search

jfbu / texdimens

Utilities and documentation related to TeX dimensional units
1 stars 0 forks source link

0.99b still does not get \texdimenwithunit{dim1}{1pt} right... #6

Closed jfbu closed 2 years ago

jfbu commented 2 years ago

What an embarrassment. I fixed #4 by applying the <1pt branch to =1pt as the former now handled correctly dim1=0pt but this is of course definitely wrong inducing a shift of +1sp. Very stupid.

edit: it was also very stupid before that change when the =1pt case was using the >1pt branch, because this is same math as <1pt albeit implemented differently, and the math is wrong for this special =1pt case...

*\message{\texdimenwithunit{1234sp}{1pt}}
0.01884
*\message{\number\dimexpr0.01884pt}
1235
*\message{\texdimenwithunit{1235sp}{1pt}}
0.01886
*\message{\number\dimexpr0.01886pt}
1236

alas... and I already pushed it to CTAN.

jfbu commented 2 years ago

This is no excuse but this bug was actually already there before my fix to #4. In fact both branches phi<1 and phi>1 use the same mathematical formula, albeit implemented differently to avoid arithmetic overflow for phi<1, but this formula is wrong for phi=1 as it simply induces N-->N+1 at the sp level....

RuixiZhang42 commented 2 years ago

[…] but this formula is wrong for phi=1 as it simply induces N-->N+1 at the sp level....

I noticed this while I was writing the formal proof in the latex3 repo issue. I probably emphasized “formula works if and only if phi>1” way too many times (but apparently not enough, LOL). The reason that the same formula works even when 0<phi<1 is because even if (2T+1)*(psi/2) ends up equal to some other M, which is not necessarily the same N, we can still proceed to floor(M*phi)=floor(N*phi), since phi<1 now serves as a strict contraction.

When phi=1 exactly, the midpoint is exactly half way in between two integers N and N+1, and midpoint+1/2 carries us to N+1, and now we are stuck because floor((N+1)*phi)=floor(N+1)=N+1… Glad this was caught and fixed!

jfbu commented 2 years ago

well, I am a few months older than when creating the package (the \texdimenbothincm is more challenging on all accounts...). And today I tried to do about 4 things distinct at the same time, one of them being texdimens, and initially at dawn, I was only going to produce some pdf doc... then I saw that the \texdimenwithunit from a few days back had an issue, and I ended up doing a bugfix, a bugfix of the bugfix and finally a bugfix of the bugfix of the bugfix.