sortix--sortix/libc/wchar/wcrtomb.cpp

/*******************************************************************************

    Copyright(C) Jonas 'Sortie' Termansen 2012, 2014.

    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 <stdlib.h>
#include <wchar.h>

static
size_t utf8_wcrtomb(char* restrict s, wchar_t wc, mbstate_t* restrict /*ps*/)
{
	// The definition of UTF-8 prohibits encoding character numbers between
	// U+D800 and U+DFFF, which are reserved for use with the UTF-16 encoding
	// form (as surrogate pairs) and do not directly represent characters.
	if ( 0xD800 <= wc && wc <= 0xDFFF )
		return errno = EILSEQ, (size_t) -1;

	// RFC 3629 limits UTF-8 to 0x0 through 0x10FFFF.
	if ( 0x10FFFF <= wc )
		return errno = EILSEQ, (size_t) -1;

	size_t index = 0;

	if ( wc < (1 << (7)) )  /* 0xxxxxxx */
	{
		s[index++] = 0b00000000 | (wc >> 0 & 0b01111111);
		return index;
	}

	if ( wc < (1 << (5 + 1 * 6)) )  /* 110xxxxx 10xxxxxx^1 */
	{
		s[index++] = 0b11000000 | (wc >> 6 & 0b00011111);
		s[index++] = 0b10000000 | (wc >> 0 & 0b00111111);
		return index;
	}

	if ( wc < (1 << (4 + 2 * 6)) )  /* 1110xxxx 10xxxxxx^2 */
	{
		s[index++] = 0b11100000 | (wc >> 2*6 & 0b00001111);
		s[index++] = 0b10000000 | (wc >> 1*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 0*6 & 0b00111111);
		return index;
	}

	if ( wc < (1 << (3 + 3 * 6)) )  /* 11110xxx 10xxxxxx^3 */
	{
		s[index++] = 0b11110000 | (wc >> 3*6 & 0b00000111);
		s[index++] = 0b10000000 | (wc >> 2*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 1*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 0*6 & 0b00111111);
		return index;
	}

#if 0 /* 5-byte and 6-byte sequences are forbidden by RFC 3629 */
	if ( wc < (1 << (2 + 4 * 6)) )  /* 111110xx 10xxxxxx^4 */
	{
		s[index++] = 0b11111000 | (wc >> 4*6 & 0b00000011);
		s[index++] = 0b10000000 | (wc >> 3*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 2*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 1*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 0*6 & 0b00111111);
		return index;
	}

	if ( wc < (1 << (1 + 5 * 6)) )  /* 111110xx 10xxxxxx^5 */
	{
		s[index++] = 0b11111100 | (wc >> 5*6 & 0b00000001);
		s[index++] = 0b10000000 | (wc >> 4*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 3*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 2*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 1*6 & 0b00111111);
		s[index++] = 0b10000000 | (wc >> 0*6 & 0b00111111);
		return index;
	}
#endif

	return errno = EILSEQ; return (size_t) -1;
}

extern "C"
size_t wcrtomb(char* restrict s, wchar_t wc, mbstate_t* restrict ps)
{
	char internal_buffer[MB_CUR_MAX];
	if ( !s )
		wc = L'\0', s = internal_buffer;

	// TODO: Verify whether the current locale is UTF-8.
	return utf8_wcrtomb(s, wc, ps);
}