Junio C Hamano <gitster@xxxxxxxxx> writes:
> Teach the hash function and per-line comparison logic to compare lines
> while ignoring the differences in case. It is not an ignore-whitespace
> option but still needs to trigger the inexact match logic, and that is
> why the previous step introduced XDF_INEXACT_MATCH mask.
Nb. how it compares with ignore case in filesystem paths?
> Assign the 7th bit for this option, and move the bits to select diff
> algorithms out of the way in order to leave room for a few bits to add
> more variants of ignore-whitespace, such as --ignore-tab-expansion, if
> somebody else is inclined to do so later.
Or do a proper Unicode sorting / collation algorithm, with different
levels
(4.3 Form a sort key for each string, UTS #10.):
Level 1: alphabetic ordering
Level 2: diacritic ordering
Level 3: case ordering
Level 4: tie-breaking (e.g. in the case when variable is 'shifted')
> We would still need to teach the front-end to flip this bit, for this
> change to be any useful.
>
> Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
> ---
> +static inline int match_a_byte(char ch1, char ch2, long flags)
> +{
> + if (ch1 == ch2)
> + return 1;
> + if (!(flags & XDF_IGNORE_CASE) || ((ch1 | ch2) & 0x80))
> + return 0;
> + if (isupper(ch1))
> + ch1 = tolower(ch1);
> + if (isupper(ch2))
> + ch2 = tolower(ch2);
> + return (ch1 == ch2);
> +}
<del>
Wouldn't a better solution be a collate algorithm rather than changing
a sorting function? Or is it a performance hack on typical body of
text under version control (mainly lowercase)?
</del>
"(libc.info)Collation Fuctions" says:
The functions `strcoll' and `wcscoll' perform this translation
implicitly, in order to do one comparison. By contrast, `strxfrm' and
`wcsxfrm' perform the mapping explicitly. If you are making multiple
comparisons using the same string or set of strings, it is likely to be
more efficient to use `strxfrm' or `wcsxfrm' to transform all the
strings just once, and subsequently compare the transformed strings
with `strcmp' or `wcscmp'.
The function match_a_byte (memcoll?) defined here is similar to strcoll;
do we compare single line with more than one other line?
> +static inline unsigned long hash_a_byte(const char ch_, long flags)
> +{
> + unsigned long ch = ch_ & 0xFF;
> + if ((flags & XDF_IGNORE_CASE) && !(ch & 0x80) && isupper(ch))
> + ch = tolower(ch);
> + return ch;
> +}
> +
Hmmm... hash_a_byte (memxfrm?) is similar to strxfrm, so you do use
one or the other...
--
Jakub Narebski
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