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55 lines (49 loc) · 3 KB
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// Simple functions to test UTF-8 characters.
// Copyright (C)2010 Francois-R.Boyer@PolyMtl.ca
// First version 2010-08
//
// Written for notepad++, and distributed under same license:
// 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.
namespace Utf8 { // could be a static class, instead of a namespace, if it needs private members
// basic classification of UTF-8 bytes
inline static bool isSingleByte(UCHAR c) { return c < 0x80; }
inline static bool isPartOfMultibyte(UCHAR c) { return c >= 0x80; }
inline static bool isFirstOfMultibyte(UCHAR c) { return c >= 0xC2 && c < 0xF5; } // 0xF5 to 0xFD are defined by UTF-8, but are not currently valid Unicode
inline static bool isContinuation(UCHAR c) { return (c & 0xC0) == 0x80; }
inline static bool isValid(UCHAR c) { return c < 0xC0 || isFirstOfMultibyte(c); } // validates a byte, out of context
// number of continuation bytes for a given valid first character (0 for single byte characters)
inline static int continuationBytes(UCHAR c) {
static const char _len[] = { 1,1,2,3 };
return (c < 0xC0) ? 0 : _len[(c & 0x30) >> 4];
}
// validates a full character
inline static bool isValid(const char* buf, int buflen) {
if(isSingleByte(buf[0])) return true; // single byte is valid
if(!isFirstOfMultibyte(buf[0])) return false; // not single byte, nor valid multi-byte first byte
int charContinuationBytes = continuationBytes(buf[0]);
if(buflen < charContinuationBytes+1) return false; // character does not fit in buffer
for(int i = charContinuationBytes; i>0; --i)
if(!isContinuation(*(++buf))) return false; // not enough continuation bytes
return true; // the character is valid (if there are too many continuation bytes, it is the next character that will be invalid)
}
// rewinds to the first byte of a multi-byte character for any valid UTF-8 (and will not rewind too much on any other input)
inline static int characterStart(const char* buf, int startingIndex) {
int charContinuationBytes = 0;
while(charContinuationBytes < startingIndex // rewind past start of buffer?
&& charContinuationBytes < 5 // UTF-8 support up to 5 continuation bytes (but valid sequences currently do not have more than 3)
&& isContinuation(buf[startingIndex-charContinuationBytes])
)
++charContinuationBytes;
return startingIndex-charContinuationBytes;
}
};