From 62968bf733bd188da10dda504380ea9efe4b9455 Mon Sep 17 00:00:00 2001
From: coffeepots <coffeepotsgh@gmail.com>
Date: Tue, 2 Oct 2018 15:46:39 +0100
Subject: [PATCH] Initial support for precompiles with ecRecover

---
 nimbus/vm/precompiles.nim | 55 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 nimbus/vm/precompiles.nim

diff --git a/nimbus/vm/precompiles.nim b/nimbus/vm/precompiles.nim
new file mode 100644
index 000000000..58e7637cd
--- /dev/null
+++ b/nimbus/vm/precompiles.nim
@@ -0,0 +1,55 @@
+import
+  ../vm_types, interpreter/[gas_meter, gas_costs],
+  ../errors, stint, eth_keys, eth_common, chronicles, tables, macros,
+  message
+
+type
+  PrecompileAddresses = enum
+    paEcRecover = 1,
+    paSha256,
+    paRipeMd160,
+    paIdentity,
+    #
+    paModExp,
+    paEcAdd,
+    paEcMul,
+    paPairing = 8
+
+proc getSignature*(computation: BaseComputation): Signature =
+  var bytes: array[128, byte]
+  bytes[0..31] = computation.msg.data[32..63]   # V
+  bytes[32..63] = computation.msg.data[64..95]  # R
+  bytes[64..63] = computation.msg.data[96..128] # S
+  result = initSignature(bytes)                 # Can raise
+
+proc ecRecover*(computation: var BaseComputation) =
+  computation.gasMeter.consumeGas(
+    GAS_ECRECOVER,
+    reason="ECRecover Precompile")
+
+  # TODO: Check endian
+  # Assumes V is 27 or 28
+  var
+    sig = computation.getSignature()
+    pubKey: PublicKey
+  let msgHash = computation.msg.data[0..31]
+
+  if sig.recoverSignatureKey(msgHash, pubKey) != EthKeysStatus.Success:
+    raise newException(ValidationError, "Could not derive public key from computation")
+  
+  computation.rawOutput = @(pubKey.toCanonicalAddress())
+  debug "ECRecover derived key ", key = pubKey.toCanonicalAddress()
+
+proc execPrecompiles*(computation: var BaseComputation): bool {.inline.} =
+  # TODO: Assumes endian
+  for i in 0..18:
+    if computation.msg.codeAddress[i] != 0: return
+  let lb = computation.msg.codeAddress[19]
+  if lb < 9:
+    result = true
+    let precompile = PrecompileAddresses(lb)
+    debug "Call precompile ", precompile = precompile, codeAddr = computation.msg.codeAddress
+    case precompile
+    of paEcRecover: ecRecover(computation)
+    else:
+      raise newException(ValidationError, "Unknown precompile address " & $lb)