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Improve performance of ligature component matching 

This O(N^2) was introduced in 8b2c94c43f.
Make it O(N).
This commit is contained in:
Behdad Esfahbod 2017-10-04 15:06:48 +02:00
parent ab8d70ec70
commit 621c49cb86
1 changed files with 24 additions and 13 deletions
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37
src/hb-ot-layout-gsubgpos-private.hh
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@ -764,6 +764,12 @@ static inline bool match_input (hb_apply_context_t *c,
unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur()); unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur()); unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
enum {
LIGBASE_NOT_CHECKED,
LIGBASE_MAY_NOT_SKIP,
LIGBASE_MAY_SKIP
} ligbase = LIGBASE_NOT_CHECKED;
match_positions[0] = buffer->idx; match_positions[0] = buffer->idx;
for (unsigned int i = 1; i < count; i++) for (unsigned int i = 1; i < count; i++)
{ {
@ -783,29 +789,34 @@ static inline bool match_input (hb_apply_context_t *c,
{ {
/* ...unless, we are attached to a base ligature and that base /* ...unless, we are attached to a base ligature and that base
* ligature is ignorable. */ * ligature is ignorable. */
bool found = false; if (ligbase == LIGBASE_NOT_CHECKED)
const hb_glyph_info_t *out = buffer->out_info;
unsigned int j = buffer->out_len;
while (j && _hb_glyph_info_get_lig_id (&out[j - 1]) == first_lig_id)
{ {
if (_hb_glyph_info_get_lig_comp (&out[j - 1]) == 0) bool found = false;
const hb_glyph_info_t *out = buffer->out_info;
unsigned int j = buffer->out_len;
while (j && _hb_glyph_info_get_lig_id (&out[j - 1]) == first_lig_id)
{ {
if (_hb_glyph_info_get_lig_comp (&out[j - 1]) == 0)
{
j--;
found = true;
break;
}
j--; j--;
found = true;
break;
} }
j--;
if (found && skippy_iter.may_skip (c, out[j]) == hb_apply_context_t::matcher_t::SKIP_YES)
ligbase = LIGBASE_MAY_SKIP;
else
ligbase = LIGBASE_MAY_NOT_SKIP;
} }
if (!found) if (ligbase == LIGBASE_MAY_NOT_SKIP)
return_trace (false);
if (skippy_iter.may_skip (c, out[j]) != hb_apply_context_t::matcher_t::SKIP_YES)
return_trace (false); return_trace (false);
} }
} }
else else
{ {
/* If first component was NOT attached to a previous ligature component, /* If first component was NOT attached to a previous ligature component,
* all subsequent components should also NOT be attached to any ligature * all subsequent components should also NOT be attached to any ligature
* component, unless they are attached to the first component itself! */ * component, unless they are attached to the first component itself! */