Part of https://github.com/harfbuzz/harfbuzz/issues/3591
"After that, bulk of the time I suppose is spent in binary-searching the
language table. I suggest we split the language table in 2-letter and
3-letter tags, to speed-up the vast majority of cases that are
2-letter."
benchmark-ot, before:
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Benchmark Time CPU Iterations
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BM_hb_ot_tags_from_script_and_language/COMMON zh_CN 112 ns 111 ns 6286271
BM_hb_ot_tags_from_script_and_language/COMMON en_US 60.6 ns 60.4 ns 11671176
BM_hb_ot_tags_from_script_and_language/LATIN en_US 61.3 ns 61.1 ns 11442645
BM_hb_ot_tags_from_script_and_language/COMMON none 4.75 ns 4.74 ns 146997235
BM_hb_ot_tags_from_script_and_language/LATIN none 4.65 ns 4.64 ns 150938747
After:
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Benchmark Time CPU Iterations
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BM_hb_ot_tags_from_script_and_language/COMMON zh_CN 89.5 ns 89.2 ns 7747649
BM_hb_ot_tags_from_script_and_language/COMMON en_US 38.5 ns 38.4 ns 18199432
BM_hb_ot_tags_from_script_and_language/LATIN en_US 39.0 ns 38.9 ns 18049238
BM_hb_ot_tags_from_script_and_language/COMMON none 4.53 ns 4.52 ns 154895110
BM_hb_ot_tags_from_script_and_language/LATIN none 4.54 ns 4.52 ns 154762105
Fixes the following warnings:
hb-ot-tag.cc:330: Warning: HarfBuzz: invalid "allow-none" annotation: only valid for pointer types and out parameters
hb-ot-tag.cc:334: Warning: HarfBuzz: invalid "allow-none" annotation: only valid for pointer types and out parameters
Thanks to David Corbett who revamped our script and language processing
and implemented full BCP 47 support.
https://github.com/harfbuzz/harfbuzz/pull/730
New API:
+hb_ot_layout_table_select_script()
+hb_ot_layout_script_select_language()
+HB_OT_MAX_TAGS_PER_SCRIPT
+HB_OT_MAX_TAGS_PER_LANGUAGE
+hb_ot_tags_from_script_and_language()
+hb_ot_tags_to_script_and_language()
Deprecated API:
-hb_ot_layout_table_choose_script()
-hb_ot_layout_script_find_language()
-hb_ot_tags_from_script()
-hb_ot_tag_from_language()
If the second subtag of a BCP 47 tag is three letters long, it denotes
an extended language. The tag converter ignores the language subtag and
uses the extended language instead.
There are some grandfathered exceptions, which are handled earlier.
The new script, gen-tag-table.py, generates `ot_languages` automatically
from the [OpenType language system tag registry][ot] and the [IANA
Language Subtag Registry][bcp47] with some manual modifications. If an
OpenType tag maps to a BCP 47 macrolanguage, all the macrolanguage's
individual languages are mapped to the same OpenType tag, except for
individual languages with their own OpenType mappings. Deprecated
BCP 47 tags are canonicalized.
[ot]: https://docs.microsoft.com/en-us/typography/opentype/spec/languagetags
[bcp47]: https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
Some OpenType tags correspond to multiple ISO 639 codes. The mapping
from ISO 639 codes lists OpenType tags in priority order, such that more
specific or more likely tags appear first.
Some OpenType tags have no corresponding ISO 639 code in the registry so
their mappings use BCP 47 subtags besides the language. For example, any
BCP 47 tag with a fonipa variant subtag is mapped to 'IPPH', and 'IPPH'
is mapped back to und-fonipa.
Other OpenType tags have no corresponding ISO 639 code because it is not
clear what they are for. HarfBuzz just ignores these tags.
One such ignored tag is 'ZHP ' (Chinese Phonetic). It probably means
zh-Latn. However, it is used in Microsoft JhengHei and Microsoft YaHei
with the script tag 'hani', implying that it is not a romanization
scheme after all. It would be simple enough to add this mapping to
gen-tag-table.py once a definitive mapping is determined.
The manual modifications are mainly either obvious mappings that the
OpenType registry omits or mappings for compatibility with previous
versions of HarfBuzz. Some of the old mappings were discarded, though,
for homophonous language names. For example, OpenType maps 'KUI ' to
kxu; previous versions of HarfBuzz also mapped it to kvd, because kvd
and kxu both happen to be called "Kui".
gen-tag-table.py also generates a function to convert multi-subtag tags
like el-polyton and zh-HK to OpenType tags, replacing `ot_languages_zh`
and the hard-coded list of special cases in `hb_ot_tags_from_language`.
It also generates a function to convert OpenType tags to BCP 47,
replacing the hard-coded list of special cases in
`hb_ot_tag_to_language`.
The old hb-ot-tag.cc functions, `hb_ot_tags_from_script` and
`hb_ot_tag_from_language`, are now wrappers around a new function:
`hb_ot_tags`. It converts a script and a language to arrays of script
tags and language tags. This will make it easier to add new script tags
to scripts, like 'dev3'. It also allows for language fallback chains;
nothing produces more than one language yet though.
Where the old functions return the default tags 'DFLT' and 'dflt',
`hb_ot_tags` returns an empty array. The caller is responsible for
using the default tag in that case.
The new function also adds a new private use subtag syntax for script
overrides: "x-hbscabcd" requests a script tag of 'abcd'.
The old hb-ot-layout.cc functions,`hb_ot_layout_table_choose_script` and
`hb_ot_layout_script_find_language` are now wrappers around the new
functions `hb_ot_layout_table_select_script` and
`hb_ot_layout_script_select_language`. They are essentially the same as
the old ones plus a tag count parameter.
Closes#495.
Behdad Esfahbod
Alexis King
Khaled Hosny
David Corbett
David Corbett
Ebrahim Byagowi
Bruce Mitchener
HinTak
Sascha Brawer