common: improve documentation comments (#16701)

This commit adds many comments and removes unused code.
It also removes the EmptyHash function, which had some uses
but was silly.

9 files changed, 83 insertions, 137 deletions

diff --git a/common/bytes.go b/common/bytes.go
index e2adc8005..cbab2c3fa 100644
--- a/common/bytes.go
+++ b/common/bytes.go
@@ -19,15 +19,20 @@ package common
 
 import "encoding/hex"
 
+// ToHex returns the hex representation of b, prefixed with '0x'.
+// For empty slices, the return value is "0x0".
+//
+// Deprecated: use hexutil.Encode instead.
 func ToHex(b []byte) string {
 	hex := Bytes2Hex(b)
-	// Prefer output of "0x0" instead of "0x"
 	if len(hex) == 0 {
 		hex = "0"
 	}
 	return "0x" + hex
 }
 
+// FromHex returns the bytes represented by the hexadecimal string s.
+// s may be prefixed with "0x".
 func FromHex(s string) []byte {
 	if len(s) > 1 {
 		if s[0:2] == "0x" || s[0:2] == "0X" {
@@ -40,9 +45,7 @@ func FromHex(s string) []byte {
 	return Hex2Bytes(s)
 }
 
-// Copy bytes
-//
-// Returns an exact copy of the provided bytes
+// CopyBytes returns an exact copy of the provided bytes.
 func CopyBytes(b []byte) (copiedBytes []byte) {
 	if b == nil {
 		return nil
@@ -53,14 +56,17 @@ func CopyBytes(b []byte) (copiedBytes []byte) {
 	return
 }
 
+// hasHexPrefix validates str begins with '0x' or '0X'.
 func hasHexPrefix(str string) bool {
 	return len(str) >= 2 && str[0] == '0' && (str[1] == 'x' || str[1] == 'X')
 }
 
+// isHexCharacter returns bool of c being a valid hexadecimal.
 func isHexCharacter(c byte) bool {
 	return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') || ('A' <= c && c <= 'F')
 }
 
+// isHex validates whether each byte is valid hexadecimal string.
 func isHex(str string) bool {
 	if len(str)%2 != 0 {
 		return false
@@ -73,16 +79,18 @@ func isHex(str string) bool {
 	return true
 }
 
+// Bytes2Hex returns the hexadecimal encoding of d.
 func Bytes2Hex(d []byte) string {
 	return hex.EncodeToString(d)
 }
 
+// Hex2Bytes returns the bytes represented by the hexadecimal string str.
 func Hex2Bytes(str string) []byte {
 	h, _ := hex.DecodeString(str)
-
 	return h
 }
 
+// Hex2BytesFixed returns bytes of a specified fixed length flen.
 func Hex2BytesFixed(str string, flen int) []byte {
 	h, _ := hex.DecodeString(str)
 	if len(h) == flen {
@@ -96,6 +104,7 @@ func Hex2BytesFixed(str string, flen int) []byte {
 	return hh
 }
 
+// RightPadBytes zero-pads slice to the right up to length l.
 func RightPadBytes(slice []byte, l int) []byte {
 	if l <= len(slice) {
 		return slice
@@ -107,6 +116,7 @@ func RightPadBytes(slice []byte, l int) []byte {
 	return padded
 }
 
+// LeftPadBytes zero-pads slice to the left up to length l.
 func LeftPadBytes(slice []byte, l int) []byte {
 	if l <= len(slice) {
 		return slice
diff --git a/common/math/big.go b/common/math/big.go
index 787278650..dbf2770a9 100644
--- a/common/math/big.go
+++ b/common/math/big.go
@@ -78,7 +78,7 @@ func ParseBig256(s string) (*big.Int, bool) {
 	return bigint, ok
 }
 
-// MustParseBig parses s as a 256 bit big integer and panics if the string is invalid.
+// MustParseBig256 parses s as a 256 bit big integer and panics if the string is invalid.
 func MustParseBig256(s string) *big.Int {
 	v, ok := ParseBig256(s)
 	if !ok {
@@ -186,9 +186,8 @@ func U256(x *big.Int) *big.Int {
 func S256(x *big.Int) *big.Int {
 	if x.Cmp(tt255) < 0 {
 		return x
-	} else {
-		return new(big.Int).Sub(x, tt256)
 	}
+	return new(big.Int).Sub(x, tt256)
 }
 
