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; * src/composite.c (composition_compute_stop_pos): Add comment.

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Eli Zaretskii 2024-03-04 17:09:29 +02:00
parent ae80192d97
commit 6e801077ae
1 changed files with 21 additions and 5 deletions
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26
src/composite.c
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@ -1153,12 +1153,12 @@ composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
}
else if (charpos > endpos)
{
/* Search backward for a pattern that may be composed and the
position of (possibly) the last character of the match is
/* Search backward for a pattern that may be composed such that
the position of (possibly) the last character of the match is
closest to (but not after) START. The reason for the last
character is that set_iterator_to_next works in reverse order,
and thus we must stop at the last character for composition
check. */
character is that set_iterator_to_next works in reverse
order, and thus we must stop at the last character for
composition check. */
unsigned char *p;
int len;
/* Limit byte position used in fast_looking_at. This is the
@ -1171,6 +1171,22 @@ composition_compute_stop_pos (struct composition_it *cmp_it, ptrdiff_t charpos,
p = SDATA (string) + bytepos;
c = string_char_and_length (p, &len);
limit = bytepos + len;
/* The algorithmic idea behind the loop below is somewhat tricky
and subtle. Keep in mind that any arbitrarily long sequence
of composable characters can potentially be composed to end
at or before START. So the fact that we find a character C
before START that can be composed with several following
characters does not mean we can exit the loop, because some
character before C could also be composed, yielding a longer
composed sequence which ends closer to START. And since a
composition can be arbitrarily long, it is very important to
know where to stop the search back, because the default --
BEGV -- could be VERY far away. Since searching back is only
needed when delivering bidirectional text reordered for
display, and since no character composition can ever cross
into another embedding level, the search could end when it
gets to the end of the current embedding level, but this
limit should be imposed by the caller. */
while (char_composable_p (c))
{
val = CHAR_TABLE_REF (Vcomposition_function_table, c);