Move compress() into its own module

poseidon2.nim

@@ -5,22 +5,16 @@ import poseidon2/types
 import poseidon2/permutation
 import poseidon2/io
 import poseidon2/sponge
+import poseidon2/compress
 
 export sponge
+export compress
 export toBytes
 export elements
 export types
 
 #-------------------------------------------------------------------------------
 
-# 2-to-1 compression
-func compress*(a, b : F) : F =
-  var x = a
-  var y = b
-  var z : F ; setZero(z)
-  permInplace(x, y, z)
-  return x
-
 func merkleRoot*(xs: openArray[F]) : F =
   let a = low(xs)
   let b = high(xs)

poseidon2/compress.nim

@@ -0,0 +1,10 @@
+import ./types
+import ./permutation
+
+# 2-to-1 compression
+func compress*(a, b : F) : F =
+  var x = a
+  var y = b
+  var z : F = zero
+  permInplace(x, y, z)
+  return x