 // Exp implements exponentiation by squaring.
diff --git a/common/number/int.go b/common/number/int.go
index 6dab2436d..5b5066970 100644
--- a/common/number/int.go
+++ b/common/number/int.go
@@ -34,13 +34,12 @@ func limitUnsigned256(x *Number) *Number {
 func limitSigned256(x *Number) *Number {
 	if x.num.Cmp(tt255) < 0 {
 		return x
-	} else {
-		x.num.Sub(x.num, tt256)
-		return x
 	}
+	x.num.Sub(x.num, tt256)
+	return x
 }
 
-// Number function
+// Initialiser is a Number function
 type Initialiser func(n int64) *Number
 
 // A Number represents a generic integer with a bounding function limiter. Limit is called after each operations
@@ -51,65 +50,65 @@ type Number struct {
 	limit func(n *Number) *Number
 }
 
-// Returns a new initialiser for a new *Number without having to expose certain fields
+// NewInitialiser returns a new initialiser for a new *Number without having to expose certain fields
 func NewInitialiser(limiter func(*Number) *Number) Initialiser {
 	return func(n int64) *Number {
 		return &Number{big.NewInt(n), limiter}
 	}
 }
 
-// Return a Number with a UNSIGNED limiter up to 256 bits
+// Uint256 returns a Number with a UNSIGNED limiter up to 256 bits
 func Uint256(n int64) *Number {
 	return &Number{big.NewInt(n), limitUnsigned256}
 }
 
-// Return a Number with a SIGNED limiter up to 256 bits
+// Int256 returns Number with a SIGNED limiter up to 256 bits
 func Int256(n int64) *Number {
 	return &Number{big.NewInt(n), limitSigned256}
 }
 
-// Returns a Number with a SIGNED unlimited size
+// Big returns a Number with a SIGNED unlimited size
 func Big(n int64) *Number {
 	return &Number{big.NewInt(n), func(x *Number) *Number { return x }}
 }
 
-// Sets i to sum of x+y
+// Add sets i to sum of x+y
 func (i *Number) Add(x, y *Number) *Number {
 	i.num.Add(x.num, y.num)
 	return i.limit(i)
 }
 
-// Sets i to difference of x-y
+// Sub sets i to difference of x-y
 func (i *Number) Sub(x, y *Number) *Number {
 	i.num.Sub(x.num, y.num)
 	return i.limit(i)
 }
 
-// Sets i to product of x*y
+// Mul sets i to product of x*y
 func (i *Number) Mul(x, y *Number) *Number {
 	i.num.Mul(x.num, y.num)
 	return i.limit(i)
 }
 
-// Sets i to the quotient prodject of x/y
+// Div sets i to the quotient prodject of x/y
 func (i *Number) Div(x, y *Number) *Number {
 	i.num.Div(x.num, y.num)
 	return i.limit(i)
 }
 
-// Sets i to x % y
+// Mod sets i to x % y
 func (i *Number) Mod(x, y *Number) *Number {
 	i.num.Mod(x.num, y.num)
 	return i.limit(i)
 }
 
-// Sets i to x << s
+// Lsh sets i to x << s
 func (i *Number) Lsh(x *Number, s uint) *Number {
 	i.num.Lsh(x.num, s)
 	return i.limit(i)
 }
 
-// Sets i to x^y
+// Pow sets i to x^y
 func (i *Number) Pow(x, y *Number) *Number {
 	i.num.Exp(x.num, y.num, big.NewInt(0))
 	return i.limit(i)
@@ -117,13 +116,13 @@ func (i *Number) Pow(x, y *Number) *Number {
 
 // Setters
 
-// Set x to i
+// Set sets x to i
 func (i *Number) Set(x *Number) *Number {
 	i.num.Set(x.num)
 	return i.limit(i)
 }
 
-// Set x bytes to i
+// SetBytes sets x bytes to i
 func (i *Number) SetBytes(x []byte) *Number {
 	i.num.SetBytes(x)
 	return i.limit(i)
@@ -140,12 +139,12 @@ func (i *Number) Cmp(x *Number) int {
 
 // Getters
 
-// Returns the string representation of i
+// String returns the string representation of i
 func (i *Number) String() string {
 	return i.num.String()
 }
 
