commit 20b4ee407956441cca986cd41a4d3a362dfd9a49
Author: Balazs Komuves <bkomuves@gmail.com>
Date:   Fri Jul 28 22:10:14 2023 +0200

    quick Nim implementation of Poseidon2 via constantine (BN254, t=3)

diff --git a/hashes/Poseidon2/Nim/README.md b/hashes/Poseidon2/Nim/README.md
new file mode 100644
index 0000000..a76ddca
--- /dev/null
+++ b/hashes/Poseidon2/Nim/README.md
@@ -0,0 +1,8 @@
+
+Nim implementation of Poseidon2
+-------------------------------
+
+This one uses the constantine library, and is specialized to BN254 and t=3.
+
+Note: this is a learning exercise, I don't speak Nim...
+
diff --git a/hashes/Poseidon2/Nim/posei2.nim b/hashes/Poseidon2/Nim/posei2.nim
new file mode 100644
index 0000000..6d14313
--- /dev/null
+++ b/hashes/Poseidon2/Nim/posei2.nim
@@ -0,0 +1,106 @@
+
+# import std/sugar
+
+import 
+  ../constantine/constantine/math/arithmetic,
+  ../constantine/constantine/math/io/io_fields,
+  ../constantine/constantine/math/config/curves
+
+import types
+import roundconst
+
+#-------------------------------------------------------------------------------
+
+let zero : F = getZero()
+
+let external_round_const : array[24, F] = arrayFromHex( external_round_const_str )
+let internal_round_const : array[56, F] = arrayFromHex( internal_round_const_str )
+
+#-------------------------------------------------------------------------------
+
+# inplace sbox, x => x^5
+proc sbox(x: var F) : void =
+  var y = x
+  square(y)
+  square(y)
+  x *= y
+
+proc linear_layer(x, y, z : var F) =
+  var s = x ; s += y ; s += z
+  x += s
+  y += s
+  z += s
+
+proc internal_round(j: int; x, y, z: var F) =
+  x += internal_round_const[j]
+  sbox(x)
+  var s = x ; s += y ;  s += z
+  double(z)
+  x += s 
+  y += s
+  z += s
+
+proc external_round(j: int; x, y, z : var F) =
+  x += external_round_const[3*j+0]
+  y += external_round_const[3*j+1]
+  z += external_round_const[3*j+2]
+  sbox(x) ; sbox(y) ; sbox(z)
+  var s = x ; s += y ; s += z
+  x += s
+  y += s
+  z += s
+
+proc perm_inplace*(x, y, z : var F) =
+  linear_layer(x, y, z);
+  for j in 0..3:
+    external_round(j, x, y, z)
+  for j in 0..55:
+    internal_round(j, x, y, z)
+  for j in 4..7:
+    external_round(j, x, y, z)
+
+proc perm*(xyz: S) : S =
+  var (x,y,z) = xyz
+  perm_inplace(x, y, z)
+  return (x,y,z)
+
+#-------------------------------------------------------------------------------
+
+proc compress*(a, b : F) : F =
+  var x = a
+  var y = b
+  var z : F ; setZero(z)
+  perm_inplace(x, y, z)
+  return x
+
+proc merkle_root*(xs: openArray[F]) : F = 
+  let a = low(xs)
+  let b = high(xs)
+  let m = b-a+1
+
+  if m==1:
+    return xs[a]
+
+  else:
+    let halfn  : int  = m div 2
+    let n      : int  = 2*halfn
+    let is_odd : bool = (n != m)
+  
+    var ys : seq[F] = newSeq[F](halfn)
+
+    if not is_odd:
+      for i in 0..<halfn:
+        ys[i] = compress( xs[a+2*i], xs[a+2*i+1] )
+
+    else:
+      for i in 0..<halfn-1:
