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efi_loader: MAX_UTF8_PER_UTF16 = 3

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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>
This commit is contained in:
Heinrich Schuchardt 2017-10-09 21:09:05 +02:00 committed by Alexander Graf
parent 16a73b249d
commit 984f251fee
1 changed files with 2 additions and 2 deletions
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4
include/charset.h
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@ -9,7 +9,7 @@
#ifndef __CHARSET_H_
#define __CHARSET_H_
#define MAX_UTF8_PER_UTF16 4
#define MAX_UTF8_PER_UTF16 3
/**
* utf16_strlen() - Get the length of an utf16 string
@ -52,7 +52,7 @@ uint16_t *utf16_strdup(const uint16_t *s);
* Converts 'size' characters of the utf16 string 'src' to utf8
* written to the 'dest' buffer.
*
* NOTE that a single utf16 character can generate up to 4 utf8
* NOTE that a single utf16 character can generate up to 3 utf8
* characters. See MAX_UTF8_PER_UTF16.
*
* @dest the destination buffer to write the utf8 characters