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[set] Optimize non-const page_for() using last_page_lookup caching 

This speeds up SetOrderedInsert tests by 15 to 40 percent, and the
subset_mplus1p benchmarks by 9 to 27 percent.
This commit is contained in:
Behdad Esfahbod 2022-04-29 12:45:48 -06:00
parent dd005911b9
commit c283e41ce3
1 changed files with 15 additions and 1 deletions
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16
src/hb-bit-set.hh
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@ -874,7 +874,19 @@ struct hb_bit_set_t
page_t *page_for (hb_codepoint_t g, bool insert = false)
{
page_map_t map = {get_major (g), pages.length};
unsigned major = get_major (g);
/* The extra page_map length is necessary; can't just rely on vector here,
* since the next check would be tricked because a null page also has
* major==0, which we can't distinguish from an actualy major==0 page... */
if (likely (last_page_lookup < page_map.length))
{
auto &cached_page = page_map.arrayZ[last_page_lookup];
if (cached_page.major == major)
return &pages[cached_page.index];
}
page_map_t map = {major, pages.length};
unsigned int i;
if (!page_map.bfind (map, &i, HB_NOT_FOUND_STORE_CLOSEST))
{
@ -890,6 +902,8 @@ struct hb_bit_set_t
(page_map.length - 1 - i) * page_map.item_size);
page_map[i] = map;
}
last_page_lookup = i;
return &pages[page_map[i].index];
}
const page_t *page_for (hb_codepoint_t g) const