core: vm: implement RAND opcode support

DEXON has a built-in on chain random oracle that allow one to retrieve a
random variable. Add a new opcode `RAND` to load the random variable
onto the stack.

1 files changed, 22 insertions, 0 deletions

diff --git a/core/vm/instructions.go b/core/vm/instructions.go
index 349f407a2..de0fcaeb6 100644
--- a/core/vm/instructions.go
+++ b/core/vm/instructions.go
@@ -17,6 +17,7 @@
 package vm
 
 import (
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"math/big"
@@ -24,6 +25,7 @@ import (
 	"github.com/dexon-foundation/dexon/common"
 	"github.com/dexon-foundation/dexon/common/math"
 	"github.com/dexon-foundation/dexon/core/types"
+	"github.com/dexon-foundation/dexon/crypto"
 	"github.com/dexon-foundation/dexon/params"
 	"golang.org/x/crypto/sha3"
 )
@@ -404,6 +406,26 @@ func opSha3(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory
 	return nil, nil
 }
 
+func opRand(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
+	evm := interpreter.evm
+
+	nonce := evm.StateDB.GetNonce(contract.Caller())
+	binaryNonce := make([]byte, binary.MaxVarintLen64)
+	binary.PutUvarint(binaryNonce, nonce)
+
+	binaryGas := make([]byte, binary.MaxVarintLen64)
+	binary.PutUvarint(binaryGas, contract.Gas)
+
+	hash := crypto.Keccak256(
+		evm.Randomness,
+		contract.Caller().Bytes(),
+		binaryNonce,
+		binaryGas)
+
+	stack.push(interpreter.intPool.get().SetBytes(hash))
+	return nil, nil
+}
+
 func opAddress(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	stack.push(contract.Address().Big())
 	return nil, nil