bug#7089: 23.2; slow ansi-color-apply

[Stefan Monnier <monnier@iro.umontreal.ca>]

>>> The following version fixed some glitches in setting ansi-color-context.
>>> Also I have received an email from Alex that welcomes the improvement.
>>> Let me know if I should send a patch in.
>> Yes, a patch would be nice.  Also a ChangeLog explaining the change
>> (which should hopefully explain why the new code is faster) would
>> be welcome.

> Attached to the end of this message. I basically rewrite
> ansi-color-apply using re-search-forward (as in
> ansi-color-apply-on-region) which seems to be an order more efficient
> than string-match.

> I have been using the new version in eshell and it is almost as
> efficient as ansi-color-apply-on-region.  It is very painful to use the
> original ansi-color-apply.

Any reason why your new code does something similar to
ansi-color-apply-on-region rather than calling
ansi-color-apply-on-region?

> Do you know for sure string-match is slower (more CPU intensive) than
> re-search-forward?

They should be largely equivalent.  The difference between the two codes
might be due to replace-match and substring.  I.e. the original
ansi-color-apply should be at least as efficient as your code (if not
more) in the case where there are no SGR escape sequences.


        Stefan