+        ys[i] = compress( xs[a+2*i], xs[a+2*i+1] )
+      # and the last one:
+      ys[halfn-1] = compress( xs[a+n-2], zero )
+
+    return merkle_root(ys)
+
+#-------------------------------------------------------------------------------
+  
+
+
diff --git a/hashes/Poseidon2/Nim/roundconst.nim b/hashes/Poseidon2/Nim/roundconst.nim
new file mode 100644
index 0000000..0b07b4d
--- /dev/null
+++ b/hashes/Poseidon2/Nim/roundconst.nim
@@ -0,0 +1,100 @@
+
+
+#-------------------------------------------------------------------------------
+
+let external_round_const_str* : array[24, string] =
+  [ "0x2c4c51fd1bb9567c27e99f5712b49e0574178b41b6f0a476cddc41d242cf2b43" ,
+    "0x1c5f8d18acb9c61ec6fcbfcda5356f1b3fdee7dc22c99a5b73a2750e5b054104" ,
+    "0x2d3c1988b4541e4c045595b8d574e98a7c2820314a82e67a4e380f1c4541ba90" ,
+  #
+    "0x052547dc9e6d936cab6680372f1734c39f490d0cb970e2077c82f7e4172943d3" ,
+    "0x29d967f4002adcbb5a6037d644d36db91f591b088f69d9b4257694f5f9456bc2" ,
+    "0x0350084b8305b91c426c25aeeecafc83fc5feec44b9636cb3b17d2121ec5b88a" ,
+  #
+    "0x1815d1e52a8196127530cc1e79f07a0ccd815fb5d94d070631f89f6c724d4cbe" ,
+    "0x17b5ba882530af5d70466e2b434b0ccb15b7a8c0138d64455281e7724a066272" ,
+    "0x1c859b60226b443767b73cd1b08823620de310bc49ea48662626014cea449aee" ,
+  #
+    "0x1b26e7f0ac7dd8b64c2f7a1904c958bb48d2635478a90d926f5ff2364effab37" ,
+    "0x2da7f36850e6c377bdcdd380efd9e7c419555d3062b0997952dfbe5c54b1a22e" ,
+    "0x17803c56450e74bc6c7ff97275390c017f682db11f3f4ca6e1f714efdfb9bd66" ,
+  #
+    "0x25672a14b5d085e31a30a7e1d5675ebfab034fb04dc2ec5e544887523f98dede" ,
+    "0x0cf702434b891e1b2f1d71883506d68cdb1be36fa125674a3019647b3a98accd" ,
+    "0x1837e75235ff5d112a5eddf7a4939448748339e7b5f2de683cf0c0ae98bdfbb3" ,
+  #
+    "0x1cd8a14cff3a61f04197a083c6485581a7d836941f6832704837a24b2d15613a" ,
+    "0x266f6d85be0cef2ece525ba6a54b647ff789785069882772e6cac8131eecc1e4" ,
+    "0x0538fde2183c3f5833ecd9e07edf30fe977d28dd6f246d7960889d9928b506b3" ,
+  #
+    "0x07a0693ff41476abb4664f3442596aa8399fdccf245d65882fce9a37c268aa04" ,
+    "0x11eb49b07d33de2bd60ea68e7f652beda15644ed7855ee5a45763b576d216e8e" ,
+    "0x08f8887da6ce51a8c06041f64e22697895f34bacb8c0a39ec12bf597f7c67cfc" ,
+  #  
+    "0x2a912ec610191eb7662f86a52cc64c0122bd5ba762e1db8da79b5949fdd38092" ,
+    "0x2031d7fd91b80857aa1fef64e23cfad9a9ba8fe8c8d09de92b1edb592a44c290" ,
+    "0x0f81ebce43c47711751fa64d6c007221016d485641c28c507d04fd3dc7fba1d2" ,
+  ]
+
+#-------------------------------------------------------------------------------
+
+let internal_round_const_str* : array[56, string] =
+  [ "0x15ce7e5ae220e8623a40b3a3b22d441eff0c9be1ae1d32f1b777af84eea7e38c" ,
+    "0x1bf60ac8bfff0f631983c93e218ca0d4a4059c254b4299b1d9984a07edccfaf0" ,
+    "0x0fab0c9387cb2bec9dc11b2951088b9e1e1d2978542fc131f74a8f8fdac95b40" ,
+    "0x07d085a48750738019784663bccd460656dc62c1b18964a0d27a5bd0c27ee453" ,
+    "0x10d57b1fad99da9d3fe16cf7f5dae05be844f67b2e7db3472a2e96e167578bc4" ,
