8000 Avoid slices in entries of decomposition tables by glandium · Pull Request #86 · unicode-rs/unicode-normalization · GitHub
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Avoid slices in entries of decomposition tables #86

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Jun 23, 2022
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Avoid slices in entries of decomposition tables #86

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16 changes: 13 additions & 3 deletions scripts/unicode.py
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Original file line number Diff line number Diff line change
Expand Up @@ -391,9 +391,19 @@ def gen_composition_table(canon_comp, out):
def gen_decomposition_tables(canon_decomp, compat_decomp, cjk_compat_variants_decomp, out):
tables = [(canon_decomp, 'canonical'), (compat_decomp, 'compatibility'), (cjk_compat_variants_decomp, 'cjk_compat_variants')]
for table, name in tables:
gen_mph_data(name + '_decomposed', table, "(u32, &'static [char])",
lambda k: "(0x{:x}, &[{}])".format(k,
", ".join("'\\u{%s}'" % hexify(c) for c in table[k])))
offsets = {}
offset = 0
out.write("pub(crate) const %s_DECOMPOSED_CHARS: &[char] = &[\n" % name.upper())
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Wouldn't a fixed array avoid the relocations altogether? As in, a %s_DECOMPOSED_CHARS: [char; _] = or so?

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@glandium glandium Jun 24, 2022 •
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The tables are const. The slice for the table themselves are not stored in .data.rel.ro at all because of that. So there are actually no relocations for those (also, that would only be one per table, which is not as dramatic as one per entry).

for k, v in table.items():
offsets[k] = offset
offset += len(v)
for c in v:
out.write(" '\\u{%s}',\n" % hexify(c))
# The largest offset must fit in a u16.
assert offset < 65536
out.write("];\n")
gen_mph_data(name + '_decomposed', table, "(u32, (u16, u16))",
lambda k: "(0x{:x}, ({}, {}))".format(k, offsets[k], len(table[k])))

def gen_qc_match(prop_table, out):
out.write(" match c {\n")
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3 changes: 3 additions & 0 deletions src/lookups.rs
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Expand Up @@ -51,6 +51,7 @@ pub(crate) fn canonical_fully_decomposed(c: char) -> Option<&'static [char]> {
pair_lookup_fv_opt,
None,
)
.map(|(start, len)| &CANONICAL_DECOMPOSED_CHARS[start as usize..][..len as usize])
}

pub(crate) fn compatibility_fully_decomposed(c: char) -> Option<&'static [char]> {
Expand All @@ -62,6 +63,7 @@ pub(crate) fn compatibility_fully_decomposed(c: char) -> Option<&'static [char]>
pair_lookup_fv_opt,
None,
)
.map(|(start, len)| &COMPATIBILITY_DECOMPOSED_CHARS[start as usize..][..len as usize])
}

pub(crate) fn cjk_compat_variants_fully_decomposed(c: char) -> Option<&'static [char]> {
Expand All @@ -73,6 +75,7 @@ pub(crate) fn cjk_compat_variants_fully_decomposed(c: char) -> Option<&'static [
pair_lookup_fv_opt,
None,
)
.map(|(start, len)| &CJK_COMPAT_VARIANTS_DECOMPOSED_CHARS[start as usize..][..len as usize])
}

/// Return whether the given character is a combining mark (`General_Category=Mark`)
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