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

3 files changed, 47 insertions, 57 deletions

diff --git a/accounts/abi/abi.go b/accounts/abi/abi.go
index 627a2a0c4..3d1010229 100644
--- a/accounts/abi/abi.go
+++ b/accounts/abi/abi.go
@@ -17,6 +17,7 @@
 package abi
 
 import (
+	"encoding/binary"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -129,16 +130,15 @@ func toGoSlice(i int, t Argument, output []byte) (interface{}, error) {
 	var size int
 	var offset int
 	if t.Type.IsSlice {
-
 		// get the offset which determines the start of this array ...
-		offset = int(common.BytesToBig(output[index : index+32]).Uint64())
+		offset = int(binary.BigEndian.Uint64(output[index+24 : index+32]))
 		if offset+32 > len(output) {
 			return nil, fmt.Errorf("abi: cannot marshal in to go slice: offset %d would go over slice boundary (len=%d)", len(output), offset+32)
 		}
 
 		slice = output[offset:]
 		// ... starting with the size of the array in elements ...
-		size = int(common.BytesToBig(slice[:32]).Uint64())
+		size = int(binary.BigEndian.Uint64(slice[24:32]))
 		slice = slice[32:]
 		// ... and make sure that we've at the very least the amount of bytes
 		// available in the buffer.
@@ -147,7 +147,7 @@ func toGoSlice(i int, t Argument, output []byte) (interface{}, error) {
 		}
 
 		// reslice to match the required size
-		slice = slice[:(size * 32)]
+		slice = slice[:size*32]
 	} else if t.Type.IsArray {
 		//get the number of elements in the array
 		size = t.Type.SliceSize
@@ -165,33 +165,12 @@ func toGoSlice(i int, t Argument, output []byte) (interface{}, error) {
 			inter        interface{}             // interface type
 			returnOutput = slice[i*32 : i*32+32] // the return output
 		)
-
 		// set inter to the correct type (cast)
 		switch elem.T {
 		case IntTy, UintTy:
-			bigNum := common.BytesToBig(returnOutput)
-			switch t.Type.Kind {
-			case reflect.Uint8:
-				inter = uint8(bigNum.Uint64())
-			case reflect.Uint16:
-				inter = uint16(bigNum.Uint64())
-			case reflect.Uint32:
-				inter = uint32(bigNum.Uint64())
-			case reflect.Uint64:
-				inter = bigNum.Uint64()
-			case reflect.Int8:
-				inter = int8(bigNum.Int64())
-			case reflect.Int16:
-				inter = int16(bigNum.Int64())
-			case reflect.Int32:
-				inter = int32(bigNum.Int64())
-			case reflect.Int64:
-				inter = bigNum.Int64()
-			default:
-				inter = common.BytesToBig(returnOutput)
-			}
+			inter = readInteger(t.Type.Kind, returnOutput)
 		case BoolTy:
-			inter = common.BytesToBig(returnOutput).Uint64() > 0
+			inter = !allZero(returnOutput)
 		case AddressTy:
 			inter = common.BytesToAddress(returnOutput)
 		case HashTy:
@@ -207,6 +186,38 @@ func toGoSlice(i int, t Argument, output []byte) (interface{}, error) {
 	return refSlice.Interface(), nil
 }
 
