Quote from: pooya87 on September 18, 2020, 06:17:44 AM

this topic is already filled with many examples!
i think you should start at the basics and read what Elliptic Curve Cryptography and Modular Arithmetic are before trying to come up with the code that computes half of a public key!
start here: https://en.wikipedia.org/wiki/Modular_arithmetic
then:
https://blog.cloudflare.com/a-relatively-easy-to-understand-primer-on-elliptic-curve-cryptography/
https://en.wikipedia.org/wiki/Elliptic-curve_cryptography
and finally
https://en.wikipedia.org/wiki/Elliptic_curve_point_multiplication
https://en.wikipedia.org/wiki/Modular_multiplicative_inverse

Thanks for the links, I have a bit of a headache but now I have the basics to understand.
Well, I now know how to divide a point by 2 as in my example (private key 10). On the other hand, I realize after several tests that if the point to be divided corresponds to an odd private key, the result no longer corresponds to what I expected. As long as the private key is divisible by 2, the calculations seem to respect a certain logic but since the division does not give a whole number (without comma), this "rule" is shattered ^^.
Can someone explain to me this part:
3. If d is odd let P = P + Q
4. Double Q: Q = 2 * Q, halve d rounding towards zero: d = floor (d / 2)

I don't quite understand the logic yet.
The floor () method returns the floor of x i.e. the largest integer not greater than x. With bitcoin is this the rule to apply, why not the other way around? (the smallest integer)?

Thanks in advance