Few steps towards having 64-bit block numbers (#57)

Some of the other clients don't bother to store block numbers as
256-bit integers (64 bits or even 32 bit are enough).

The changes here are based on helpers introduced in eth_common
that try to abstract away all conversion steps in the code between
VM words and block numbers in variables in fields. Unfortunately,
this turn out to be more work than anticipated and I've postponed
finishing the refactoring for now (Block numbers are still 256 bit).

nimbus/constants.nim

@@ -53,7 +53,7 @@ let
 
   GAS_MOD_EXP_QUADRATIC_DENOMINATOR* = 20.u256
 
-  MAX_PREV_HEADER_DEPTH* = 256.u256
+  MAX_PREV_HEADER_DEPTH* =        256.toBlockNumber
 
   FORK_ICEAGE_BLKNUM* =           200_000.u256
   FORK_HOMESTED_BLKNUM* =         1_150_000.u256

nimbus/utils/header.nim

@@ -84,7 +84,7 @@ proc generateHeaderFromParentHeader*(
   # TODO: validateGt(timestamp, parent.timestamp)
   result = BlockHeader(
     timestamp: max(getTime(), parent.timestamp + 1.milliseconds),   # Note: Py-evm uses +1 second, not ms
-    blockNumber: (parent.blockNumber + 1.u256),
+    blockNumber: (parent.blockNumber + 1),
     # TODO: difficulty: parent.computeDifficulty(parent.timestamp),
     gasLimit: computeGasLimit(parent, gasLimitFloor = GENESIS_GAS_LIMIT),
     stateRoot: parent.stateRoot,

nimbus/vm/forks/f20150730_frontier/frontier_vm.nim

@@ -6,8 +6,8 @@
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
 import
+  stint, eth_common/eth_types,
   ../../../logging, ../../../constants, ../../../errors,
-  stint,
   ../../../block_types,
   ../../../vm/[base, stack], ../../../db/db_chain,  ../../../utils/header,
   ./frontier_block, ./frontier_vm_state, ./frontier_validation
@@ -22,7 +22,7 @@ method name*(vm: FrontierVM): string =
 method getBlockReward(vm: FrontierVM): UInt256 =
   BLOCK_REWARD
 
-method getUncleReward(vm: FrontierVM, blockNumber: UInt256, uncle: Block): UInt256 =
+method getUncleReward(vm: FrontierVM, blockNumber: BlockNumber, uncle: Block): UInt256 =
   BLOCK_REWARD * (UNCLE_DEPTH_PENALTY_FACTOR + uncle.blockNumber - blockNumber) div UNCLE_DEPTH_PENALTY_FACTOR
 
 

nimbus/vm/interpreter/opcodes_impl/block_ops.nim

@@ -6,7 +6,7 @@
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
 import
-  times, ./impl_std_import
+  times, eth_common/eth_types, ./impl_std_import
 
 {.this: computation.}
 {.experimental.}
@@ -15,7 +15,7 @@ using
   computation: var BaseComputation
 
 proc blockhash*(computation) =
-  let blockNumber = stack.popInt()
+  let blockNumber = vmWordToBlockNumber stack.popInt()
   let blockHash = vmState.getAncestorHash(blockNumber)
   stack.push(blockHash)
 
@@ -28,7 +28,7 @@ proc timestamp*(computation) =
   stack.push(vmState.timestamp.toUnix.uint64.u256)
 
 proc number*(computation) =
-  stack.push(vmState.blockNumber)
+  stack.push(blockNumberToVmWord vmState.blockNumber)
 
 proc difficulty*(computation) =
   stack.push(vmState.difficulty)

nimbus/vm_state.nim

@@ -66,12 +66,15 @@ method gasLimit*(vmState: BaseVMState): GasInt =
   vmState.blockHeader.gasLimit
 
 method getAncestorHash*(vmState: BaseVMState, blockNumber: BlockNumber): Hash256 =
-  var ancestorDepth = vmState.blockHeader.blockNumber - blockNumber - 1.u256
-  if ancestorDepth >= constants.MAX_PREV_HEADER_DEPTH or
-     ancestorDepth < 0 or
-     ancestorDepth >= vmState.prevHeaders.len.u256:
+  var ancestorDepth = vmState.blockHeader.blockNumber - blockNumber - 1
+  if ancestorDepth >= constants.MAX_PREV_HEADER_DEPTH or ancestorDepth < 0:
     return
-  var header = vmState.prevHeaders[ancestorDepth.toInt]
+
+  let idx = ancestorDepth.toInt
+  if idx >= vmState.prevHeaders.len:
+    return
+
+  var header = vmState.prevHeaders[idx]
   result = header.hash
 
 macro db*(vmState: untyped, readOnly: untyped, handler: untyped): untyped =