remove quadratic deposit Merkle tree initialization

AllTests-mainnet.md

@@ -237,7 +237,7 @@ OK: 5/5 Fail: 0/5 Skip: 0/5
 OK: 8/8 Fail: 0/8 Skip: 0/8
 ## chain DAG finalization tests [Preset: mainnet]
 ```diff
-+ prune heads on finalization [Preset: mainnet]                                              OK
++ init with gaps [Preset: mainnet]                                                           OK
 ```
 OK: 1/1 Fail: 0/1 Skip: 0/1
 ## hash

beacon_chain.nimble

@@ -72,7 +72,6 @@ task test, "Run all tests":
   # Consensus object SSZ tests
   buildAndRunBinary "test_fixture_ssz_consensus_objects", "tests/official/", "-d:chronicles_log_level=TRACE -d:const_preset=mainnet"
 
-  # 0.12.1
   buildAndRunBinary "all_fixtures_require_ssz", "tests/official/", "-d:chronicles_log_level=TRACE -d:const_preset=mainnet"
 
   # State and block sims; getting to 4th epoch triggers consensus checks

beacon_chain/merkle_minimal.nim

@@ -18,21 +18,15 @@ import
   ../../beacon_chain/spec/[beaconstate, datatypes, digest, helpers],
   ../../beacon_chain/ssz/merkleization
 
-# TODO
-#
-# This module currently represents a direct translation of the Python
-# code, appearing in the spec. We need to review it to ensure that it
-# doesn't duplicate any code defined in ssz.nim already.
-#
-# All tests need to be moved to the test suite.
+# TODO All tests need to be moved to the test suite.
 
-func round_step_down*(x: Natural, step: static Natural): int {.inline.} =
+func round_step_down(x: Natural, step: static Natural): int {.inline.} =
   ## Round the input to the previous multiple of "step"
   when (step and (step - 1)) == 0:
     # Step is a power of 2. (If compiler cannot prove that x>0 it does not make the optim)
-    result = x and not(step - 1)
+    x and not(step - 1)
   else:
-    result = x - x mod step
+    x - x mod step
 
 type SparseMerkleTree*[Depth: static int] = object
   ## Sparse Merkle tree
@@ -41,7 +35,7 @@ type SparseMerkleTree*[Depth: static int] = object
   # and the root hash at the last depth
   nnznodes: array[Depth+1, seq[Eth2Digest]]  # nodes that leads to non-zero leaves
 
-proc merkleTreeFromLeaves*(
+func merkleTreeFromLeaves(
         values: openarray[Eth2Digest],
         Depth: static[int] = DEPOSIT_CONTRACT_TREE_DEPTH
       ): SparseMerkleTree[Depth] =
@@ -68,21 +62,28 @@ proc merkleTreeFromLeaves*(
         h.update zeroHashes[depth-1]
       result.nnznodes[depth].add nodeHash
 
-proc getMerkleProof*[Depth: static int](tree: SparseMerkleTree[Depth],
-                                        index: int): array[Depth, Eth2Digest] =
-
+func getMerkleProof[Depth: static int](tree: SparseMerkleTree[Depth],
+                                       index: int,
+                                       depositMode = false): array[Depth, Eth2Digest] =
   # Descend down the tree according to the bit representation
   # of the index:
   #   - 0 --> go left
   #   - 1 --> go right
   let path = uint32(index)
+  var depthLen = index + 1
   for depth in 0 ..< Depth:
     let nodeIdx = int((path shr depth) xor 1)
-    if nodeIdx < tree.nnznodes[depth].len:
+
+    # depositMode simulates only having constructed SparseMerkleTree[Depth]
+    # through exactly deposit specified.
+    if nodeIdx < tree.nnznodes[depth].len and
+        (nodeIdx < depthLen or not depositMode):
       result[depth] = tree.nnznodes[depth][nodeIdx]
     else:
       result[depth] = zeroHashes[depth]
 
+    depthLen = (depthLen + 1) div 2
+
 func attachMerkleProofs*(deposits: var openarray[Deposit]) =
   let deposit_data_roots = mapIt(deposits, it.data.hash_tree_root)
   var
@@ -91,9 +92,9 @@ func attachMerkleProofs*(deposits: var openarray[Deposit]) =
       deposit_data_roots, 1'i64 shl DEPOSIT_CONTRACT_TREE_DEPTH):
     deposit_data_sums.add prefix_root
 
+  let merkle_tree = merkleTreeFromLeaves(deposit_data_roots)
   for val_idx in 0 ..< deposits.len:
-    let merkle_tree = merkleTreeFromLeaves(deposit_data_roots[0..val_idx])
-    deposits[val_idx].proof[0..31] = merkle_tree.getMerkleProof(val_idx)
+    deposits[val_idx].proof[0..31] = merkle_tree.getMerkleProof(val_idx, true)
     deposits[val_idx].proof[32].data[0..7] = uint_to_bytes8((val_idx + 1).uint64)
 
     doAssert is_valid_merkle_branch(

research/block_sim.nim

@@ -40,7 +40,7 @@ type Timers = enum
 
 # TODO confutils is an impenetrable black box. how can a help text be added here?
 cli do(slots = SLOTS_PER_EPOCH * 6,
-       validators = SLOTS_PER_EPOCH * 130, # One per shard is minimum
+       validators = SLOTS_PER_EPOCH * 200, # One per shard is minimum
        attesterRatio {.desc: "ratio of validators that attest in each round"} = 0.73,
        blockRatio {.desc: "ratio of slots with blocks"} = 1.0,
        replay = true):

research/state_sim.nim

@@ -34,7 +34,7 @@ proc writeJson*(fn, v: auto) =
   Json.saveFile(fn, v, pretty = true)
 
 cli do(slots = SLOTS_PER_EPOCH * 6,
-       validators = SLOTS_PER_EPOCH * 100, # One per shard is minimum
+       validators = SLOTS_PER_EPOCH * 200, # One per shard is minimum
        json_interval = SLOTS_PER_EPOCH,
        write_last_json = false,
        prefix: int = 0,