Generalize factor-2s to eliminate special case exception

extra/math/miller-rabin/miller-rabin.factor

@@ -26,10 +26,8 @@ TUPLE: positive-even-expected n ;
     dup even? [ -1 shift >r 1+ r> (factor-2s) ] when ;
 
 : factor-2s ( n -- r s )
-    #! factor an even number into s * 2 ^ r
-    dup even? over 0 > and [
-        positive-even-expected construct-boa throw
-    ] unless 0 swap (factor-2s) ;
+    #! factor an integer into s * 2^r
+    0 swap (factor-2s) ;
 
 :: (miller-rabin) | n prime?! |
     n 1- factor-2s s set r set

extra/project-euler/common/common.factor

@@ -34,9 +34,6 @@ IN: project-euler.common
 : propagate ( bottom top -- newtop )
     [ over 1 tail rot first2 max rot + ] map nip ;
 
-: reduce-2s ( n -- r s )
-    dup even? [ factor-2s >r 1+ r> ] [ 1 swap ] if ;
-
 : shift-3rd ( seq obj obj -- seq obj obj )
     rot 1 tail -rot ;
 
@@ -92,7 +89,7 @@ PRIVATE>
 
 ! Optimized brute-force, is often faster than prime factorization
 : tau* ( m -- n )
-    reduce-2s [ perfect-square? -1 0 ? ] keep
+    factor-2s [ 1+ ] dip [ perfect-square? -1 0 ? ] keep
     dup sqrt >fixnum [1,b] [
-        dupd mod zero? [ >r 2 + r> ] when
+        dupd mod zero? [ [ 2 + ] dip ] when
     ] each drop * ;