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package common
import "math/big"
// Common big integers often used
var (
Big1 = big.NewInt(1)
Big2 = big.NewInt(2)
Big3 = big.NewInt(3)
Big0 = big.NewInt(0)
BigTrue = Big1
BigFalse = Big0
Big32 = big.NewInt(32)
Big256 = big.NewInt(0xff)
Big257 = big.NewInt(257)
)
// Big pow
//
// Returns the power of two big integers
func BigPow(a, b int) *big.Int {
c := new(big.Int)
c.Exp(big.NewInt(int64(a)), big.NewInt(int64(b)), big.NewInt(0))
return c
}
// Big
//
// Shortcut for new(big.Int).SetString(..., 0)
func Big(num string) *big.Int {
n := new(big.Int)
n.SetString(num, 0)
return n
}
// BigD
//
// Shortcut for new(big.Int).SetBytes(...)
func Bytes2Big(data []byte) *big.Int {
n := new(big.Int)
n.SetBytes(data)
return n
}
func BigD(data []byte) *big.Int { return Bytes2Big(data) }
func String2Big(num string) *big.Int {
n := new(big.Int)
n.SetString(num, 0)
return n
}
func BitTest(num *big.Int, i int) bool {
return num.Bit(i) > 0
}
// To256
//
// "cast" the big int to a 256 big int (i.e., limit to)
var tt256 = new(big.Int).Lsh(big.NewInt(1), 256)
var tt256m1 = new(big.Int).Sub(new(big.Int).Lsh(big.NewInt(1), 256), big.NewInt(1))
var tt255 = new(big.Int).Lsh(big.NewInt(1), 255)
func U256(x *big.Int) *big.Int {
//if x.Cmp(Big0) < 0 {
// return new(big.Int).Add(tt256, x)
// }
x.And(x, tt256m1)
return x
}
func S256(x *big.Int) *big.Int {
if x.Cmp(tt255) < 0 {
return x
} else {
// We don't want to modify x, ever
return new(big.Int).Sub(x, tt256)
}
}
func FirstBitSet(v *big.Int) int {
for i := 0; i < v.BitLen(); i++ {
if v.Bit(i) > 0 {
return i
}
}
return v.BitLen()
}
// Big to bytes
//
// Returns the bytes of a big integer with the size specified by **base**
// Attempts to pad the byte array with zeros.
func BigToBytes(num *big.Int, base int) []byte {
ret := make([]byte, base/8)
if len(num.Bytes()) > base/8 {
return num.Bytes()
}
return append(ret[:len(ret)-len(num.Bytes())], num.Bytes()...)
}
// Big copy
//
// Creates a copy of the given big integer
func BigCopy(src *big.Int) *big.Int {
return new(big.Int).Set(src)
}
// Big max
//
// Returns the maximum size big integer
func BigMax(x, y *big.Int) *big.Int {
if x.Cmp(y) < 0 {
return y
}
return x
}
// Big min
//
// Returns the minimum size big integer
func BigMin(x, y *big.Int) *big.Int {
if x.Cmp(y) > 0 {
return y
}
return x
}
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