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uemacs/utf8.c

156 lines
3.7 KiB
C

/* utf8.c -- implements utf8.h, converts between unicode and UTF-8 */
#define _XOPEN_SOURCE /* wcwidth in wchar.h */
#include "utf8.h"
#include <assert.h>
#include <wchar.h>
/*
* Display width of UTF-8 character
*/
int utf8_width( unicode_t c) {
#if CYGWIN
assert( sizeof( wchar_t) == 2) ; /* wcwidth only supports UTF-16 */
return (c < 0x10000) ? wcwidth( (wchar_t) c) : -1 ;
#else
return wcwidth( (wchar_t) c) ;
#endif
}
/*
* utf8_to_unicode()
*
* Convert a UTF-8 sequence to its unicode value, and return the length of
* the sequence in bytes.
*
* NOTE! Invalid UTF-8 will be converted to a one-byte sequence, so you can
* either use it as-is (ie as Latin1) or you can check for invalid UTF-8
* by checking for a length of 1 and a result > 127.
*
* NOTE 2! This does *not* verify things like minimality. So overlong forms
* are happily accepted and decoded, as are the various "invalid values".
*/
unsigned utf8_to_unicode( const char *line, unsigned index, unsigned len,
unicode_t *res) {
unicode_t value ;
unsigned c ;
unsigned bytes, mask, i;
if( index >= len)
return 0 ;
*res = c = line[ index] & 0xFFU ;
/*
* 0xxxxxxx is valid one byte utf8
* 10xxxxxx is invalid UTF-8 start byte, we assume it is Latin1
* 1100000x is start of overlong encoding sequence
* Sequence longer than 4 bytes are invalid
* Last valid code is 0x10FFFF, encoding start with 0xF4
*/
if( c <= 0xC1 || c > 0xF4)
return 1;
/* Ok, it's 11xxxxxx, do a stupid decode */
mask = 0x20;
bytes = 2;
while( (c & mask) != 0) {
bytes++;
mask >>= 1;
}
/* bytes is in range [2..4] as c was in range [C2..F4] */
len -= index;
if (bytes > len)
return 1;
value = c & (mask-1);
/* Ok, do the bytes */
line += index;
for (i = 1; i < bytes; i++) {
c = line[i] & 0xFFU ;
if ((c & 0xc0) != 0x80)
return 1;
value = (value << 6) | (c & 0x3f);
}
if( value > 0x10FFFF) /* Avoid 110000 - 13FFFF */
return 1 ;
*res = value;
return bytes;
}
/*
* unicode_to_utf8()
*
* Convert a unicode value to its canonical utf-8 sequence.
*
* NOTE! This does not check for - or care about - the "invalid" unicode
* values. Also, converting a utf-8 sequence to unicode and back does
* *not* guarantee the same sequence, since this generates the shortest
* possible sequence, while utf8_to_unicode() accepts both Latin1 and
* overlong utf-8 sequences.
*/
unsigned unicode_to_utf8( unicode_t c, char *utf8) {
unsigned bytes = 1 ;
assert( c <= 0x10FFFF) ;
#ifdef NDEBUG
if( c > 0x10FFFF) /* Let's assume this is due to sign extension */
c &= 0xFF ;
#endif
if( c <= 0x7f)
*utf8 = (char) c ;
else {
unsigned prefix = 0x40 ;
char *p = utf8 ;
do {
*p++ = (char) (0x80 + (c & 0x3f)) ;
bytes++ ;
prefix >>= 1 ;
c >>= 6 ;
} while( c >= prefix) ;
*p-- = *utf8 ;
*utf8++ = (char) (c - 2 * prefix) ;
if( utf8 < p) { /* swap middle two bytes if 4 bytes utf-8 code */
char c = *p ;
*p = *utf8 ;
*utf8 = c ;
}
}
return bytes ;
}
unsigned utf8_revdelta( unsigned char *p, unsigned pos) {
unsigned delta = 0 ;
if( (*p & 0xC0) == 0x80) {
unsigned char c ;
c = *--p ;
if( (c & 0xE0) == 0xC0) /* valid 2 bytes unicode seq */
delta = 1 ;
else if( ((c & 0xC0) == 0x80) && (pos > 1)) {
c = *--p ;
if( (c & 0xF0) == 0xE0) /* valid 3 bytes unicode seq */
delta = 2 ;
else if( ((c & 0xC0) == 0x80) && (pos > 2))
if( (p[ -1] & 0xF8) == 0xF0) /* valid 4 bytes unicode seq */
delta = 3 ;
}
}
return delta ;
}
/* end of utf8.c */