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sortix--sortix/libc/wchar/wcrtomb.cpp
2014-02-06 00:15:03 +01:00

80 lines
2.5 KiB
C++

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2012.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
wchar/wcrtomb.cpp
Convert a wide character to a multibyte sequence.
*******************************************************************************/
#include <errno.h>
#include <stdint.h>
#include <wchar.h>
extern "C"
size_t wcrtomb(char* restrict s, wchar_t wc, mbstate_t* restrict /*ps*/)
{
if ( !wc )
{
if ( s )
*s = '\0';
return 1;
}
uint32_t unicode = wc;
uint8_t* buf = (uint8_t*) s;
unsigned bytes = 1;
unsigned bits = 7;
if ( (1U<<7U) <= unicode ) { bytes = 2; bits = 11; }
if ( (1U<<11U) <= unicode ) { bytes = 3; bits = 16; }
if ( (1U<<16U) <= unicode ) { bytes = 4; bits = 21; }
if ( (1U<<21U) <= unicode ) { bytes = 5; bits = 26; }
if ( (1U<<26U) <= unicode ) { bytes = 6; bits = 31; }
if ( (1U<<31U) <= unicode ) { errno = EILSEQ; return (size_t) -1; }
if ( !s )
return bytes;
uint8_t prefix;
unsigned prefixavai;
switch ( bytes )
{
case 1: prefixavai = 7; prefix = 0b0U << prefixavai; break;
case 2: prefixavai = 5; prefix = 0b110U << prefixavai; break;
case 3: prefixavai = 4; prefix = 0b1110U << prefixavai; break;
case 4: prefixavai = 3; prefix = 0b11110U << prefixavai; break;
case 5: prefixavai = 2; prefix = 0b111110U << prefixavai; break;
case 6: prefixavai = 1; prefix = 0b1111110U << prefixavai; break;
default: __builtin_unreachable();
}
// Put the first bits in the unused area of the prefix.
prefix |= unicode >> (bits - prefixavai);
*buf++ = prefix;
unsigned bitsleft = bits - prefixavai;
while ( bitsleft )
{
bitsleft -= 6;
uint8_t elembits = (unicode>>bitsleft) & ((1U<<6U)-1U);
uint8_t elem = (0b10U<<6U) | elembits;
*buf++ = elem;
}
return bytes;
}