bug#24603: [RFC 16/18] Refactor character class checking; optimise ASCII case

[Eli Zaretskii <eliz@gnu.org>]

> From: Michal Nazarewicz <mina86@mina86.com>
> Date: Tue,  4 Oct 2016 03:10:39 +0200
> 
> +const unsigned char category_char_bits[] = {
> +  [UNICODE_CATEGORY_UNKNOWN] = 0,
> +  [UNICODE_CATEGORY_Lu] = CHAR_BIT_ALPHA_ | CHAR_BIT_UPPER,
> +  [UNICODE_CATEGORY_Ll] = CHAR_BIT_ALPHA_ | CHAR_BIT_LOWER,

Is this syntax portable enough for us to use it?

> +/* Limited set of character categories which syntax-independent.  Testing of
                                          ^^^^^^^^^^^^^^^^^^^^^^^^
"which are syntax-independent"

> + * those characters do not require any run-time data, e.g. do not depend on
                       ^^^^^^^^^^^^^^                         ^^^^^^^^^^^^^
"does not require" and "does not depend"

Thanks.  I think this change will require a benchmark to make sure we
don't lose too much in terms of performance.