common: move big integer math to common/math (#3699)

* common: remove CurrencyToString

Move denomination values to params instead.

* common: delete dead code

* common: move big integer operations to common/math

This commit consolidates all big integer operations into common/math and
adds tests and documentation.

There should be no change in semantics for BigPow, BigMin, BigMax, S256,
U256, Exp and their behaviour is now locked in by tests.

The BigD, BytesToBig and Bytes2Big functions don't provide additional
value, all uses are replaced by new(big.Int).SetBytes().

BigToBytes is now called PaddedBigBytes, its minimum output size
parameter is now specified as the number of bytes instead of bits. The
single use of this function is in the EVM's MSTORE instruction.

Big and String2Big are replaced by ParseBig, which is slightly stricter.
It previously accepted leading zeros for hexadecimal inputs but treated
decimal inputs as octal if a leading zero digit was present.

ParseUint64 is used in places where String2Big was used to decode a
uint64.

The new functions MustParseBig and MustParseUint64 are now used in many
places where parsing errors were previously ignored.

* common: delete unused big integer variables

* accounts/abi: replace uses of BytesToBig with use of encoding/binary

* common: remove BytesToBig

* common: remove Bytes2Big

* common: remove BigTrue

* cmd/utils: add BigFlag and use it for error-checked integer flags

While here, remove environment variable processing for DirectoryFlag
because we don't use it.

* core: add missing error checks in genesis block parser

* common: remove String2Big

* cmd/evm: use utils.BigFlag

* common/math: check for 256 bit overflow in ParseBig

This is supposed to prevent silent overflow/truncation of values in the
genesis block JSON. Without this check, a genesis block that set a
balance larger than 256 bits would lead to weird behaviour in the VM.

* cmd/utils: fixup import

4 files changed, 22 insertions, 18 deletions

diff --git a/tests/state_test_util.go b/tests/state_test_util.go
index 064bf4588..81f49efa5 100644
--- a/tests/state_test_util.go
+++ b/tests/state_test_util.go
@@ -26,6 +26,7 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -170,11 +171,11 @@ func runStateTest(chainConfig *params.ChainConfig, test VmTest) error {
 			return fmt.Errorf("did not find expected post-state account: %s", addr)
 		}
 
-		if balance := statedb.GetBalance(address); balance.Cmp(common.Big(account.Balance)) != 0 {
-			return fmt.Errorf("(%x) balance failed. Expected: %v have: %v\n", address[:4], common.String2Big(account.Balance), balance)
+		if balance := statedb.GetBalance(address); balance.Cmp(math.MustParseBig256(account.Balance)) != 0 {
+			return fmt.Errorf("(%x) balance failed. Expected: %v have: %v\n", address[:4], math.MustParseBig256(account.Balance), balance)
 		}
 
-		if nonce := statedb.GetNonce(address); nonce != common.String2Big(account.Nonce).Uint64() {
+		if nonce := statedb.GetNonce(address); nonce != math.MustParseUint64(account.Nonce) {
 			return fmt.Errorf("(%x) nonce failed. Expected: %v have: %v\n", address[:4], account.Nonce, nonce)
 		}
 
@@ -205,7 +206,7 @@ func runStateTest(chainConfig *params.ChainConfig, test VmTest) error {
 
 func RunState(chainConfig *params.ChainConfig, statedb *state.StateDB, env, tx map[string]string) ([]byte, []*types.Log, *big.Int, error) {
 	environment, msg := NewEVMEnvironment(false, chainConfig, statedb, env, tx)
-	gaspool := new(core.GasPool).AddGas(common.Big(env["currentGasLimit"]))
+	gaspool := new(core.GasPool).AddGas(math.MustParseBig256(env["currentGasLimit"]))
 
 	root, _ := statedb.Commit(false)
 	statedb.Reset(root)
diff --git a/tests/transaction_test_util.go b/tests/transaction_test_util.go
index d26725867..1ecc73a67 100644
--- a/tests/transaction_test_util.go
+++ b/tests/transaction_test_util.go
@@ -24,6 +24,7 @@ import (
 	"runtime"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
@@ -161,7 +162,7 @@ func verifyTxFields(chainConfig *params.ChainConfig, txTest TransactionTest, dec
 
