On 04/02/2017 12:09 AM, Andrew Parsloe wrote:
> Is there a simple way to distinguish 0 from 0 in l3fp?
>
> I had been aligning left in a table a column of sines, +0 or 0 followed
> by decimal point & digits. By adding an \hphantom{} before the positive
> numbers, they aligned nicely on the decimal point in the column, but
> then along came 0. The simple conditional, "if !(number < 0) add
> phantom", added the phantom and the column aligned like
> 0
> 0.5878
> 0
> 0.5878
> etc.
> In the absence of formatted printing of numbers, 0 is a problem. Even a
> builtin test for 0 would ease matters, since in any kind of formatted
> printing of numbers 0 and 0 will generally require different handling.
>
> As it is, I've had to test each fp for whether it is zero; if it is I
> convert to a tl variable and test whether that is 0. This is clumsy.
> Hence my opening question.
>
> Andrew
Sorry for the delay.
One option is to normalize 0 to +0 by adding +0. Namely, number+0 is
equal to number for any nonzero number and is +0 for both +0 and 0.
Another option is to compute 1/number after disabling the
"divisionbyzero" trap, and test whether that's +inf or inf, but
that's more complicated than the tl test you're doing.
A better option is that I should add a "copysign" function, that is in
the IEEE standard: copysign(1,x) gives +1 or 1 depending on the sign
bit of x (so in particular this distinguishes +0 and 0).
For your specific use case I would use \fp_to_tl:n then test whether the
first character (\str_head:n) is "" or not. This also covers nan properly.
Bruno
