1 files changed, 143 insertions, 0 deletions
diff --git a/common/math/big.go b/common/math/big.go
new file mode 100644
index 000000000..c0508c102
--- /dev/null
+++ b/common/math/big.go
@@ -0,0 +1,143 @@
+// Copyright 2017 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/>.
+
+// Package math provides integer math utilities.
+package math
+
+import (
+	"math/big"
+)
+
+var (
+	tt255     = BigPow(2, 255)
+	tt256     = BigPow(2, 256)
+	tt256m1   = new(big.Int).Sub(tt256, big.NewInt(1))
+	MaxBig256 = new(big.Int).Set(tt256m1)
+)
+
+// ParseBig256 parses s as a 256 bit integer in decimal or hexadecimal syntax.
+// Leading zeros are accepted. The empty string parses as zero.
+func ParseBig256(s string) (*big.Int, bool) {
+	if s == "" {
+		return new(big.Int), true
+	}
+	var bigint *big.Int
+	var ok bool
+	if len(s) >= 2 && (s[:2] == "0x" || s[:2] == "0X") {
+		bigint, ok = new(big.Int).SetString(s[2:], 16)
+	} else {
+		bigint, ok = new(big.Int).SetString(s, 10)
+	}
+	if ok && bigint.BitLen() > 256 {
+		bigint, ok = nil, false
+	}
+	return bigint, ok
+}
+
+// MustParseBig 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 {
+		panic("invalid 256 bit integer: " + s)
+	}
+	return v
+}
+
+// BigPow returns a ** b as a big integer.
+func BigPow(a, b int64) *big.Int {
+	r := big.NewInt(a)
+	return r.Exp(r, big.NewInt(b), nil)
+}
+
+// BigMax returns the larger of x or y.
+func BigMax(x, y *big.Int) *big.Int {
+	if x.Cmp(y) < 0 {
+		return y
+	}
+	return x
+}
+
+// BigMin returns the smaller of x or y.
+func BigMin(x, y *big.Int) *big.Int {
+	if x.Cmp(y) > 0 {
+		return y
+	}
+	return x
+}
+
+// FirstBitSet returns the index of the first 1 bit in v, counting from LSB.
+func FirstBitSet(v *big.Int) int {
+	for i := 0; i < v.BitLen(); i++ {
+		if v.Bit(i) > 0 {
+			return i
+		}
+	}
+	return v.BitLen()
+}
+
+// PaddedBigBytes encodes a big integer as a big-endian byte slice. The length
+// of the slice is at least n bytes.
+func PaddedBigBytes(bigint *big.Int, n int) []byte {
+	bytes := bigint.Bytes()
+	if len(bytes) >= n {
+		return bytes
+	}
+	ret := make([]byte, n)
+	return append(ret[:len(ret)-len(bytes)], bytes...)
+}
+
+// U256 encodes as a 256 bit two's complement number. This operation is destructive.
+func U256(x *big.Int) *big.Int {
+	return x.And(x, tt256m1)
+}
+
+// S256 interprets x as a two's complement number.
+// x must not exceed 256 bits (the result is undefined if it does) and is not modified.
+//
+//   S256(0)        = 0
+//   S256(1)        = 1
+//   S256(2**255)   = -2**255
+//   S256(2**256-1) = -1
+func S256(x *big.Int) *big.Int {
+	if x.Cmp(tt255) < 0 {
+		return x
+	} else {
+		return new(big.Int).Sub(x, tt256)
+	}
+}
+
+// wordSize is the size number of bits in a big.Word.
+const wordSize = 32 << (uint64(^big.Word(0)) >> 63)
+
+// Exp implements exponentiation by squaring.
+// Exp returns a newly-allocated big integer and does not change
+// base or exponent. The result is truncated to 256 bits.
+//
+// Courtesy @karalabe and @chfast
+func Exp(base, exponent *big.Int) *big.Int {
+	result := big.NewInt(1)
+
+	for _, word := range exponent.Bits() {
+		for i := 0; i < wordSize; i++ {
+			if word&1 == 1 {
+				U256(result.Mul(result, base))
+			}
+			U256(base.Mul(base, base))
+			word >>= 1
+		}
+	}
+	return result
+}