Make bitsPerSubkey platform-dependent

Author: sjakobi

Data/HashMap/Internal.hs

@@ -1558,12 +1558,6 @@ submapBitmapIndexed comp !b1 !ary1 !b2 !ary2 = subsetBitmaps && go 0 0 (b1Orb2 .
     go !i !j !m
       | m > b1Orb2 = True
 
-#if WORD_SIZE_IN_BITS == 32
-      -- m can overflow to 0 on 32-bit platforms.
-      -- See #491.
-      | m == 0 = True
-#endif
-
       -- In case a key is both in ary1 and ary2, check ary1[i] <= ary2[j] and
       -- increment the indices i and j.
       | b1Andb2 .&. m /= 0 = comp (A.index ary1 i) (A.index ary2 j) &&
@@ -2449,7 +2443,11 @@ clone ary =
 --
 -- This constant is named /t/ in the original /Ideal Hash Trees/ paper.
 bitsPerSubkey :: Int
+#if WORD_SIZE_IN_BITS < 64
+bitsPerSubkey = 4
+#else
 bitsPerSubkey = 5
+#endif
 
 -- | The size of a 'Full' node, i.e. @2 ^ 'bitsPerSubkey'@.
 maxChildren :: Int