From 79b1169a9ff0b54ddf3b520a70a79c78ba5c988d Mon Sep 17 00:00:00 2001
From: Determinant <ted.sybil@gmail.com>
Date: Mon, 21 Oct 2019 14:47:51 -0400
Subject: customize Blockchain code

---
 core/evm.go | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 core/evm.go

(limited to 'core/evm.go')

diff --git a/core/evm.go b/core/evm.go
new file mode 100644
index 0000000..5c9d178
--- /dev/null
+++ b/core/evm.go
@@ -0,0 +1,97 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"math/big"
+
+	"github.com/ava-labs/go-ethereum/common"
+	"github.com/ava-labs/go-ethereum/consensus"
+	"github.com/ava-labs/go-ethereum/core/types"
+	"github.com/ava-labs/go-ethereum/core/vm"
+)
+
+// ChainContext supports retrieving headers and consensus parameters from the
+// current blockchain to be used during transaction processing.
+type ChainContext interface {
+	// Engine retrieves the chain's consensus engine.
+	Engine() consensus.Engine
+
+	// GetHeader returns the hash corresponding to their hash.
+	GetHeader(common.Hash, uint64) *types.Header
+}
+
+// NewEVMContext creates a new context for use in the EVM.
+func NewEVMContext(msg Message, header *types.Header, chain ChainContext, author *common.Address) vm.Context {
+	// If we don't have an explicit author (i.e. not mining), extract from the header
+	var beneficiary common.Address
+	if author == nil {
+		beneficiary, _ = chain.Engine().Author(header) // Ignore error, we're past header validation
+	} else {
+		beneficiary = *author
+	}
+	return vm.Context{
+		CanTransfer: CanTransfer,
+		Transfer:    Transfer,
+		GetHash:     GetHashFn(header, chain),
+		Origin:      msg.From(),
+		Coinbase:    beneficiary,
+		BlockNumber: new(big.Int).Set(header.Number),
+		Time:        new(big.Int).SetUint64(header.Time),
+		Difficulty:  new(big.Int).Set(header.Difficulty),
+		GasLimit:    header.GasLimit,
+		GasPrice:    new(big.Int).Set(msg.GasPrice()),
+	}
+}
+
+// GetHashFn returns a GetHashFunc which retrieves header hashes by number
+func GetHashFn(ref *types.Header, chain ChainContext) func(n uint64) common.Hash {
+	var cache map[uint64]common.Hash
+
+	return func(n uint64) common.Hash {
+		// If there's no hash cache yet, make one
+		if cache == nil {
+			cache = map[uint64]common.Hash{
+				ref.Number.Uint64() - 1: ref.ParentHash,
+			}
+		}
+		// Try to fulfill the request from the cache
+		if hash, ok := cache[n]; ok {
+			return hash
+		}
+		// Not cached, iterate the blocks and cache the hashes
+		for header := chain.GetHeader(ref.ParentHash, ref.Number.Uint64()-1); header != nil; header = chain.GetHeader(header.ParentHash, header.Number.Uint64()-1) {
+			cache[header.Number.Uint64()-1] = header.ParentHash
+			if n == header.Number.Uint64()-1 {
+				return header.ParentHash
+			}
+		}
+		return common.Hash{}
+	}
+}
+
+// CanTransfer checks whether there are enough funds in the address' account to make a transfer.
+// This does not take the necessary gas in to account to make the transfer valid.
+func CanTransfer(db vm.StateDB, addr common.Address, amount *big.Int) bool {
+	return db.GetBalance(addr).Cmp(amount) >= 0
+}
+
+// Transfer subtracts amount from sender and adds amount to recipient using the given Db
+func Transfer(db vm.StateDB, sender, recipient common.Address, amount *big.Int) {
+	db.SubBalance(sender, amount)
+	db.AddBalance(recipient, amount)
+}
-- 
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