Update EIP-2537: multiplication_cost for G2 update to make it divisible by 1000

[rodiazet]

This PR fixes value of multiplication_cost for G2 which according to comment in the G1/G2 MSM section saying that we want to avoid non-integer arithmetic should be divisible by 1000 the multiplier.
Keeping this as it is now makes the result of the formula depends on the order of multiplications.

[eth-bot]

File EIPS/eip-2537.md

Requires 1 more reviewers from @asanso, @ineffectualproperty, @ralexstokes, @shamatar

[jochem-brouwer]

I might be wrong here, but doesn't the formula: (k * multiplication_cost * discount) / multiplier already explicitly state that the numerator should be calculated first and then thus dividing by the multiplier? The discount numbers are not divisibile by 1000 also (except 1000). I think what is meant with "To avoid non-integer arithmetic" that the formula is not: k * multiplication_cost * discount where discount for example could be (2 multiplications): 0.949 and not 949.

[rodiazet]

yes but even if we calculate (k * multiplication_cost * discount) we cannot be sure that the result will be divisible by 1000. So we can change to make it divisible or add comment that this division must be integer division.

[chfast]

I might be wrong here, but doesn't the formula: (k * multiplication_cost * discount) / multiplier already explicitly state that the numerator should be calculated first and then thus dividing by the multiplier? The discount numbers are not divisibile by 1000 also (except 1000). I think what is meant with "To avoid non-integer arithmetic" that the formula is not: k * multiplication_cost * discount where discount for example could be (2 multiplications): 0.949 and not 949.

Not exactly. If you follow the formula strictly e.g. for G2MSM k=3 you get 62302.5. So you would need to specify that the division in the formula is integer division.

But the spec does the opposite. It says that the constants have been chosen carefully so that the division happens without fractions. However, we haven't read the spec and updated the constants so that this is now in conflict.

If we want to pick the "let's do integer division" path, I'd argue the formula should group constants like this

(multiplication_cost * discount // multiplier) * k