Change value for short path to return zero in wadExp

[engn33r]

Description

This is the same optimization described in pcaversaccio/snekmate#189

This PR is for a very small optimization that is possible by increasing the range of values that will take the short logic path of wadExp() and return zero. I am not sure how the previously chosen value of -42139678854452767551 was selected, but these tests demonstrate the actual turning point when the result of the current wadExp() implementation transitions from 1 to zero.

  function testWadExpZeroPoint() public {
      assertEq(wadExp(-41446531673892822312), 1);
      assertEq(wadExp(-41446531673892822313), 0);
  }

The change to CREATE3.t.sol is from the linter, not a change I deliberately made.

Checklist

Ensure you completed all of the steps below before submitting your pull request:

• Ran forge snapshot?
• Ran npm run lint?
• Ran forge test?

Pull requests with an incomplete checklist will be thrown out.

[transmissions11]

interesting, nice find!

cc @recmo — want to double check, does this look right to you?

[engn33r]

For reference, you can get this value in python (minus some precision) with numpy.log(10**-18)

[recmo]

This is where the original value came from: https://twitter.com/recmo/status/1744470975872127005

The rational approximation may go from 0 to 1 earlier or later than this exact value.
A) If it is earlier, then using the ideal value improves accuracy and performance.
B) If it is later, than we can raise the value without changing the output which increases efficiency for a small range of inputs.

Your unit tests seems to show B is the case, so it should be save to raise the limit. (Which means a smaller absolute value since it is negative.)

(But this assumes that the rational approximation is monotonic, i.e. that it only transitions from 0 to 1 once. I did some empirical testing of this, but it is not exhaustive. So there is a very small chance that with this extra optimization it will now return 0 where it previously returned the more accurately rounded value of 1.)