From 97f73fd03dacd459b48381f4116b6ab588ecb71c Mon Sep 17 00:00:00 2001
From: jangko <jangko128@gmail.com>
Date: Thu, 19 Nov 2020 13:56:22 +0700
Subject: [PATCH] implement EIP 2046

---
 nimbus/constants.nim                          |  3 ++-
 nimbus/vm/interpreter/opcodes_impl.nim        |  9 ++++++-
 nimbus/vm/interpreter/utils/utils_numeric.nim |  7 +++++
 tests/all_tests.nim                           |  3 ++-
 tests/test_misc.nim                           | 26 +++++++++++++++++++
 5 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 tests/test_misc.nim

diff --git a/nimbus/constants.nim b/nimbus/constants.nim
index ea730110b..129759e5c 100644
--- a/nimbus/constants.nim
+++ b/nimbus/constants.nim
@@ -65,4 +65,5 @@ const
   # and: https://github.com/ethereum/EIPs/issues/170
   EIP170_CODE_SIZE_LIMIT* =                 24577
 
-
+  # EIP
+  MaxPrecompilesAddr* =                     0xFFFF
diff --git a/nimbus/vm/interpreter/opcodes_impl.nim b/nimbus/vm/interpreter/opcodes_impl.nim
index 68c15b382..67446d58c 100644
--- a/nimbus/vm/interpreter/opcodes_impl.nim
+++ b/nimbus/vm/interpreter/opcodes_impl.nim
@@ -731,7 +731,7 @@ template genCall(callName: untyped, opCode: Op): untyped =
                                     (memOutPos, memOutLen)
 
     let contractAddress = when opCode in {Call, StaticCall}: destination else: c.msg.contractAddress
-    let (childGasFee, childGasLimit) = c.gasCosts[opCode].c_handler(
+    var (childGasFee, childGasLimit) = c.gasCosts[opCode].c_handler(
       value,
       GasParams(kind: opCode,
                 c_isNewAccount: not c.accountExists(contractAddress),
@@ -742,6 +742,13 @@ template genCall(callName: untyped, opCode: Op): untyped =
                 c_memLength: memLength
       ))
 
+    # EIP 2046
+    # reduce gas fee for precompiles
+    # from 700 to 40
+    when opCode == StaticCall:
+      if c.fork >= FkBerlin and destination.toInt <= MaxPrecompilesAddr:
+        childGasFee = childGasFee - 660.GasInt
+
     if childGasFee >= 0:
       c.gasMeter.consumeGas(childGasFee, reason = $opCode)
 
diff --git a/nimbus/vm/interpreter/utils/utils_numeric.nim b/nimbus/vm/interpreter/utils/utils_numeric.nim
index a805d479b..1d9dad522 100644
--- a/nimbus/vm/interpreter/utils/utils_numeric.nim
+++ b/nimbus/vm/interpreter/utils/utils_numeric.nim
@@ -7,6 +7,7 @@
 
 import
   macros,
+  stew/endians2, stew/ranges/ptr_arith,
   eth/common/eth_types,
   ../../../constants
 
@@ -112,3 +113,9 @@ func safeInt*(x: Uint256): int {.inline.} =
   result = x.truncate(int)
   if x > high(int32).u256 or result < 0:
     result = high(int32)
+
+func toInt*(x: EthAddress): int =
+  type T = uint32
+  const len = sizeof(T)
+  fromBytesBE(T, makeOpenArray(x[x.len-len].unsafeAddr, len)).int
+  
\ No newline at end of file
diff --git a/tests/all_tests.nim b/tests/all_tests.nim
index 7c84c8c7d..ad9519dc0 100644
--- a/tests/all_tests.nim
+++ b/tests/all_tests.nim
@@ -113,4 +113,5 @@ cliBuilder:
           ./test_forkid,
           ../stateless/test_witness_keys,
           ../stateless/test_block_witness,
-          ../stateless/test_witness_json
+          ../stateless/test_witness_json,
+          ./test_misc
diff --git a/tests/test_misc.nim b/tests/test_misc.nim
new file mode 100644
index 000000000..7629500e4
--- /dev/null
+++ b/tests/test_misc.nim
@@ -0,0 +1,26 @@
+import
+  unittest2, stew/byteutils,
+  eth/common/eth_types,
+  ../nimbus/vm/interpreter/utils/utils_numeric
+
+func toAddress(n: int): EthAddress =
+  result[19] = n.byte
+  
+func toAddress(a, b: int): EthAddress =
+  result[18] = a.byte
+  result[19] = b.byte
+
+func toAddress(a, b, c: int): EthAddress =
+  result[17] = a.byte
+  result[18] = b.byte
+  result[19] = c.byte
+
+proc miscMain*() =
+  suite "Misc test suite":
+    test "EthAddress to int":
+      check toAddress(0xff).toInt == 0xFF
+      check toAddress(0x10, 0x0).toInt == 0x1000
+      check toAddress(0x10, 0x0, 0x0).toInt == 0x100000
+
+when isMainModule:
+  miscMain()