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Editorial: Add note about hard-coded overflow constrain #3162

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Editorial: Add note about hard-coded overflow constrain #3162

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c3e103c
Add note about hard-coded overflow constrain
sffc Oct 3, 2025
c61e931
Update plaindate.html
sffc Oct 8, 2025
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1 change: 1 addition & 0 deletions spec/plaindate.html
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Expand Up @@ -730,6 +730,7 @@ <h1>
1. If _sign_ × (_d1_ - _isoDate2_.[[Day]]) > 0, return *true*.
1. Return *false*.
</emu-alg>
<emu-note>This operation intentionally uses overflow ~constrain~ when regulating the year-month.</emu-note>
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Is it worth explaining why we use ~constrain~ here?

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I'm not sure I can clearly explain why. It's just a choice we made for how the algorithm works. There are other choices that could have been made.

Do you want to try?

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I suspect that @ptomato may have more recent knowledge than I do about this.

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Well it was actually added by @sffc here: #3138

It's been too long since I read Shane's proof in the comments of that PR, so I don't have context on it anymore.

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Ok, I think the answer is that .until does not know anything about overflow options; only .add accepts such a parameter. As a result, .until returns a duration that subsequently works with .add in overflow constrain mode, but the duration might not work in overflow reject mode.

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I wrote this up. Is it helpful?

</emu-clause>

<emu-clause id="sec-temporal-regulateisodate" type="abstract operation">
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