tests.factor

@@ -29,3 +29,6 @@ IN: math.bitwise.tests
 \ foo must-infer
 
 [ 1 ] [ { 1 } flags ] unit-test
+
+[ 8 ] [ 0 3 toggle-bit ] unit-test
+[ 0 ] [ 8 3 toggle-bit ] unit-test

basis/math/bitwise/bitwise.factor

@@ -17,6 +17,7 @@ IN: math.bitwise
 : bits ( m n -- m' ) 2^ wrap ; inline
 : mask-bit ( m n -- m' ) 2^ mask ; inline
 : on-bits ( n -- m ) 2^ 1- ; inline
+: toggle-bit ( m n -- m' ) 2^ bitxor ; inline
 
 : shift-mod ( n s w -- n )
     [ shift ] dip 2^ wrap ; inline