Add ecMulG2 precompile

[ColoCarletti]

Description

This pull request introduces a precompile for efficiently computing scalar multiplication of a point on the D-type sextic twist of the BN254 curve over Fp2. The curve is defined by the equation:

$E' : y^2 = x^3 + (19485874751759354771024239261021720505790618469301721065564631296452457478373 + 266929791119991161246907387137283842545076965332900288569378510910307636690 u)$

The addition operation involves a point where each coordinate $(X, Y)$ is represented as elements of Fp2 and a sacalar $k$.

For example:

$A = ( X, Y)$

Where:

$X = (aX_0 + aX_1 * u)$
$Y = (aY_0 + aY_1 * u)$

The calldata expects input parameters:

$aX_0,aX_1,aY_0,aY_1,k$

And returns:

$cX_0,cX_1,cY_0,cY_1$

Test

First run the local node

make run-node

Once the node us up run:

make test PRECOMPILE=ecmul_g2

[fkrause98]

Some tests are failing for me, I've double checked cloning from zero and trying to run them,
maybe there are some files without commiting?

cd tests && \
cargo test ecmul_g2

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 36 filtered out; finished in 0.00s


running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 196 filtered out; finished in 0.00s


running 10 tests
test ecmul_g2_p_times_two_is_2p ... FAILED
test ecmul_g2_p_infinity_times_0_is_infinity ... FAILED
test ecmul_g2_p_infinity_times_k_is_infinity ... FAILED
test ecmul_g2_p_times_one_is_p ... FAILED
test ecmul_g2_valid_1 ... FAILED
test ecmul_g2_invalid_p_not_in_curve ... ok
test ecmul_g2_p_times_zero_is_infinity ... FAILED
test ecmul_g2_valid_2 ... FAILED
test ecmul_g2_valid_3 ... FAILED
test ecmul_g2_coordinates_not_in_field ... ok

failures:

---- ecmul_g2_p_times_two_is_2p stdout ----
thread 'ecmul_g2_p_times_two_is_2p' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- ecmul_g2_p_infinity_times_0_is_infinity stdout ----
thread 'ecmul_g2_p_infinity_times_0_is_infinity' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_p_infinity_times_k_is_infinity stdout ----
thread 'ecmul_g2_p_infinity_times_k_is_infinity' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_p_times_one_is_p stdout ----
thread 'ecmul_g2_p_times_one_is_p' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_valid_1 stdout ----
thread 'ecmul_g2_valid_1' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_p_times_zero_is_infinity stdout ----
thread 'ecmul_g2_p_times_zero_is_infinity' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_valid_2 stdout ----
thread 'ecmul_g2_valid_2' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ecmul_g2_valid_3 stdout ----
thread 'ecmul_g2_valid_3' panicked at tests/test_utils.rs:40:10:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }


failures:
    ecmul_g2_p_infinity_times_0_is_infinity
    ecmul_g2_p_infinity_times_k_is_infinity
    ecmul_g2_p_times_one_is_p
    ecmul_g2_p_times_two_is_2p
    ecmul_g2_p_times_zero_is_infinity
    ecmul_g2_valid_1
    ecmul_g2_valid_2
    ecmul_g2_valid_3

test result: FAILED. 2 passed; 8 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.12s

[fkrause98]

LGTM!

[IAvecilla]

Can we change this unwrap in the test_utils file:

fn write_line_to_report(used_gas: u32, report_to_write: &str) {
    let mut file = OpenOptions::new()
        .append(true)
        .open(report_to_write)
        .unwrap()
        ...
}

to something like:

fn write_line_to_report(used_gas: u32, report_to_write: &str) {
    let mut file = OpenOptions::new()
        .append(true)
        .open(report_to_write)
        .expect(&format!("Unable to write the gas report in {report_to_write:?}"));
        ...
}

Just to better indicate that the error happens in the gas reports generation and make it easier to understand.
In the future we should pass the test besides the failure on writing the report