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