diff --git a/poseidon2.nim b/poseidon2.nim
index 261879b..44b8e58 100644
--- a/poseidon2.nim
+++ b/poseidon2.nim
@@ -1,55 +1,15 @@
-import
-  constantine/math/arithmetic,
-  constantine/math/config/curves
+import constantine/math/arithmetic
 
 import poseidon2/types
-import poseidon2/roundconst
+import poseidon2/roundfun
 import poseidon2/io
 
 export toBytes
 
 #-------------------------------------------------------------------------------
 
-const zero : F = getZero()
-
-const externalRoundConst : array[24, F] = arrayFromHex( externalRoundConstStr )
-const internalRoundConst : array[56, F] = arrayFromHex( internalRoundConstStr )
-
-#-------------------------------------------------------------------------------
-
-# inplace sbox, x => x^5
-func sbox(x: var F) : void =
-  var y = x
-  square(y)
-  square(y)
-  x *= y
-
-func linearLayer(x, y, z : var F) =
-  var s = x ; s += y ; s += z
-  x += s
-  y += s
-  z += s
-
-func internalRound(j: int; x, y, z: var F) =
-  x += internalRoundConst[j]
-  sbox(x)
-  var s = x ; s += y ;  s += z
-  double(z)
-  x += s
-  y += s
-  z += s
-
-func externalRound(j: int; x, y, z : var F) =
-  x += externalRoundConst[3*j+0]
-  y += externalRoundConst[3*j+1]
-  z += externalRoundConst[3*j+2]
-  sbox(x) ; sbox(y) ; sbox(z)
-  var s = x ; s += y ; s += z
-  x += s
-  y += s
-  z += s
-
-func permInplace*(x, y, z : var F) =
+# the Poseidon2 permutation (mutable, in-place version)
+proc permInplace*(x, y, z : var F) =
   linearLayer(x, y, z);
   for j in 0..3:
     externalRound(j, x, y, z)
@@ -58,6 +18,7 @@ func permInplace*(x, y, z : var F) =
   for j in 4..7:
     externalRound(j, x, y, z)
 
+# the Poseidon2 permutation
 func perm*(xyz: S) : S =
   var (x,y,z) = xyz
   permInplace(x, y, z)
@@ -65,6 +26,56 @@ func perm*(xyz: S) : S =
 
 #-------------------------------------------------------------------------------
 
+# sponge with rate=1 (capacity=2) 
+func spongeWithRate1*(xs: openArray[F]) : F =
+  let a = low(xs)
+  let b = high(xs)
+  let n = b-a+1
+
+  var s0 : F = zero
+  var s1 : F = zero
+  var s2 : F = zero
+
+  for i in 0..<n:
+    s0 += xs[a+i]
+    permInplace(s0,s1,s2)
+
+  # padding
+  s0 += one;
+  permInplace(s0,s1,s2)
+  return s0
+
+# sponge with rate=2 (capacity=1) 
+func spongeWithRate2*(xs: openArray[F]) : F =
+  let a = low(xs)
+  let b = high(xs)
+  let n = b-a+1
+  let halfn  : int  = n div 2  
+
+  var s0 : F = zero
+  var s1 : F = zero
+  var s2 : F = zero
+
+  for i in 0..<halfn:
+    s0 += xs[a+2*i  ]
+    s1 += xs[a+2*i+1]
+    permInplace(s0,s1,s2)
+
+  if (2*halfn == n):
+    # padding even input
+    s0 += one
+    s1 += zero
+  else:
+    # padding odd input
+    s0 += xs[b]
+    s1 += one
+
+  permInplace(s0,s1,s2) 
+  return s0
+
+#-------------------------------------------------------------------------------
+
+# 2-to-1 compression
 func compress*(a, b : F) : F =
   var x = a
   var y = b
@@ -101,3 +112,5 @@ func merkleRoot*(xs: openArray[F]) : F =
 
 func merkleRoot*(bytes: openArray[byte]): F =
   merkleRoot(seq[F].fromBytes(bytes))
+
+#-------------------------------------------------------------------------------
diff --git a/poseidon2/roundfun.nim b/poseidon2/roundfun.nim
new file mode 100644
index 0000000..8b11f16
--- /dev/null
+++ b/poseidon2/roundfun.nim
@@ -0,0 +1,51 @@
+import
+  constantine/math/arithmetic,
+  constantine/math/config/curves
+
+import ./types
+import ./roundconst
+
+#-------------------------------------------------------------------------------
+
+const zero* : F = getZero()
+const one*  : F = getOne()
+
+const externalRoundConst : array[24, F] = arrayFromHex( externalRoundConstStr )
+const internalRoundConst : array[56, F] = arrayFromHex( internalRoundConstStr )
+
+#-------------------------------------------------------------------------------
+
+# inplace sbox, x => x^5
+func sbox*(x: var F) : void =
+  var y = x
+  square(y)
+  square(y)
+  x *= y
+
+func linearLayer*(x, y, z : var F) =
+  var s = x ; s += y ; s += z
+  x += s
+  y += s
+  z += s
+
+func internalRound*(j: int; x, y, z: var F) =
+  x += internalRoundConst[j]
+  sbox(x)
+  var s = x ; s += y ;  s += z
+  double(z)
+  x += s
+  y += s
+  z += s
+
+func externalRound*(j: int; x, y, z : var F) =
+  x += externalRoundConst[3*j+0]
+  y += externalRoundConst[3*j+1]
+  z += externalRoundConst[3*j+2]
+  sbox(x) ; sbox(y) ; sbox(z)
+  var s = x ; s += y ; s += z
+  x += s
+  y += s
+  z += s
+
+#-------------------------------------------------------------------------------
+
diff --git a/poseidon2/types.nim b/poseidon2/types.nim
index a14d541..093a909 100644
--- a/poseidon2/types.nim
+++ b/poseidon2/types.nim
@@ -1,8 +1,8 @@
 
