Add parameters procs from spec

ethash.nimble

@@ -7,4 +7,4 @@ srcDir        = "src"
 
 ### Dependencies
 
-requires "nim >= 0.17.2"
+requires "nim >= 0.17.2", "number_theory"

spec/ethash.py

@@ -48,8 +48,8 @@ def xor(a, b):
 
 def isprime(x):
     for i in range(2, int(x**0.5)):
-         if x % i == 0:
-             return False
+        if x % i == 0:
+            return False
     return True
 
 # ###############################################################################

src/ethash.nim

@@ -1,3 +1,50 @@
 # Copyright (c) 2018 Status Research & Development GmbH
 # Distributed under the Apache v2 License (license terms are at http://www.apache.org/licenses/LICENSE-2.0).
 
+import  math, number_theory # https://github.com/numforge/number-theory
+
+import  ./private/primes
+
+# TODO: consider switching from default int to uint64
+# Note: array/seq indexing requires an Ordinal, uint64 are not.
+# So to index arrays/seq we would need to cast uint64 to int anyway ...
+
+# ###############################################################################
+# Definitions
+
+const
+  WORD_BYTES = 4                    # bytes in word
+  DATASET_BYTES_INIT = 2^30         # bytes in dataset at genesis
+  DATASET_BYTES_GROWTH = 2^23       # dataset growth per epoch
+  CACHE_BYTES_INIT = 2^24           # bytes in cache at genesis
+  CACHE_BYTES_GROWTH = 2^17         # cache growth per epoch
+  CACHE_MULTIPLIER=1024             # Size of the DAG relative to the cache
+  EPOCH_LENGTH = 30000              # blocks per epoch
+  MIX_BYTES = 128                   # width of mix
+  HASH_BYTES = 64                   # hash length in bytes
+  DATASET_PARENTS = 256             # number of parents of each dataset element
+  CACHE_ROUNDS = 3                  # number of rounds in cache production
+  ACCESSES = 64                     # number of accesses in hashimoto loop
+
+# ###############################################################################
+# Parameters
+
+proc get_cache_size(block_number: Natural): int {.noSideEffect.}=
+  result = CACHE_BYTES_INIT + CACHE_BYTES_GROWTH * (block_number div EPOCH_LENGTH)
+  result -= HASH_BYTES
+  while (let dm = divmod(result, HASH_BYTES);
+          dm.rem == 0 and dm.quot.isPrime):
+        # In a static lang, checking that the result of a division is prime
+        # Means checking that reminder == 0 and quotient is prime
+    result -= 2 * HASH_BYTES
+
+proc get_full_size(block_number: Natural): int {.noSideEffect.}=
+  result = DATASET_BYTES_INIT + DATASET_BYTES_GROWTH * (block_number div EPOCH_LENGTH)
+  result -= MIX_BYTES
+  while (let dm = divmod(result, MIX_BYTES);
+          dm.rem == 0 and dm.quot.isPrime):
+    result -= 2 * MIX_BYTES
+
+
+when isMainModule:
+  echo get_full_size(100000)

src/private/primes.nim

@@ -0,0 +1,20 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the Apache v2 License (license terms are at http://www.apache.org/licenses/LICENSE-2.0).
+
+# Primality testing. TODO: a scalable implementation (i.e. Miller-Rabin)
+# See https://github.com/mratsim/nim-projecteuler/blob/master/src/lib/primes.nim
+
+import number_theory # https://github.com/numforge/number-theory
+
+
+proc isPrime*(x: SomeUnsignedInt): bool {.noSideEffect.}=
+  for i in 2 .. isqrt x:
+    if x mod i == 0:
+      return false
+  return true
+
+proc isPrime*(x: Natural): bool {.noSideEffect.}=
+  for i in 2 .. isqrt x:
+    if x mod i == 0:
+      return false
+  return true