WIP: Improve bit-twiddling

Author: jakobnissen

src/bit-manipulation/bit-manipulation.jl

@@ -43,9 +43,7 @@ end
 
 @inline function gc_bitcount(x::Unsigned, ::NucleicAcidAlphabet{2})
     msk = repeatpattern(typeof(x), 0x55)
-    c = x & msk
-    g = (x >> 1) & msk
-    return count_ones(c ⊻ g)
+    return count_ones((x ⊻ (x >>> 1)) & msk)
 end
 
 @inline function gc_bitcount(x::Unsigned, ::NucleicAcidAlphabet{4})