Commit fe26933c authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Greg Kroah-Hartman
Browse files

vt: add ucs_get_fallback() 



This is the code querying the newly introduced tables.

Signed-off-by: default avatarNicolas Pitre <npitre@baylibre.com>
Link: https://lore.kernel.org/r/20250507141535.40655-7-nico@fluxnic.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent de45d93f

drivers/tty/vt/Makefile

+2 −1
Original line number Diff line number Diff line
@@ -36,7 +36,8 @@ $(obj)/defkeymap.c: $(obj)/%.c: $(src)/%.map 


endif



$(obj)/ucs.o: $(src)/ucs.c $(obj)/ucs_width_table.h $(obj)/ucs_recompose_table.h

$(obj)/ucs.o:	$(src)/ucs.c $(obj)/ucs_width_table.h \

		$(obj)/ucs_recompose_table.h $(obj)/ucs_fallback_table.h



# You may uncomment one of those to have the UCS tables be regenerated

# during the build process. By default the _shipped versions are used.

drivers/tty/vt/ucs.c

+84 −0
Original line number Diff line number Diff line
@@ -157,3 +157,87 @@ u32 ucs_recompose(u32 base, u32 mark) 


	return result ? result->recomposed : 0;

}



/*

 * The fallback table structures implement a 2-level lookup.

 */



struct ucs_page_desc {

	u8 page;	/* Page index (high byte of code points) */

	u8 count;	/* Number of entries in this page */

	u16 start;	/* Start index in entries array */

};



struct ucs_page_entry {

	u8 offset;	/* Offset within page (0-255) */

	u8 fallback;	/* Fallback character or range start marker */

};



#include "ucs_fallback_table.h"



static int ucs_page_desc_cmp(const void *key, const void *element)

{

	u8 page = *(u8 *)key;

	const struct ucs_page_desc *entry = element;



	if (page < entry->page)

		return -1;

	if (page > entry->page)

		return 1;

	return 0;

}



static int ucs_page_entry_cmp(const void *key, const void *element)

{

	u8 offset = *(u8 *)key;

	const struct ucs_page_entry *entry = element;



	if (offset < entry->offset)

		return -1;

	if (entry->fallback == UCS_PAGE_ENTRY_RANGE_MARKER) {

		if (offset > entry[1].offset)

			return 1;

	} else {

		if (offset > entry->offset)

			return 1;

	}

	return 0;

}



/**

 * ucs_get_fallback() - Get a substitution for the provided Unicode character

 * @base: Base Unicode code point (UCS-4)

 *

 * Get a simpler fallback character for the provided Unicode character.

 * This is used for terminal display when corresponding glyph is unavailable.

 * The substitution may not be as good as the actual glyph for the original

 * character but still way more helpful than a squared question mark.

 *

 * Return: Fallback Unicode code point, or 0 if none is available

 */

u32 ucs_get_fallback(u32 cp)

{

	const struct ucs_page_desc *page;

	const struct ucs_page_entry *entry;

	u8 page_idx = cp >> 8, offset = cp;



	if (!UCS_IS_BMP(cp))

		return 0;



	page = __inline_bsearch(&page_idx, ucs_fallback_pages,

				ARRAY_SIZE(ucs_fallback_pages),

				sizeof(*ucs_fallback_pages),

				ucs_page_desc_cmp);

	if (!page)

		return 0;



	entry = __inline_bsearch(&offset, ucs_fallback_entries + page->start,

				 page->count, sizeof(*ucs_fallback_entries),

				 ucs_page_entry_cmp);

	if (!entry)

		return 0;



	if (entry->fallback == UCS_PAGE_ENTRY_RANGE_MARKER)

		entry++;

	return entry->fallback;

}

include/linux/consolemap.h

+6 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ void console_map_init(void); 
bool ucs_is_double_width(uint32_t cp);

bool ucs_is_zero_width(uint32_t cp);

u32 ucs_recompose(u32 base, u32 mark);

u32 ucs_get_fallback(u32 cp);

#else

static inline u16 inverse_translate(const struct vc_data *conp, u16 glyph,

		bool use_unicode)
@@ -75,6 +76,11 @@ static inline u32 ucs_recompose(u32 base, u32 mark) 
{

	return 0;

}



static inline u32 ucs_get_fallback(u32 cp)

{

	return 0;

}

#endif /* CONFIG_CONSOLE_TRANSLATIONS */



#endif /* __LINUX_CONSOLEMAP_H__ */