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