-// Returns the byte representation of i
+// Bytes returns the byte representation of i
 func (i *Number) Bytes() []byte {
 	return i.num.Bytes()
 }
@@ -160,17 +159,17 @@ func (i *Number) Int64() int64 {
 	return i.num.Int64()
 }
 
-// Returns the signed version of i
+// Int256 returns the signed version of i
 func (i *Number) Int256() *Number {
 	return Int(0).Set(i)
 }
 
-// Returns the unsigned version of i
+// Uint256 returns the unsigned version of i
 func (i *Number) Uint256() *Number {
 	return Uint(0).Set(i)
 }
 
-// Returns the index of the first bit that's set to 1
+// FirstBitSet returns the index of the first bit that's set to 1
 func (i *Number) FirstBitSet() int {
 	for j := 0; j < i.num.BitLen(); j++ {
 		if i.num.Bit(j) > 0 {
diff --git a/common/path.go b/common/path.go
index bd8da86e7..69820cfe5 100644
--- a/common/path.go
+++ b/common/path.go
@@ -30,6 +30,7 @@ func MakeName(name, version string) string {
 	return fmt.Sprintf("%s/v%s/%s/%s", name, version, runtime.GOOS, runtime.Version())
 }
 
+// FileExist checks if a file exists at filePath.
 func FileExist(filePath string) bool {
 	_, err := os.Stat(filePath)
 	if err != nil && os.IsNotExist(err) {
@@ -39,9 +40,10 @@ func FileExist(filePath string) bool {
 	return true
 }
 
-func AbsolutePath(Datadir string, filename string) string {
+// AbsolutePath returns datadir + filename, or filename if it is absolute.
+func AbsolutePath(datadir string, filename string) string {
 	if filepath.IsAbs(filename) {
 		return filename
 	}
-	return filepath.Join(Datadir, filename)
+	return filepath.Join(datadir, filename)
 }
diff --git a/common/types.go b/common/types.go
index 0b94fb2c2..12c26d94b 100644
--- a/common/types.go
+++ b/common/types.go
@@ -42,19 +42,30 @@ var (
 // Hash represents the 32 byte Keccak256 hash of arbitrary data.
 type Hash [HashLength]byte
 
+// BytesToHash sets b to hash.
+// If b is larger than len(h), b will be cropped from the left.
 func BytesToHash(b []byte) Hash {
 	var h Hash
 	h.SetBytes(b)
 	return h
 }
+
+// BigToHash sets byte representation of b to hash.
+// If b is larger than len(h), b will be cropped from the left.
 func BigToHash(b *big.Int) Hash { return BytesToHash(b.Bytes()) }
-func HexToHash(s string) Hash   { return BytesToHash(FromHex(s)) }
 
-// Get the string representation of the underlying hash
-func (h Hash) Str() string   { return string(h[:]) }
+// HexToHash sets byte representation of s to hash.
+// If b is larger than len(h), b will be cropped from the left.
+func HexToHash(s string) Hash { return BytesToHash(FromHex(s)) }
+
+// Bytes gets the byte representation of the underlying hash.
 func (h Hash) Bytes() []byte { return h[:] }
+
+// Big converts a hash to a big integer.
 func (h Hash) Big() *big.Int { return new(big.Int).SetBytes(h[:]) }
-func (h Hash) Hex() string   { return hexutil.Encode(h[:]) }
+
+// Hex converts a hash to a hex string.
+func (h Hash) Hex() string { return hexutil.Encode(h[:]) }
 
 // TerminalString implements log.TerminalStringer, formatting a string for console
 // output during logging.
@@ -89,7 +100,8 @@ func (h Hash) MarshalText() ([]byte, error) {
 	return hexutil.Bytes(h[:]).MarshalText()
 }
 
-// Sets the hash to the value of b. If b is larger than len(h), 'b' will be cropped (from the left).
+// SetBytes sets the hash to the value of b.
+// If b is larger than len(h), b will be cropped from the left.
 func (h *Hash) SetBytes(b []byte) {
 	if len(b) > len(h) {
 		b = b[len(b)-HashLength:]
@@ -98,16 +110,6 @@ func (h *Hash) SetBytes(b []byte) {
 	copy(h[HashLength-len(b):], b)
 }
 
