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

1 files changed, 12 insertions, 12 deletions

diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index a2e4ac814..25c3a1ada 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -179,10 +179,10 @@ var (
 		Usage: "Number of CPU threads to use for mining",
 		Value: runtime.NumCPU(),
 	}
-	TargetGasLimitFlag = cli.StringFlag{
+	TargetGasLimitFlag = cli.Uint64Flag{
 		Name:  "targetgaslimit",
 		Usage: "Target gas limit sets the artificial target gas floor for the blocks to mine",
-		Value: params.GenesisGasLimit.String(),
+		Value: params.GenesisGasLimit.Uint64(),
 	}
 	AutoDAGFlag = cli.BoolFlag{
 		Name:  "autodag",
@@ -193,10 +193,10 @@ var (
 		Usage: "Public address for block mining rewards (default = first account created)",
 		Value: "0",
 	}
-	GasPriceFlag = cli.StringFlag{
+	GasPriceFlag = BigFlag{
 		Name:  "gasprice",
 		Usage: "Minimal gas price to accept for mining a transactions",
-		Value: new(big.Int).Mul(big.NewInt(20), common.Shannon).String(),
+		Value: big.NewInt(20 * params.Shannon),
 	}
 	ExtraDataFlag = cli.StringFlag{
 		Name:  "extradata",
@@ -382,15 +382,15 @@ var (
 	}
 
 	// Gas price oracle settings
-	GpoMinGasPriceFlag = cli.StringFlag{
+	GpoMinGasPriceFlag = BigFlag{
 		Name:  "gpomin",
 		Usage: "Minimum suggested gas price",
-		Value: new(big.Int).Mul(big.NewInt(20), common.Shannon).String(),
+		Value: big.NewInt(20 * params.Shannon),
 	}
-	GpoMaxGasPriceFlag = cli.StringFlag{
+	GpoMaxGasPriceFlag = BigFlag{
 		Name:  "gpomax",
 		Usage: "Maximum suggested gas price",
-		Value: new(big.Int).Mul(big.NewInt(500), common.Shannon).String(),
+		Value: big.NewInt(500 * params.Shannon),
 	}
 	GpoFullBlockRatioFlag = cli.IntFlag{
 		Name:  "gpofull",
@@ -741,9 +741,9 @@ func RegisterEthService(ctx *cli.Context, stack *node.Node, extra []byte) {
 		MinerThreads:            ctx.GlobalInt(MinerThreadsFlag.Name),
 		ExtraData:               MakeMinerExtra(extra, ctx),
 		DocRoot:                 ctx.GlobalString(DocRootFlag.Name),
-		GasPrice:                common.String2Big(ctx.GlobalString(GasPriceFlag.Name)),
-		GpoMinGasPrice:          common.String2Big(ctx.GlobalString(GpoMinGasPriceFlag.Name)),
-		GpoMaxGasPrice:          common.String2Big(ctx.GlobalString(GpoMaxGasPriceFlag.Name)),
+		GasPrice:                GlobalBig(ctx, GasPriceFlag.Name),
+		GpoMinGasPrice:          GlobalBig(ctx, GpoMinGasPriceFlag.Name),
+		GpoMaxGasPrice:          GlobalBig(ctx, GpoMaxGasPriceFlag.Name),
 		GpoFullBlockRatio:       ctx.GlobalInt(GpoFullBlockRatioFlag.Name),
 		GpobaseStepDown:         ctx.GlobalInt(GpobaseStepDownFlag.Name),
 		GpobaseStepUp:           ctx.GlobalInt(GpobaseStepUpFlag.Name),
@@ -819,7 +819,7 @@ func RegisterEthStatsService(stack *node.Node, url string) {
 
 // SetupNetwork configures the system for either the main net or some test network.
 func SetupNetwork(ctx *cli.Context) {
-	params.TargetGasLimit = common.String2Big(ctx.GlobalString(TargetGasLimitFlag.Name))
+	params.TargetGasLimit = new(big.Int).SetUint64(ctx.GlobalUint64(TargetGasLimitFlag.Name))
 }
 
 // MakeChainConfig reads the chain configuration from the database in ctx.Datadir.