* src/marker.c: Try and speed up byte<->char conversion with many markers.
When considering markers (to find a starting point for the conversion), typically one of the two bounds is nearby (coming from cached_(byte|char)pos) but the other is far (point-min or point-max), so change the exit condition so we stop as soon as *one* of the bounds is near. (BYTECHAR_DISTANCE_INITIAL, BYTECHAR_DISTANCE_INCREMENT): New constants. (buf_charpos_to_bytepos, buf_bytepos_to_charpos): Use them to try and reduce the number of markers we consider.
This commit is contained in:
Stefan Monnier
parent
9c1176247b
commit
b300052fb4
1 changed files with 40 additions and 10 deletions
50
src/marker.c
50
src/marker.c
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@ -90,7 +90,7 @@ clear_charpos_cache (struct buffer *b)
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#define CONSIDER(CHARPOS, BYTEPOS) \
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{ \
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ptrdiff_t this_charpos = (CHARPOS); \
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bool changed = 0; \
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bool changed = false; \
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\
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if (this_charpos == charpos) \
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{ \
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@ -105,14 +105,14 @@ clear_charpos_cache (struct buffer *b)
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{ \
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best_above = this_charpos; \
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best_above_byte = (BYTEPOS); \
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changed = 1; \
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changed = true; \
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} \
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} \
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else if (this_charpos > best_below) \
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{ \
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best_below = this_charpos; \
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best_below_byte = (BYTEPOS); \
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changed = 1; \
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changed = true; \
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} \
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\
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if (changed) \
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@ -133,6 +133,28 @@ CHECK_MARKER (Lisp_Object x)
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CHECK_TYPE (MARKERP (x), Qmarkerp, x);
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}
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/* When converting bytes from/to chars, we look through the list of
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markers to try and find a good starting point (since markers keep
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track of both bytepos and charpos at the same time).
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But if there are many markers, it can take too much time to find a "good"
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marker from which to start. Worse yet: if it takes a long time and we end
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up finding a nearby markers, we won't add a new marker to cache this
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result, so next time around we'll have to go through this same long list
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to (re)find this best marker. So the further down the list of
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markers we go, the less demanding we are w.r.t what is a good marker.
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The previous code used INITIAL=50 and INCREMENT=0 and this lead to
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really poor performance when there are many markers.
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I haven't tried to tweak INITIAL, but experiments on my trusty Thinkpad
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T61 using various artificial test cases seem to suggest that INCREMENT=50
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might be "the best compromise": it significantly improved the
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worst case and it was rarely slower and never by much.
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The asymptotic behavior is still poor, tho, so in largish buffers with many
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overlays (e.g. 300KB and 30K overlays), it can still be a bottlneck. */
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#define BYTECHAR_DISTANCE_INITIAL 50
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#define BYTECHAR_DISTANCE_INCREMENT 50
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/* Return the byte position corresponding to CHARPOS in B. */
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ptrdiff_t
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@ -141,6 +163,7 @@ buf_charpos_to_bytepos (struct buffer *b, ptrdiff_t charpos)
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struct Lisp_Marker *tail;
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ptrdiff_t best_above, best_above_byte;
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ptrdiff_t best_below, best_below_byte;
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ptrdiff_t distance = BYTECHAR_DISTANCE_INITIAL;
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eassert (BUF_BEG (b) <= charpos && charpos <= BUF_Z (b));
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@ -180,8 +203,11 @@ buf_charpos_to_bytepos (struct buffer *b, ptrdiff_t charpos)
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/* If we are down to a range of 50 chars,
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don't bother checking any other markers;
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scan the intervening chars directly now. */
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if (best_above - best_below < 50)
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if (best_above - charpos < distance
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|| charpos - best_below < distance)
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break;
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else
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distance += BYTECHAR_DISTANCE_INCREMENT;
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}
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/* We get here if we did not exactly hit one of the known places.
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@ -248,7 +274,7 @@ buf_charpos_to_bytepos (struct buffer *b, ptrdiff_t charpos)
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#define CONSIDER(BYTEPOS, CHARPOS) \
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{ \
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ptrdiff_t this_bytepos = (BYTEPOS); \
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int changed = 0; \
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int changed = false; \
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\
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if (this_bytepos == bytepos) \
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{ \
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@ -263,14 +289,14 @@ buf_charpos_to_bytepos (struct buffer *b, ptrdiff_t charpos)
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{ \
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best_above = (CHARPOS); \
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best_above_byte = this_bytepos; \
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changed = 1; \
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changed = true; \
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} \
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} \
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else if (this_bytepos > best_below_byte) \
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{ \
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best_below = (CHARPOS); \
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best_below_byte = this_bytepos; \
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changed = 1; \
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changed = true; \
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} \
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\
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if (changed) \
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@ -293,6 +319,7 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
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struct Lisp_Marker *tail;
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ptrdiff_t best_above, best_above_byte;
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ptrdiff_t best_below, best_below_byte;
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ptrdiff_t distance = BYTECHAR_DISTANCE_INITIAL;
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eassert (BUF_BEG_BYTE (b) <= bytepos && bytepos <= BUF_Z_BYTE (b));
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@ -323,8 +350,11 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
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/* If we are down to a range of 50 chars,
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don't bother checking any other markers;
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scan the intervening chars directly now. */
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if (best_above - best_below < 50)
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if (best_above - bytepos < distance
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|| bytepos - best_below < distance)
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break;
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else
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distance += BYTECHAR_DISTANCE_INCREMENT;
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}
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/* We get here if we did not exactly hit one of the known places.
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@ -744,8 +774,8 @@ count_markers (struct buffer *buf)
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ptrdiff_t
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verify_bytepos (ptrdiff_t charpos)
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{
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ptrdiff_t below = 1;
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ptrdiff_t below_byte = 1;
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ptrdiff_t below = BEG;
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ptrdiff_t below_byte = BYTE_BEG;
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while (below != charpos)
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{
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