+    "0x0c36c40f7bd1934b7d5525031467aa39aeaea461996a70eda5a2a704e1733bb0" ,
+    "0x0e4b65a0f3e1f9d3166a2145063c999bd08a4679676d765f4d11f97ed5c080ae" ,
+    "0x1ce5561061120d5c7ea09da2528c4c041b9ad0f05d655f38b10d79878b69f29d" ,
+    "0x2d323f651c3da8f0e0754391a10fa111b25dfa00471edf5493c44dfc3f28add6" ,
+    "0x05a0741ee5bdc3e099fd6bdad9a0865bc9ceecd13ea4e702e536dd370b8f1953" ,
+    "0x176a2ec4746fc0e0eca9e5e11d6facaee05524a92e5785c8b8161780a4435136" ,
+    "0x0691faf0f42a9ed97629b1ae0dc7f1b019c06dd852cb6efe57f7eeb1aa865aef" ,
+    "0x0e46cf138dad09d61b9a7cab95a23b5c8cb276874f3715598bacb55d5ad271de" ,
+    "0x0f18c3d95bac1ac424160d240cdffc2c44f7b6315ba65ed3ff2eff5b3e48b4f2" ,
+    "0x2eea6af14b592ec45a4119ac1e6e6f0312ecd090a096e340d472283e543ddff7" ,
+    "0x06b0d7a8f4ce97d049ae994139f5f71dca4899d4f1cd3dd83a32a89a58c0a8e6" ,
+    "0x019df0b9828eed5892dd55c1ad6408196f6293d600ef4491703a1b37e119ba8e" ,
+    "0x08ca5e3c93817cdb1c2b2a12d02c779d74c1bb12b6668f3ab3ddd7837f3a4a00" ,
+    "0x28382d747e3fd6cb2e0d8e8edd79c5313eed307a3517c11046245b1476e4f701" ,
+    "0x0ca89aecd5675b77c8271765da98cfcb6875b3053d4742c9ff502861bd16ad28" ,
+    "0x19046bc0b03ca90802ec83f212001e7ffd7f9224cfffae523451deb52eab3787" ,
+    "0x036fd7dfa1c05110b3428e6abcc43e1de9abba915320c4a600f843bfb676ca51" ,
+    "0x08f0a7abcb1a2f6595a9b7380c5028e3999db4fe5cb21892e5bb5cb11a7757ba" ,
+    "0x0b614acc1ce3fbe9048f8385e4ee24c3843deea186bacea3c904c9f6340ad8cb" ,
+    "0x00b2d98c5d988f9b41f2c98e017fc954a6ae423b2261575941f8eac8835d985c" ,
+    "0x1457f18555b7973ba5b311d57ec5d77e936980b97f5973875f1f7cc765a4fc95" ,
+    "0x002b453debc1bee525cb751bc10641a6b86f847d696418cf1144950982591bfa" ,
+    "0x0c2af1abcc6ece77218315d2af445ccbfc6647b7af2510682882cc792c6bb8cf" ,
+    "0x0e2825d9eb84b59902a1adb49ac0c2c291dee7c45d2e8c30369a4d595039e8ad" ,
+    "0x297e2e86a8c672d39f3343b8dfce7a6f20f3571bfd5c8a28e3905aa2dcfeca44" ,
+    "0x00d397281d902e49ec6504ba9186e806db9ad4fc8f86e7277aa7f1467eb6f9de" ,
+    "0x2fb7c89c372d7e2050e7377ed471000c73544a2b9fd66557f3577c09cac98b4b" ,
+    "0x16125247be4387a8c3e62490167f0cffdba02eda4f018d0b40639a13bb0cfef9" ,
+    "0x2291fd9d442f2d9b97ab22f7d4d52c2a82e41f852cf620b144612650a39e26e8" ,
+    "0x1eec61f16a275ae238540feaeeadfec56d32171b1cc393729d06f37f476fde71" ,
+    "0x259ce871ba5dacbb48d8aed3d8513eef51558dc0b360f28c1a15dbfc5e7f6ca2" ,
+    "0x2d3376a14ddbf95587e2f7567ff04fe13a3c7cb17363c8b9c5dd1d9262a210cb" ,
+    "0x13b843d9f65f4cddd7ce10d9cad9b8b99ac5e9a8c4269288173a91c0f3c3b084" ,
+    "0x0b52e9b2f1aa9fd204e4a42c481cc76c704783e34114b8e93e026a50fa9764e8" ,
+    "0x1fd083229276c7f27d3ad941476b394ff37bd44d3a1e9caca1400d9077a2056c" ,
+    "0x22743c328a6283f3ba7379af22c684c498568fd7ad9fad5151368c913197cbd9" ,
+    "0x043007aefd9741070d95caaaba0c1b070e4eec8eef8c1e512c8e579c6ed64f76" ,
+    "0x17ab175144f64bc843074f6b3a0c57c5dd2c954af8723c029ee642539496a7b3" ,
