What was r2 supposed to be in scalar static test vectors?

[Coding-Enthusiast]

Scalar has a bunch of static test vectors and there is an r2 value defined in the hard-coded values (bytes) that is never used. What is/was its purpose?

secp256k1/src/tests.c

Line 2927 in 77af1da

secp256k1_scalar_set_b32(&r2, res[i][1], &overflow);

[jonasnick]

r2 was used to test the correctness of scalar_sqr. The tests and scalar_sqr were removed in commit 5437e7bdfbffddf69fdf7b4af7e997c78f5dafbf. You are right that it is unused right now.

I don't know the exact intentions of the tests, but there's also the possibility that the r2 static test vectors also increased test coverage of mul because the removed lines also essentially tested this:

            secp256k1_scalar_mul(&z, &x, &x);
            CHECK(secp256k1_scalar_eq(&r2, &z));

We could either remove r2 and res[i][1] or use them to test mul.

[real-or-random]

We could either remove r2

The quote line secp256k1_scalar_set_b32(&r2, res[i][1], &overflow); also sets overflow, which is checked in the next line. If we removed r2, we would also need to remove that check.

use them to test mul.

Sounds better.