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/*
** SWISH++
** charsets/utf8.c
**
** Copyright (C) 2002 Paul J. Lucas
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.
**
** This program 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 General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifdef CHARSET_utf8
// local
#include "encoded_char.h"
#include "unicode.h"
//*****************************************************************************
//
// SYNOPSIS
//
encoded_char_range::value_type charset_utf8(
encoded_char_range::pointer /* begin */,
encoded_char_range::pointer &c,
encoded_char_range::pointer end
)
//
// DESCRIPTION
//
// Convert a UTF-8-encoded character sequence to its ASCII equivalent.
//
// PARAMETERS
//
// begin An pointer marking the beginning of the entire encoded range.
//
// c A pointer marking the position of the character to decode.
// It is left after the decoded character.
//
// end A pointer marking the end of the entire encoded range.
//
// RETURN VALUE
//
// Returns the decoded character or ' ' upon error.
//
// SEE ALSO
//
// The Unicode Consortium. "Encoding Forms," The Unicode Standard 3.0,
// section 2.3, Addison-Wesley, 2000.
//
// Francois Yergeau. "RFC 2279: UTF-8, a transformation format of ISO
// 10646," Network Working Group of the Internet Engineering Task Force,
// January 1998.
//
//*****************************************************************************
{
//
// If the byte value is in the ASCII range, we can simply return the
// character.
//
if ( static_cast<unsigned char>( *c ) <= 127u )
return *c++;
//
// Make sure we're at the first byte of the UTF-8 character; if not, "sync"
// by skipping characters until we're at a first byte. Only the first byte
// has the bit pattern 11xxxxxx so it's easy to find.
//
while ( (static_cast<unsigned char>( *c ) & 0xC0u) != 0xC0u ) {
if ( c == end ) {
//
// We ran into "end" before being able to sync: this is weird.
// Return something innocuous like a space since we have to return
// something.
//
return ' ';
}
++c;
}
if ( (static_cast<unsigned char>( *c ) & 0xFEu) == 0xFEu ) {
//
// The octets FE and FF are explicity forbidden: skip over the
// offending byte and return something innocuous like a space since we
// have to return something.
//
++c;
return ' ';
}
//
// Using a static table to know how many bytes are in the UTF-8 character
// is the fastest way.
//
static char const trailing_bytes_table[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // C0-CF
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // D0-DF
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // E0-EF
3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, // F0-FF
};
int const trailing_bytes = trailing_bytes_table[
static_cast<unsigned char>( *c )
];
register ucs4 u = 0;
switch ( trailing_bytes ) {
case 5: u += static_cast<unsigned char>( *c++ ); u <<= 6;
if ( c == end ) break;
case 4: u += static_cast<unsigned char>( *c++ ); u <<= 6;
if ( c == end ) break;
case 3: u += static_cast<unsigned char>( *c++ ); u <<= 6;
if ( c == end ) break;
case 2: u += static_cast<unsigned char>( *c++ ); u <<= 6;
if ( c == end ) break;
case 1: u += static_cast<unsigned char>( *c++ ); u <<= 6;
if ( c == end ) break;
case 0: u += static_cast<unsigned char>( *c++ );
}
static unsigned long const offset_table[] = {
0x0u, 0x3080u, 0xE2080u, 0x3C82080u, 0xFA082080u, 0x82082080u
};
u -= offset_table[ trailing_bytes ];
return unicode_to_ascii( u );
}
#endif /* CHARSET_utf8 */
/* vim:set et sw=4 ts=4: */
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