Pass the tests 🔥 ⚠⚠ Endianness in PoW spec seems wrong

src/ethash.nim

@@ -170,7 +170,11 @@ proc hashimoto(header: Hash[256],
   let s_words = cast[ptr array[16, uint32]](addr s) # Alias for to interpret s as an uint32 array
 
   s_bytes[0..<32] = header.toByteArrayBE            # We first populate the first 40 bytes of s with the concatenation
-  s_bytes[32..<40] = nonce.toByteArrayBE
+
+  when system.cpuEndian == littleEndian:            # ⚠⚠ Warning ⚠⚠, the spec is WRONG compared to tests here
+    s_bytes[32..<40] = cast[array[8,byte]](nonce)   # the nonce should be concatenated with its LITTLE ENDIAN representation
+  else:
+    raise newException(ValueError, "Big endian system not supported yet")
 
   s = keccak_512 s_bytes[0..<40]                    # TODO: Does this allocate a seq?
 
@@ -196,6 +200,7 @@ proc hashimoto(header: Hash[256],
   for i in countup(0, mix.len - 1, 4):
     cmix[i div 4] = mix[i].fnv(mix[i+1]).fnv(mix[i+2]).fnv(mix[i+3])
 
+  # ⚠⚠ Warning ⚠⚠: Another big endian little endian issue?
   # result.mix_digest = cast[Hash[256]](
   #   mapArray(cmix, x.toByteArrayBE) # Each uint32 must be changed to Big endian
   #   )

src/private/casting.nim

@@ -94,7 +94,7 @@ proc toHex*(ba: seq[byte]): string {.noSideEffect, noInit.}=
     result[2*i+1] = hexChars[int ba[i] and 0xF]
 
 proc toByteArrayBE*[T: SomeInteger](num: T): ByteArrayBE[T.sizeof] {.noSideEffect, noInit, inline.}=
-  ## Convert an UInt256 (in native host endianness) to a big-endian byte array
+  ## Convert an int (in native host endianness) to a big-endian byte array
   # Note: only works on devel
 
   when system.cpuEndian == bigEndian:

tests/all_tests.nim

@@ -166,12 +166,12 @@ suite "Dagger hashimoto computation":
 
     check: $calc_dataset_item(cache, 0) == expected
 
-  # test "Real dataset and recomputation from cache matches":
+  test "Real dataset and recomputation from cache matches":
-  #   # https://github.com/ethereum/ethash/blob/f5f0a8b1962544d2b6f40df8e4b0d9a32faf8f8e/test/c/test.cpp#L360-L374
+    # https://github.com/ethereum/ethash/blob/f5f0a8b1962544d2b6f40df8e4b0d9a32faf8f8e/test/c/test.cpp#L360-L374
-  #   for i in 0 ..< full_size div sizeof(Hash[512]):
+    for i in 0 ..< full_size div sizeof(Hash[512]):
-  #     for j in 0 ..< 32:
+      for j in 0 ..< 32:
-  #       let expected = calc_dataset_item(cache, j)
+        let expected = calc_dataset_item(cache, j)
-  #       check: full[j] == expected
+        check: full[j] == expected
 
   test "Light and full Hashimoto agree":
     # https://github.com/ethereum/ethash/blob/f5f0a8b1962544d2b6f40df8e4b0d9a32faf8f8e/test/python/test_pyethash.py#L44-L58