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LibUnicode: Optimize the canonical composition algorithm implementation

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It now takes O(N) time instead of O(N^2) time. Additionally some always
false conditions are removed.
This commit is contained in:
Idan Horowitz
2024-04-06 17:28:17 +03:00
committed by Tim Flynn
parent 6207405f3d
commit e227bf0f71
1 changed files with 32 additions and 22 deletions
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54
Userland/Libraries/LibUnicode/Normalize.cpp
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@@ -208,11 +208,11 @@ static void canonical_ordering_algorithm(Span<u32> code_points)
// See Section 3.11, D115 of Version 15.0.0 of the Unicode Standard.
static bool is_blocked(Span<u32> code_points, size_t a, size_t c)
{
if (!is_starter(code_points[a]) || a == c - 1)
if (a == c - 1)
return false;
auto const c_combining_class = Unicode::canonical_combining_class(code_points[c]);
auto const b_combining_class = Unicode::canonical_combining_class(code_points[c - 1]);
return b_combining_class == 0 || b_combining_class >= c_combining_class;
return b_combining_class >= c_combining_class;
}
// The Canonical Composition Algorithm, as specified in Version 15.0.0 of the Unicode Standard.
@@ -220,30 +220,40 @@ static bool is_blocked(Span<u32> code_points, size_t a, size_t c)
// https://www.unicode.org/versions/Unicode15.0.0/ch03.pdf#G50628
static void canonical_composition_algorithm(Vector<u32>& code_points)
{
if (code_points.size() <= 1)
return;
ssize_t last_starter = is_starter(code_points[0]) ? 0 : -1;
for (size_t i = 1; i < code_points.size(); ++i) {
auto const current_character = code_points[i];
// R1. Seek back (left) to find the last Starter L preceding C in the character sequence
for (ssize_t j = i - 1; j >= 0; --j) {
if (!is_starter(code_points[j]))
continue;
// R2. If there is such an L, and C is not blocked from L,
// and there exists a Primary Composite P which is canonically equivalent to <L, C>,
// then replace L by P in the sequence and delete C from the sequence.
if (is_blocked(code_points.span(), j, i))
continue;
auto composite = combine_hangul_code_points(code_points[j], current_character);
if (composite == 0)
composite = combine_code_points(code_points[j], current_character);
if (composite != 0) {
code_points[j] = composite;
code_points.remove(i);
--i;
break;
}
if (last_starter == -1) {
if (is_starter(current_character))
last_starter = i;
continue;
}
// R2. If there is such an L, and C is not blocked from L,
// and there exists a Primary Composite P which is canonically equivalent to <L, C>,
// then replace L by P in the sequence and delete C from the sequence.
if (is_blocked(code_points.span(), last_starter, i)) {
if (is_starter(current_character))
last_starter = i;
continue;
}
auto composite = combine_hangul_code_points(code_points[last_starter], current_character);
if (composite == 0)
composite = combine_code_points(code_points[last_starter], current_character);
if (composite == 0) {
if (is_starter(current_character))
last_starter = i;
continue;
}
code_points[last_starter] = composite;
code_points.remove(i);
--i;
}
}