ecmult: fix definition of STRAUSS_SCRATCH_OBJECTS

[jonasnick]

This bug was introduced in 7506e06 by adding
an allocation but not updating the constant.

[real-or-random]

Good to move this to a separate PR.

Unfortunately the constants are highly coupled with the allocation code. Can you add a comment to the allocation code that says that the constant must be updated when this is changed (also for pippenger)? Otherwise I bet we'll get this wrong again in the future.

[robot-dreams]

Thanks for catching this. Looks good to me—I confirmed that:

• secp256k1_ecmult_strauss_batch now has 7 calls to secp256k1_scratch_alloc instead of 6
• What matters for STRAUSS_SCRATCH_OBJECTS is the number of allocations (not the total size being allocated), since it's used to account for per-allocation alignment padding

I agree with @real-or-random 's suggestion. In addition, do the functions secp256k1_strauss_scratch_size and secp256k1_pippenger_scratch_size also need to be kept in sync when allocations are updated?

[jonasnick]

Good idea. Added comments.

[real-or-random]

ACK 60bf889

[real-or-random]

@robot-dreams Want give a final review here?

[robot-dreams]

ACK 60bf889