Re: compute ISBN-10, char-to-int?

[Emanuel Berg]

tomas wrote:

> It looks a bit roundabout, sure. But how
> would you do it without making any
> assumptions about the underlying encoding?
>
> If you have no scruples, and since chars in
> Emacs Lisp are simply integers, and since
> encoding is almost-UTF-8 which is basically
> ASCII, you could do
>
> (defun char-to-int (c)
>   (- c ?0))
>
> but...
>
>   - it's ugly

Why, I think it's great! New version:
  <https://dataswamp.org/~incal/emacs-init/isbn-new.el>

>   - I don't know if that addresses your
>     question

Me neither... wait, what was my
question exactly?

Yeah, why isn't there a "char-to-int" in
vanilla Emacs already? Should be a pretty
standard thing, right?

> It would be faster, yes. But that will start
> to count once we have ISBN-4294967296 or
> something. By then, you'll have a faster
> computer, too ;-)

... I'm not following? :)

That isn't a valid ISBN-10, the checksum
(check digit) is 3:

  (mod (- 11 (mod (+ (* 4 10)
                     (* 2  9)
                     (* 9  8)
                     (* 4  7)
                     (* 9  6)
                     (* 6  5)
                     (* 7  4)
                     (* 2  3)
                     (* 9  2))
                  11)) 11) ; 3

  (checksum-isbn-10 "4294967296") ; 3

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