-// Set string `s` to h. If s is larger than len(h) s will be cropped (from left) to fit.
-func (h *Hash) SetString(s string) { h.SetBytes([]byte(s)) }
-
-// Sets h to other
-func (h *Hash) Set(other Hash) {
-	for i, v := range other {
-		h[i] = v
-	}
-}
-
 // Generate implements testing/quick.Generator.
 func (h Hash) Generate(rand *rand.Rand, size int) reflect.Value {
 	m := rand.Intn(len(h))
@@ -117,10 +119,6 @@ func (h Hash) Generate(rand *rand.Rand, size int) reflect.Value {
 	return reflect.ValueOf(h)
 }
 
-func EmptyHash(h Hash) bool {
-	return h == Hash{}
-}
-
 // UnprefixedHash allows marshaling a Hash without 0x prefix.
 type UnprefixedHash Hash
 
@@ -139,13 +137,21 @@ func (h UnprefixedHash) MarshalText() ([]byte, error) {
 // Address represents the 20 byte address of an Ethereum account.
 type Address [AddressLength]byte
 
+// BytesToAddress returns Address with value b.
+// If b is larger than len(h), b will be cropped from the left.
 func BytesToAddress(b []byte) Address {
 	var a Address
 	a.SetBytes(b)
 	return a
 }
+
+// BigToAddress returns Address with byte values of b.
+// If b is larger than len(h), b will be cropped from the left.
 func BigToAddress(b *big.Int) Address { return BytesToAddress(b.Bytes()) }
-func HexToAddress(s string) Address   { return BytesToAddress(FromHex(s)) }
+
+// HexToAddress returns Address with byte values of s.
+// If s is larger than len(h), s will be cropped from the left.
+func HexToAddress(s string) Address { return BytesToAddress(FromHex(s)) }
 
 // IsHexAddress verifies whether a string can represent a valid hex-encoded
 // Ethereum address or not.
@@ -156,11 +162,14 @@ func IsHexAddress(s string) bool {
 	return len(s) == 2*AddressLength && isHex(s)
 }
 
-// Get the string representation of the underlying address
-func (a Address) Str() string   { return string(a[:]) }
+// Bytes gets the string representation of the underlying address.
 func (a Address) Bytes() []byte { return a[:] }
+
+// Big converts an address to a big integer.
 func (a Address) Big() *big.Int { return new(big.Int).SetBytes(a[:]) }
-func (a Address) Hash() Hash    { return BytesToHash(a[:]) }
+
+// Hash converts an address to a hash by left-padding it with zeros.
+func (a Address) Hash() Hash { return BytesToHash(a[:]) }
 
 // Hex returns an EIP55-compliant hex string representation of the address.
 func (a Address) Hex() string {
@@ -184,7 +193,7 @@ func (a Address) Hex() string {
 	return "0x" + string(result)
 }
 
-// String implements the stringer interface and is used also by the logger.
+// String implements fmt.Stringer.
 func (a Address) String() string {
 	return a.Hex()
 }
@@ -195,7 +204,8 @@ func (a Address) Format(s fmt.State, c rune) {
 	fmt.Fprintf(s, "%"+string(c), a[:])
 }
 
-// Sets the address to the value of b. If b is larger than len(a) it will panic
+// SetBytes sets the address to the value of b.
+// If b is larger than len(a) it will panic.
 func (a *Address) SetBytes(b []byte) {
 	if len(b) > len(a) {
 		b = b[len(b)-AddressLength:]
@@ -203,16 +213,6 @@ func (a *Address) SetBytes(b []byte) {
 	copy(a[AddressLength-len(b):], b)
 }
 
-// Set string `s` to a. If s is larger than len(a) it will panic
-func (a *Address) SetString(s string) { a.SetBytes([]byte(s)) }
-
-// Sets a to other
-func (a *Address) Set(other Address) {
-	for i, v := range other {
-		a[i] = v
-	}
-}
-
 // MarshalText returns the hex representation of a.
 func (a Address) MarshalText() ([]byte, error) {
 	return hexutil.Bytes(a[:]).MarshalText()
@@ -228,7 +228,7 @@ func (a *Address) UnmarshalJSON(input []byte) error {
 	return hexutil.UnmarshalFixedJSON(addressT, input, a[:])
 }
 
-// UnprefixedHash allows marshaling an Address without 0x prefix.
+// UnprefixedAddress allows marshaling an Address without 0x prefix.
 type UnprefixedAddress Address
 
