Etydhv

I'm trying to debug the error in "Dimension too large" error with too many tikzmarks which involves getting a Dimension too large error (duh). I have my suspicions as to what is causing it, and also a suspicion that there will be situations that mean that I can't eliminate the possibility of it occurring altogether.

Is there any way to defend against this error? What I would really like is something like a try ... except ... block. Does that exist?

Here's a MWE to play around with:

documentclassarticle

newdimenad
newdimenbd

ad=16383ptrelax
bd=2ad

showthead
showthebd

begindocument
enddocument

Essentially, I would like to be able to wrap the bd=2ad in something that allows me to define an alternative if it threatens to trigger the dreaded Dimension too large error.

Using l3fp to make a wrapper macro which checks if the dimension exceeds c_max_dim (or maxdimen or 16383.99999pt) and uses a fallback value (which I set to c_max_dim itself) in case the assignment exceeds it:

documentclassarticle
usepackageexpl3
ExplSyntaxOn
cs_new:Npn trydim #1
 
 exp_args:Nf
 __loopspace_try_dim:nn fp_eval:n #1 #1
 
cs_new:Npn __loopspace_try_dim:nn #1 #2
 
 fp_compare:nNnTF abs(#1) > c_max_dim
 
 % Exception code
 dim_use:N c_max_dim
 
 
 % Success code
 % Using dim_eval:n to maintain TeX's behaviour,
 % but you can replace by #1, which is the result of fp_eval:n
 dim_eval:n #2
 
 
ExplSyntaxOff

newdimenad
newdimenbd

ad=trydim16383pt
bd=trydim2ad

showthead
showthebd

begindocument
enddocument

This prints to the terminal:

> 16383.0pt.
l.31 showthead

?
> 16383.99998pt.
l.32 showthebd

?

The "exception code" is what you intend to do if the value exceeds c_max_dim. I used the dim_use:N c_max_dim to get the maximum value possible.

The "success code", you guessed, is when the value is within the allowed range. I used dim_eval:n #2 because there are controversies on the accuracy of l3fp, so the result obeys TeX's rules as long as they are valid. Of course you can change that to fp_eval:n #2 (or, for the matter, #1, which is the fp_eval:n'ed dimension).

Or, if you prefer, an inline fallback value:

documentclassarticle
usepackageexpl3
ExplSyntaxOn
cs_new:Npn trydim #1 #2
 
 exp_args:Nf
 __loopspace_try_dim:nnTF fp_eval:n #1 
 #1 #2
 
prg_new_conditional:Npnn __loopspace_try_dim:nn #1 T, F, TF 
 
 fp_compare:nNnTF abs(#1) > c_max_dim
 prg_return_false: 
 prg_return_true: 
 
ExplSyntaxOff

newdimenad
newdimenbd

ad=trydim16383pt0pt

bd=trydim2ad10pt

showthead
showthebd

begindocument
enddocument

Which prints:

> 16383.0pt.
l.31 showthead

?
> 10.0pt.
l.32 showthebd

?