 import
+  constantine/math/arithmetic,
   constantine/math/io/io_fields,
   constantine/math/io/io_bigints,
-  constantine/math/arithmetic,
   constantine/math/config/curves
 
 #-------------------------------------------------------------------------------
@@ -18,9 +18,17 @@ func getZero*() : F =
   setZero(z)
   return z
 
+func getOne*() : F = 
+  var y : F
+  # y.fromUint(1'u32)       # WTF, why does this not compile ???
+  y.fromHex("0x01")
+  return y
+
+# for some reason this one does not compile... ???
+# (when actually called)
 func toF*(a: int) : F =
   var y : F
-  fromInt(y, a);
+  y.fromInt(a)
   return y
 
 func hexToF*(s : string, endian: static Endianness = bigEndian) : F =
diff --git a/tests/poseidon2/testPoseidon2.nim b/tests/poseidon2/testPoseidon2.nim
index 70e6ea4..f28ef20 100644
--- a/tests/poseidon2/testPoseidon2.nim
+++ b/tests/poseidon2/testPoseidon2.nim
@@ -10,6 +10,36 @@ import constantine/serialization/codecs
 import poseidon2/types
 import poseidon2
 
+#-------------------------------------------------------------------------------
+
+const expectedSpongeResultsRate1 : array[8, string] = 
+  [ "12363515589665961836680709257448433057869762330741639517836048636244832188495"
+  , "10755250120808789043370150604836786069442045362641800439807384337872752972068"
+  , "04842014531366721455661330916203255410159059117951668762867230544004815370337"
+  , "13502515636936876459766686836354199651004594178376827739246669803080321705927"
+  , "19312121576697000598919845239663673946550934099828684806027699882665482322097"
+  , "21509595983900483103260021285060939918324350560398732346653142062765920502059"
+  , "11892726572958426459775026381831352388154613015696290329810000571844227402585"
+  , "10284126944232604349630438079200913190801781418325975675236599364113149409058"
+  ]
+
+# TODO: add domain separation between rate=1 and rate=2, so that the empty input
+# gives different results. But this has to be done in all the other Poseidon2 libraries
+# too (circom, Haskell, C...)
+
+const expectedSpongeResultsRate2 : array[8, string] = 
+  [ "12363515589665961836680709257448433057869762330741639517836048636244832188495"
+  , "00899009032366875286186953183805404053380636995610127460025486428583509745414"
+  , "16500906802543951227422597869354004883060519121579073949799015758201044544012"
+  , "05275430613748165078459451567241807462288293965310307668712900802458919462965"
+  , "13763559248248167400098483085605230840597893317332127197498651878933380690961"
+  , "14871143128308815290845020646262475973102494373985615216162863857354721038367"
+  , "02746725081632011689597680224823496636241961292066939394613880404914874634920"
+  , "02290144245981244996669076598332792758523446545263085369617640761875376727694"
+  ]
+
+#-------------------------------------------------------------------------------
+
 suite "poseidon2":
 
   test "permutation in place":
@@ -23,6 +53,24 @@ suite "poseidon2":
     check toDecimal(y) == "09030699330013392132529464674294378792132780497765201297316864012141442630280"
     check toDecimal(z) == "09137931384593657624554037900714196568304064431583163402259937475584578975855"
 
+  test "sponge with rate=1":
+    for n in 0..7:
+      var xs: seq[F]
+      for i in 1..n:
+        xs.add( toF(i) )
+      let h = spongeWithRate1(xs)
+      # echo(toDecimal(h))
+      check toDecimal(h) == expectedSpongeResultsRate1[n] 
+
+  test "sponge with rate=2":
+    for n in 0..7:
+      var xs: seq[F]
+      for i in 1..n:
+        xs.add( toF(i) )
+      let h = spongeWithRate2(xs)
+      # echo(toDecimal(h))
+      check toDecimal(h) == expectedSpongeResultsRate2[n] 
+
   test "merkle root of field elements":
     let m = 17
     let n = 2^m