 // UnmarshalText decodes the address from hex. The 0x prefix is optional.
diff --git a/common/types_template.go b/common/types_template.go
deleted file mode 100644
index 9a8f29977..000000000
--- a/common/types_template.go
+++ /dev/null
@@ -1,64 +0,0 @@
-// Copyright 2015 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/>.
-
-// +build none
-//sed -e 's/_N_/Hash/g' -e 's/_S_/32/g' -e '1d' types_template.go | gofmt -w hash.go
-
-package common
-
-import "math/big"
-
-type _N_ [_S_]byte
-
-func BytesTo_N_(b []byte) _N_ {
-	var h _N_
-	h.SetBytes(b)
-	return h
-}
-func StringTo_N_(s string) _N_ { return BytesTo_N_([]byte(s)) }
-func BigTo_N_(b *big.Int) _N_  { return BytesTo_N_(b.Bytes()) }
-func HexTo_N_(s string) _N_    { return BytesTo_N_(FromHex(s)) }
-
-// Don't use the default 'String' method in case we want to overwrite
-
-// Get the string representation of the underlying hash
-func (h _N_) Str() string   { return string(h[:]) }
-func (h _N_) Bytes() []byte { return h[:] }
-func (h _N_) Big() *big.Int { return new(big.Int).SetBytes(h[:]) }
-func (h _N_) Hex() string   { return "0x" + Bytes2Hex(h[:]) }
-
-// Sets the hash to the value of b. If b is larger than len(h) it will panic
-func (h *_N_) SetBytes(b []byte) {
-	// Use the right most bytes
-	if len(b) > len(h) {
-		b = b[len(b)-_S_:]
-	}
-
-	// Reverse the loop
-	for i := len(b) - 1; i >= 0; i-- {
-		h[_S_-len(b)+i] = b[i]
-	}
-}
-
-// Set string `s` to h. If s is larger than len(h) it will panic
-func (h *_N_) SetString(s string) { h.SetBytes([]byte(s)) }
-
-// Sets h to other
-func (h *_N_) Set(other _N_) {
-	for i, v := range other {
-		h[i] = v
-	}
-}
diff --git a/core/state/state_test.go b/core/state/state_test.go
index 12778f6f1..123559ea9 100644
--- a/core/state/state_test.go
+++ b/core/state/state_test.go
@@ -99,7 +99,7 @@ func (s *StateSuite) TestNull(c *checker.C) {
 	s.state.SetState(address, common.Hash{}, value)
 	s.state.Commit(false)
 	value = s.state.GetState(address, common.Hash{})
-	if !common.EmptyHash(value) {
+	if value != (common.Hash{}) {
 		c.Errorf("expected empty hash. got %x", value)
 	}
 }
diff --git a/core/vm/gas_table.go b/core/vm/gas_table.go
index 83adba428..0764c67a4 100644
--- a/core/vm/gas_table.go
+++ b/core/vm/gas_table.go
@@ -124,12 +124,12 @@ func gasSStore(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, m
 	// 1. From a zero-value address to a non-zero value         (NEW VALUE)
 	// 2. From a non-zero value address to a zero-value address (DELETE)
 	// 3. From a non-zero to a non-zero                         (CHANGE)
-	if common.EmptyHash(val) && !common.EmptyHash(common.BigToHash(y)) {
+	if val == (common.Hash{}) && y.Sign() != 0 {
 		// 0 => non 0
 		return params.SstoreSetGas, nil
-	} else if !common.EmptyHash(val) && common.EmptyHash(common.BigToHash(y)) {
+	} else if val != (common.Hash{}) && y.Sign() == 0 {
+		// non 0 => 0
 		evm.StateDB.AddRefund(params.SstoreRefundGas)
-
 		return params.SstoreClearGas, nil
 	} else {
 		// non 0 => non 0 (or 0 => 0)
diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index dc2335492..51c593601 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -680,7 +680,7 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
 		}
 	}
 	// If the head fetch already found an ancestor, return
-	if !common.EmptyHash(hash) {
+	if hash != (common.Hash{}) {
 		if int64(number) <= floor {
 			p.log.Warn("Ancestor below allowance", "number", number, "hash", hash, "allowance", floor)
 			return 0, errInvalidAncestor