+    "0x2befcad3d53fba5eeef8cae9668fed5c1e9e596a46e8458e218f7a665fddf4eb" ,
+    "0x15151c4116d97de74bfa6ca3178f73c8fe8fe612c70c6f85a7a1551942cb71cc" ,
+    "0x2ac40bf6c3176300a6835d5fc7cc4fd5e5d299fb1baa86487268ec1b9eedfa97" ,
+    "0x0f151de1f01b4e24ffe04279318f0a68efabb485188f191e37e6915ff6059f6e" ,
+    "0x2e43dffc34537535182aebac1ad7bf0a5533b88f65f9652f0ad584e2ffc4dd1f" ,
+    "0x2ebabc2c37ef53d8b13b24a2a2b729d536735f58956125a3876da0664c2442d7" ,
+    "0x0dc3beceb34e49f5ad7226dd202c5cf879dffcc9a6dd32a300e8f2a4b59edf03" ,
+    "0x2f1ddeccce83adf68779c53b639871a8f81d4d00aefe1e812efce8ec999d457d" ,
+    "0x1f63e41280ff5c021715d52b19780298ed8bd3d5eb506316b527e24149d4d4f1" ,
+    "0x1b8c1252a5888f8cb2672effb5df49c633d3fd7183271488a1c40d0f88e7636e" ,
+    "0x0f45697130f5498e2940568ef0d5e9e16b1095a6cdbb6411df20a973c605e70b" ,
+    "0x0780ccc403cdd68983acbd34cda41cacfb2cf911a93076bc25587b4b0aed4929" ,
+    "0x238d26ca97c691591e929f32199a643550f325f23a85d420080b289d7cecc9d4" 
+  ]
+
+#-------------------------------------------------------------------------------
\ No newline at end of file
diff --git a/hashes/Poseidon2/Nim/test.nim b/hashes/Poseidon2/Nim/test.nim
new file mode 100644
index 0000000..58a6214
--- /dev/null
+++ b/hashes/Poseidon2/Nim/test.nim
@@ -0,0 +1,34 @@
+
+import std/math
+
+import ../constantine/constantine/math/io/io_fields
+import ../constantine/constantine/math/config/curves
+
+import types
+import posei2
+
+#-------------------------------------------------------------------------------
+
+var x: F = toF(0)
+var y: F = toF(1)
+var z: F = toF(2)
+
+perm_inplace(x, y, z)
+
+echo "\npermutation of (0,1,2):"
+echo( toDecimal(x) )
+echo( toDecimal(y) )
+echo( toDecimal(z) )
+
+#---------------------------------------
+
+let m = 17
+let n = 2^m
+var xs: seq[F]
+for i in 1..n:
+  xs.add( toF(i) )
+
+echo("\nmerkle root of ",1,"..",n,":")
+let root = merkle_root(xs)
+echo( toHex(root) )
+
diff --git a/hashes/Poseidon2/Nim/types.nim b/hashes/Poseidon2/Nim/types.nim
new file mode 100644
index 0000000..3d32508
--- /dev/null
+++ b/hashes/Poseidon2/Nim/types.nim
@@ -0,0 +1,36 @@
+
+import 
+  ../constantine/constantine/math/io/io_fields,
+  ../constantine/constantine/math/arithmetic,
+  ../constantine/constantine/math/config/curves
+
+#-------------------------------------------------------------------------------
+
+type B* = BigInt[254]
+type F* = Fr[BN254_Snarks]
+type S* = (F,F,F)
+
+#-------------------------------------------------------------------------------
+
+func getZero*() : F =
+  var z : F
+  setZero(z)
+  return z
+
+func toF*(a: int) : F = 
+  var y : F
+  fromInt(y, a);
+  return y
+
+func hexToF*(s : string) : F = 
+  var y : F
+  fromHex(y, s)
+  return y
+
+func arrayFromHex*[N]( inp: array[N, string]) : array[N, F] = 
+  var tmp : array[N, F]
+  for i in low(inp)..high(inp):
+    tmp[i] = hexToF( inp[i] )
+  return tmp
+
+#-------------------------------------------------------------------------------