// parseBigInt treats the given bytes as a big-endian, signed integer and returns
// the result.
func parseBigInt(bytes []byte) *big.Int {
ret := new(big.Int)
if len(bytes) > 0 && bytes[0]&0x80 == 0x80 {
// This is a negative number.
notBytes := make([]byte, len(bytes))
for i := range notBytes {
notBytes[i] = ^bytes[i]
}
ret.SetBytes(notBytes)
ret.Add(ret, bigOne)
ret.Neg(ret)
return ret
}
ret.SetBytes(bytes)
return ret
}
func (curve *Curve) Add(p1, p2 *Point) *Point {
fmt.Printf("a")
if p1 == nil {
return p2
}
if p2 == nil {
return p1
}
lambda_numerator := new(big.Int)
lambda_denominator := new(big.Int)
lambda := new(big.Int)
lambda_numerator.Sub(p2.Y, p1.Y)
lambda_denominator.Sub(p2.X, p1.X)
if lambda_denominator.Cmp(BigZero) == -1 { //if Y is negative
lambda_denominator.Neg(lambda_denominator)
lambda_denominator.Sub(curve.P, lambda_denominator)
}
lambda_denominator, ok := modInverse(lambda_denominator, curve.P)
if !ok {
fmt.Printf("Add : Not ok\n")
return nil
}
lambda.Mul(lambda_numerator, lambda_denominator)
lambda = lambda.Mod(lambda, curve.P)
p3 := NewPoint()
p3.X.Exp(lambda, BigTwo, curve.P)
p3.X.Sub(p3.X, p1.X)
p3.X.Sub(p3.X, p2.X)
p3.X = p3.X.Mod(p3.X, curve.P)
p3.Y.Sub(p1.X, p3.X)
p3.Y.Mul(lambda, p3.Y)
p3.Y.Sub(p3.Y, p1.Y)
p3.Y = p3.Y.Mod(p3.Y, curve.P)
if p3.X.Cmp(BigZero) == -1 { //if X is negative
p3.X.Neg(p3.X)
p3.X.Sub(curve.P, p3.X)
}
if p3.Y.Cmp(BigZero) == -1 { //if Y is negative
p3.Y.Neg(p3.Y)
p3.Y.Sub(curve.P, p3.Y)
}
return p3
}
func B64ToBigInt(in string, b *big.Int) (err os.Error) {
bsize := base64.StdEncoding.DecodedLen(len(in))
buff := make([]byte, bsize)
n, err := base64.StdEncoding.Decode(buff, bytes.NewBufferString(in).Bytes())
neg := false
if err == nil {
buff = buff[0:n]
if buff[0]&0x80 == 0x80 {
neg = true
buff[0] &= 0x7f
}
b.SetBytes(buff)
// In case the passed in big was negative...
b.Abs(b)
if neg {
b.Neg(b)
}
}
return
}
