more cleanup of mersenne-twister -- you can actually understand it now :)

extra/random/mersenne-twister/mersenne-twister.factor

@@ -2,9 +2,9 @@
 ! See http://factorcode.org/license.txt for BSD license.
 ! mersenne twister based on 
 ! http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/CODES/mt19937ar.c
-
 USING: arrays kernel math namespaces sequences system init
-accessors math.ranges random circular math.bitfields.lib ;
+accessors math.ranges random circular math.bitfields.lib
+combinators ;
 IN: random.mersenne-twister
 
 <PRIVATE
@@ -14,36 +14,37 @@ TUPLE: mersenne-twister seq i ;
 : mt-n 624 ; inline
 : mt-m 397 ; inline
 : mt-a HEX: 9908b0df ; inline
-: mt-hi HEX: 80000000 bitand ; inline
-: mt-lo HEX: 7fffffff bitand ; inline
-
-: set-generated ( y from-elt to seq -- )
-    >r >r >r [ 2/ ] [ odd? mt-a 0 ? ] bi
-    r> bitxor bitxor r> r> set-nth ; inline
 
 : calculate-y ( y1 y2 mt -- y )
-    tuck [ nth mt-hi ] [ nth mt-lo ] 2bi* bitor ; inline
+    tuck
+    [ nth 32 mask-bit ]
+    [ nth 31 bits ] 2bi* bitor ; inline
 
-: (mt-generate) ( n mt-seq -- y to from-elt )
-    [ >r dup 1+ r> calculate-y ]
-    [ >r mt-m + r> nth ]
-    [ drop ] 2tri ;
+: (mt-generate) ( n mt-seq -- next-mt )
+    [
+        [ dup 1+ ] [ calculate-y ] bi*
+        [ 2/ ] [ odd? mt-a 0 ? ] bi bitxor
+    ] [
+        [ mt-m + ] [ nth ] bi*
+    ] 2bi bitxor ;
 
 : mt-generate ( mt -- )
-    [ >r mt-n r> seq>> [ [ (mt-generate) ] keep set-generated ] curry each ]
-    [ 0 >>i drop ] bi ;
+    [
+        mt-n swap seq>> [
+            [ (mt-generate) ] [ set-nth ] 2bi
+        ] curry each
+    ] [ 0 >>i drop ] bi ;
 
-: init-mt-formula ( seq i -- f(seq[i]) )
-    tuck swap nth dup -30 shift bitxor 1812433253 * +
-    1+ 32-bit ;
+: init-mt-formula ( i seq -- f(seq[i]) )
+    dupd nth dup -30 shift bitxor 1812433253 * + 1+ 32 bits ;
 
 : init-mt-rest ( seq -- )
-    mt-n 1- [
-        dupd [ init-mt-formula ] keep 1+ rot set-nth
-    ] with each ;
+    mt-n 1- swap [
+        [ init-mt-formula ] [ >r 1+ r> set-nth ] 2bi
+    ] curry each ;
 
 : init-mt-seq ( seed -- seq )
-    32-bit mt-n 0 <array> <circular>
+    32 bits mt-n 0 <array> <circular>
     [ set-first ] [ init-mt-rest ] [ ] tri ;
 
 : mt-temper ( y -- yt )
@@ -52,6 +53,9 @@ TUPLE: mersenne-twister seq i ;
     dup 15 shift HEX: efc60000 bitand bitxor
     dup -18 shift bitxor ; inline
 
+: next-index  ( mt -- i )
+    dup i>> dup mt-n < [ nip ] [ drop mt-generate 0 ] if ;
+
 PRIVATE>
 
 : <mersenne-twister> ( seed -- obj )
@@ -62,7 +66,6 @@ M: mersenne-twister seed-random ( mt seed -- )
     init-mt-seq >>seq drop ;
 
 M: mersenne-twister random-32* ( mt -- r )
-    dup [ i>> ] [ seq>> ] bi
-    over mt-n < [ nip >r dup mt-generate 0 r> ] unless
-    nth mt-temper
-    swap [ 1+ ] change-i drop ;
+    [ next-index ]
+    [ seq>> nth mt-temper ]
+    [ [ 1+ ] change-i drop ] tri ;