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984f251fee
The constant MAX_UTF8_PER_UTF16 is used to calculate
required memory when converting from UTF-16 to UTF-8.
If this constant is too big we waste memory.
A code point encoded by one UTF-16 symbol is converted to a
maximum of three UTF-8 symbols, e.g.
0xffff could be encoded as 0xef 0xbf 0xbf.
The first byte carries four bits, the second and third byte
carry six bits each.
A code point encoded by two UTF-16 symbols is converted to four
UTF-8 symbols.
So in this case we need a maximum of two UTF-8 symbols per
UTF-16 symbol.
As the overall maximum is three UTF-8 symobls per UTF-16 symbol
we need MAX_UTF8_PER_UTF16 = 3.
Fixes: 78178bb0c9 lib: add some utf16 handling helpers
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
65 lines
1.8 KiB
C
65 lines
1.8 KiB
C
/*
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* charset conversion utils
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*
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* Copyright (c) 2017 Rob Clark
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*
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* SPDX-License-Identifier: GPL-2.0+
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*/
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#ifndef __CHARSET_H_
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#define __CHARSET_H_
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#define MAX_UTF8_PER_UTF16 3
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/**
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* utf16_strlen() - Get the length of an utf16 string
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*
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* Returns the number of 16 bit characters in an utf16 string, not
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* including the terminating NULL character.
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*
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* @in the string to measure
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* @return the string length
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*/
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size_t utf16_strlen(const uint16_t *in);
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/**
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* utf16_strnlen() - Get the length of a fixed-size utf16 string.
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*
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* Returns the number of 16 bit characters in an utf16 string,
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* not including the terminating NULL character, but at most
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* 'count' number of characters. In doing this, utf16_strnlen()
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* looks at only the first 'count' characters.
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*
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* @in the string to measure
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* @count the maximum number of characters to count
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* @return the string length, up to a maximum of 'count'
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*/
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size_t utf16_strnlen(const uint16_t *in, size_t count);
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/**
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* utf16_strcpy() - UTF16 equivalent of strcpy()
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*/
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uint16_t *utf16_strcpy(uint16_t *dest, const uint16_t *src);
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/**
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* utf16_strdup() - UTF16 equivalent of strdup()
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*/
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uint16_t *utf16_strdup(const uint16_t *s);
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/**
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* utf16_to_utf8() - Convert an utf16 string to utf8
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*
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* Converts 'size' characters of the utf16 string 'src' to utf8
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* written to the 'dest' buffer.
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*
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* NOTE that a single utf16 character can generate up to 3 utf8
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* characters. See MAX_UTF8_PER_UTF16.
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*
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* @dest the destination buffer to write the utf8 characters
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* @src the source utf16 string
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* @size the number of utf16 characters to convert
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* @return the pointer to the first unwritten byte in 'dest'
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*/
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uint8_t *utf16_to_utf8(uint8_t *dest, const uint16_t *src, size_t size);
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#endif /* __CHARSET_H_ */
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