linux-next.git/drivers/tty/vt/gen_ucs_width_table.py, branch master

vt: merge ucs_is_zero_width()/ucs_is_double_width() into ucs_get_width()

2026-05-22T09:47:33+00:00

The hot path in vc_process_ucs() asks two independent questions about the same code point -- "is it double-width?" and "is it zero-width?" -- and was answering each with its own bsearch over its own table. For anything past the leading bounds check that meant two scans of the BMP width tables back to back for what is logically a single lookup. Replace both with one ucs_get_width(cp) returning 0, 1, or 2 in a single bsearch, while keeping the total table footprint at the same 2384 B as before. To do so, merge the zero-width and double-width ranges per region into one sorted-by-`first` table. BMP entries stay 4 bytes; per-entry width is hosted in spare bits of the non-BMP table's `last` field. Non-BMP code points use only 20 of 32 bits, so each u32 has 12 unused high bits. Store first/last shifted left by 12 and use the low 12 bits of `last` for metadata: bit 11 is this entry's own width flag, bits 0..7 host an 8-bit chunk of the BMP double-width bitmap. Because the metadata bits sit strictly below the lowest cp-scale bit, the bsearch comparator remains a plain u32 compare on shifted keys with no masking. In vc_process_ucs() the overwhelmingly common single-width path now collapses to a single predicted branch: if (likely(w == 1)) return 1; Note: scripts/checkpatch.pl complains about "Macros with complex values should be enclosed in parentheses" for the BMP_*WIDTH and RANGE_*WIDTH macros. They are deliberately defined to expand to a comma-separated (first, last) pair so they can populate the two adjacent fields of a struct initializer; wrapping them in parentheses would turn that into a comma-expression and defeat the whole construction. Please ignore. Signed-off-by: Nicolas Pitre Link: https://patch.msgid.link/20260515034857.2514225-1-nico@fluxnic.net Signed-off-by: Greg Kroah-Hartman

vt: move UCS tables to the "shipped" form

2025-04-26T09:22:04+00:00

Use the "shipped" mechanism to copy pre-generated tables to the build tree by default. If GENERATE_UCS_TABLES=1 then they are generated at build time instead. If GENERATE_UCS_TABLES=2 then gen_ucs_recompose_table.py is invoked with --full. Signed-off-by: Nicolas Pitre Suggested-by: Jiri Slaby Link: https://lore.kernel.org/r/20250417184849.475581-15-nico@fluxnic.net Signed-off-by: Greg Kroah-Hartman

vt: update gen_ucs_width_table.py to make tables more space efficient

2025-04-26T09:22:04+00:00

Split table ranges into BMP (16-bit) and non-BMP (above 16-bit). This reduces the corresponding text size by 20-25%. Signed-off-by: Nicolas Pitre Reviewed-by: Jiri Slaby Link: https://lore.kernel.org/r/20250417184849.475581-13-nico@fluxnic.net Signed-off-by: Greg Kroah-Hartman

vt: introduce gen_ucs_width_table.py to create ucs_width_table.h

2025-04-26T09:22:03+00:00

The table in ucs.c is terribly out of date and incomplete. We also need a second table to store zero-width code points. Properly maintaining those tables manually is impossible. So here's a script to generate them. Signed-off-by: Nicolas Pitre Reviewed-by: Jiri Slaby Link: https://lore.kernel.org/r/20250417184849.475581-5-nico@fluxnic.net Signed-off-by: Greg Kroah-Hartman