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Speed up 'find_automatic_composition'

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* src/composite.c (find_automatic_composition): Limit search
backward in buffers to the first newline.  Fix commentary.
This commit is contained in:
Eli Zaretskii 2022-07-10 09:37:40 +03:00
parent 143548fdd6
commit 8dc4c19be8
1 changed files with 29 additions and 17 deletions
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46
src/composite.c
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@ -1513,10 +1513,11 @@ struct position_record
/* Similar to find_composition, but find an automatic composition instead.
This function looks for automatic composition at or near position
POS of OBJECT (a buffer or a string). OBJECT defaults to the
current buffer. It must be assured that POS is not within a static
composition. Also, the current buffer must be displayed in some
window, otherwise the function will return FALSE.
POS of STRING object, either a buffer or a Lisp string. If STRING
is nil, it defaults to the current buffer. It must be assured that
POS is not within a static composition. Also, the current buffer
must be displayed in some window, otherwise the function will
return FALSE.
If LIMIT is negative, and there's no composition that includes POS
(i.e. starts at or before POS and ends at or after POS), return
@ -1525,8 +1526,8 @@ struct position_record
MAX_AUTO_COMPOSITION_LOOKBACK, the maximum number of look-back for
automatic compositions (3) -- this is a limitation imposed by
composition rules in composition-function-table, which see. If
BACKLIM is negative, it stands for the beginning of OBJECT: BEGV
for a buffer or position zero for a string.
BACKLIM is negative, it stands for the beginning of STRING object:
BEGV for a buffer or position zero for a string.
If LIMIT is positive, search for a composition forward (LIMIT >
POS) or backward (LIMIT < POS). In this case, LIMIT bounds the
@ -1535,18 +1536,21 @@ struct position_record
function can find a composition that starts after POS.
BACKLIM limits how far back is the function allowed to look in
OBJECT while trying to find a position where it is safe to start
searching forward for compositions. Such a safe place is generally
the position after a character that can never be composed.
STRING object while trying to find a position where it is safe to
start searching forward for compositions. Such a safe place is
generally the position after a character that can never be
composed.
If BACKLIM is negative, that means the first character position of
OBJECT; this is useful when calling the function for the first time
for a given buffer or string, since it is possible that a
composition begins before POS. However, if POS is very far from
the beginning of OBJECT, a negative value of BACKLIM could make the
function slow. Also, in this case the function may return START
and END that do not include POS, something that is not necessarily
wanted, and needs to be explicitly checked by the caller.
STRING object; this is useful when calling the function for the
first time for a given buffer or string, since it is possible that
a composition begins before POS. However, if POS is very far from
the beginning of STRING object, a negative value of BACKLIM could
make the function slow. For that reason, when STRING is a buffer
or nil, we restrict the search back to the first newline before
POS. Also, in this case the function may return START and END that
do not include POS, something that is not necessarily wanted, and
needs to be explicitly checked by the caller.
When calling the function in a loop for the same buffer/string, the
caller should generally set BACKLIM equal to POS, to avoid costly
@ -1585,7 +1589,15 @@ find_automatic_composition (ptrdiff_t pos, ptrdiff_t limit, ptrdiff_t backlim,
cur.pos = pos;
if (NILP (string))
{
head = backlim < 0 ? BEGV : backlim, tail = ZV, stop = GPT;
if (backlim < 0)
{
/* This assumes a newline can never be composed. */
head = find_newline (pos, -1, 0, -1, -1, NULL, NULL, false) + 1;
}
else
head = backlim;
tail = ZV;
stop = GPT;
cur.pos_byte = CHAR_TO_BYTE (cur.pos);
cur.p = BYTE_POS_ADDR (cur.pos_byte);
}