 	var decodedSender common.Address
 
-	signer := types.MakeSigner(chainConfig, common.String2Big(txTest.Blocknumber))
+	signer := types.MakeSigner(chainConfig, math.MustParseBig256(txTest.Blocknumber))
 	decodedSender, err = types.Sender(signer, decodedTx)
 	if err != nil {
 		return err
diff --git a/tests/util.go b/tests/util.go
index c96c2e06d..ce5b02fed 100644
--- a/tests/util.go
+++ b/tests/util.go
@@ -24,6 +24,7 @@ import (
 	"os"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -119,8 +120,8 @@ func insertAccount(state *state.StateDB, saddr string, account Account) {
 	}
 	addr := common.HexToAddress(saddr)
 	state.SetCode(addr, common.Hex2Bytes(account.Code))
-	state.SetNonce(addr, common.Big(account.Nonce).Uint64())
-	state.SetBalance(addr, common.Big(account.Balance))
+	state.SetNonce(addr, math.MustParseUint64(account.Nonce))
+	state.SetBalance(addr, math.MustParseBig256(account.Balance))
 	for a, v := range account.Storage {
 		state.SetState(addr, common.HexToHash(a), common.HexToHash(v))
 	}
@@ -152,10 +153,10 @@ type VmTest struct {
 func NewEVMEnvironment(vmTest bool, chainConfig *params.ChainConfig, statedb *state.StateDB, envValues map[string]string, tx map[string]string) (*vm.EVM, core.Message) {
 	var (
 		data  = common.FromHex(tx["data"])
-		gas   = common.Big(tx["gasLimit"])
-		price = common.Big(tx["gasPrice"])
-		value = common.Big(tx["value"])
-		nonce = common.Big(tx["nonce"]).Uint64()
+		gas   = math.MustParseBig256(tx["gasLimit"])
+		price = math.MustParseBig256(tx["gasPrice"])
+		value = math.MustParseBig256(tx["value"])
+		nonce = math.MustParseUint64(tx["nonce"])
 	)
 
 	origin := common.HexToAddress(tx["caller"])
@@ -198,10 +199,10 @@ func NewEVMEnvironment(vmTest bool, chainConfig *params.ChainConfig, statedb *st
 
 		Origin:      origin,
 		Coinbase:    common.HexToAddress(envValues["currentCoinbase"]),
-		BlockNumber: common.Big(envValues["currentNumber"]),
-		Time:        common.Big(envValues["currentTimestamp"]),
-		GasLimit:    common.Big(envValues["currentGasLimit"]),
-		Difficulty:  common.Big(envValues["currentDifficulty"]),
+		BlockNumber: math.MustParseBig256(envValues["currentNumber"]),
+		Time:        math.MustParseBig256(envValues["currentTimestamp"]),
+		GasLimit:    math.MustParseBig256(envValues["currentGasLimit"]),
+		Difficulty:  math.MustParseBig256(envValues["currentDifficulty"]),
 		GasPrice:    price,
 	}
 	if context.GasPrice == nil {
diff --git a/tests/vm_test_util.go b/tests/vm_test_util.go
index 4bf2dbfe9..d2ddee039 100644
--- a/tests/vm_test_util.go
+++ b/tests/vm_test_util.go
@@ -25,6 +25,7 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
@@ -180,7 +181,7 @@ func runVmTest(test VmTest) error {
 	if len(test.Gas) == 0 && err == nil {
 		return fmt.Errorf("gas unspecified, indicating an error. VM returned (incorrectly) successful")
 	} else {
-		gexp := common.Big(test.Gas)
+		gexp := math.MustParseBig256(test.Gas)
 		if gexp.Cmp(gas) != 0 {
 			return fmt.Errorf("gas failed. Expected %v, got %v\n", gexp, gas)
 		}
@@ -222,8 +223,8 @@ func RunVm(statedb *state.StateDB, env, exec map[string]string) ([]byte, []*type
 		to    = common.HexToAddress(exec["address"])
 		from  = common.HexToAddress(exec["caller"])
 		data  = common.FromHex(exec["data"])
-		gas   = common.Big(exec["gas"])
-		value = common.Big(exec["value"])
+		gas   = math.MustParseBig256(exec["gas"])
+		value = math.MustParseBig256(exec["value"])
 	)
 	caller := statedb.GetOrNewStateObject(from)
 	vm.PrecompiledContracts = make(map[common.Address]vm.PrecompiledContract)