+func readInteger(kind reflect.Kind, b []byte) interface{} {
+	switch kind {
+	case reflect.Uint8:
+		return uint8(b[len(b)-1])
+	case reflect.Uint16:
+		return binary.BigEndian.Uint16(b[len(b)-2:])
+	case reflect.Uint32:
+		return binary.BigEndian.Uint32(b[len(b)-4:])
+	case reflect.Uint64:
+		return binary.BigEndian.Uint64(b[len(b)-8:])
+	case reflect.Int8:
+		return int8(b[len(b)-1])
+	case reflect.Int16:
+		return int16(binary.BigEndian.Uint16(b[len(b)-2:]))
+	case reflect.Int32:
+		return int32(binary.BigEndian.Uint32(b[len(b)-4:]))
+	case reflect.Int64:
+		return int64(binary.BigEndian.Uint64(b[len(b)-8:]))
+	default:
+		return new(big.Int).SetBytes(b)
+	}
+}
+
+func allZero(b []byte) bool {
+	for _, byte := range b {
+		if byte != 0 {
+			return false
+		}
+	}
+	return true
+}
+
 // toGoType parses the input and casts it to the proper type defined by the ABI
 // argument in T.
 func toGoType(i int, t Argument, output []byte) (interface{}, error) {
@@ -226,12 +237,12 @@ func toGoType(i int, t Argument, output []byte) (interface{}, error) {
 	switch t.Type.T {
 	case StringTy, BytesTy: // variable arrays are written at the end of the return bytes
 		// parse offset from which we should start reading
-		offset := int(common.BytesToBig(output[index : index+32]).Uint64())
+		offset := int(binary.BigEndian.Uint64(output[index+24 : index+32]))
 		if offset+32 > len(output) {
 			return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32)
 		}
 		// parse the size up until we should be reading
-		size := int(common.BytesToBig(output[offset : offset+32]).Uint64())
+		size := int(binary.BigEndian.Uint64(output[offset+24 : offset+32]))
 		if offset+32+size > len(output) {
 			return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32+size)
 		}
@@ -245,32 +256,9 @@ func toGoType(i int, t Argument, output []byte) (interface{}, error) {
 	// convert the bytes to whatever is specified by the ABI.
 	switch t.Type.T {
 	case IntTy, UintTy:
-		bigNum := common.BytesToBig(returnOutput)
-
-		// If the type is a integer convert to the integer type
-		// specified by the ABI.
-		switch t.Type.Kind {
-		case reflect.Uint8:
-			return uint8(bigNum.Uint64()), nil
-		case reflect.Uint16:
-			return uint16(bigNum.Uint64()), nil
-		case reflect.Uint32:
-			return uint32(bigNum.Uint64()), nil
-		case reflect.Uint64:
-			return uint64(bigNum.Uint64()), nil
-		case reflect.Int8:
-			return int8(bigNum.Int64()), nil
-		case reflect.Int16:
-			return int16(bigNum.Int64()), nil
-		case reflect.Int32:
-			return int32(bigNum.Int64()), nil
-		case reflect.Int64:
-			return int64(bigNum.Int64()), nil
-		case reflect.Ptr:
-			return bigNum, nil
-		}
+		return readInteger(t.Type.Kind, returnOutput), nil
 	case BoolTy:
-		return common.BytesToBig(returnOutput).Uint64() > 0, nil
+		return !allZero(returnOutput), nil
 	case AddressTy:
 		return common.BytesToAddress(returnOutput), nil
 	case HashTy:
diff --git a/accounts/abi/bind/backends/simulated.go b/accounts/abi/bind/backends/simulated.go
index 1c34ba0e7..5e2fcbae7 100644
--- a/accounts/abi/bind/backends/simulated.go
+++ b/accounts/abi/bind/backends/simulated.go
@@ -25,6 +25,7 @@ import (
 	"github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/accounts/abi/bind"
 	"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"
@@ -244,7 +245,7 @@ func (b *SimulatedBackend) callContract(ctx context.Context, call ethereum.CallM
 	}
 	// Set infinite balance to the fake caller account.
 	from := statedb.GetOrNewStateObject(call.From)
-	from.SetBalance(common.MaxBig)
+	from.SetBalance(math.MaxBig256)
 	// Execute the call.
 	msg := callmsg{call}
 
@@ -252,7 +253,7 @@ func (b *SimulatedBackend) callContract(ctx context.Context, call ethereum.CallM
 	// Create a new environment which holds all relevant information
 	// about the transaction and calling mechanisms.
 	vmenv := vm.NewEVM(evmContext, statedb, chainConfig, vm.Config{})
-	gaspool := new(core.GasPool).AddGas(common.MaxBig)
+	gaspool := new(core.GasPool).AddGas(math.MaxBig256)
 	ret, gasUsed, _, err := core.NewStateTransition(vmenv, msg, gaspool).TransitionDb()
 	return ret, gasUsed, err
 }
diff --git a/accounts/abi/numbers.go b/accounts/abi/numbers.go
index 3d5842292..36fb6705e 100644
--- a/accounts/abi/numbers.go
+++ b/accounts/abi/numbers.go
@@ -21,6 +21,7 @@ import (
 	"reflect"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 )
 
 var (
@@ -58,7 +59,7 @@ var (
 
 // U256 converts a big Int into a 256bit EVM number.
 func U256(n *big.Int) []byte {
-	return common.LeftPadBytes(common.U256(n).Bytes(), 32)
+	return common.LeftPadBytes(math.U256(n).Bytes(), 32)
 }
 
 // packNum packs the given number (using the reflect value) and will cast it to appropriate number representation