Merge pull request ethereum#883 from hskang9/patch-1

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Author: joeykrug

ethereum/pow/ethash.py

@@ -28,6 +28,7 @@ def _get_cache(seed, n):
     for i in range(1, n):
         o.append(sha3_512(o[-1]))
 
+    # Use a low-round version of randmemohash    
     for _ in range(CACHE_ROUNDS):
         for i in range(n):
             v = o[i][0] % n
@@ -39,9 +40,11 @@ def _get_cache(seed, n):
 def calc_dataset_item(cache, i):
     n = len(cache)
     r = HASH_BYTES // WORD_BYTES
+    # initialize the mix
     mix = copy.copy(cache[i % n])
     mix[0] ^= i
     mix = sha3_512(mix)
+    # fnv it with a lot of random cache nodes based on i
     for j in range(DATASET_PARENTS):
         cache_index = fnv(i ^ j, mix[j % r])
         mix = list(map(fnv, mix, cache[cache_index % n]))
@@ -64,16 +67,19 @@ def hashimoto(header, nonce, full_size, dataset_lookup):
     n = full_size // HASH_BYTES
     w = MIX_BYTES // WORD_BYTES
     mixhashes = MIX_BYTES // HASH_BYTES
+    # combine header+nonce into a 64 byte seed
     s = sha3_512(header + nonce[::-1])
     mix = []
     for _ in range(MIX_BYTES // HASH_BYTES):
         mix.extend(s)
+    # mix in random dataset nodes
     for i in range(ACCESSES):
         p = fnv(i ^ s[0], mix[i % w]) % (n // mixhashes) * mixhashes
         newdata = []
         for j in range(mixhashes):
             newdata.extend(dataset_lookup(p + j))
         mix = list(map(fnv, mix, newdata))
+    # compress mix
     cmix = []
     for i in range(0, len(mix), 4):
         cmix.append(fnv(fnv(fnv(mix[i], mix[i + 1]), mix[i + 2]), mix[i + 3]))