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#include <wchar.h>
size_t mbsnrtowcs(wchar_t *restrict wcs, const char **restrict src, size_t n, size_t wn, mbstate_t *restrict st)
{
size_t l, cnt=0, n2;
wchar_t *ws, wbuf[256];
const char *s = *src;
if (!wcs) ws = wbuf, wn = sizeof wbuf / sizeof *wbuf;
else ws = wcs;
/* making sure output buffer size is at most n/4 will ensure
* that mbsrtowcs never reads more than n input bytes. thus
* we can use mbsrtowcs as long as it's practical.. */
while ( s && wn && ( (n2=n/4)>=wn || n2>32 ) ) {
if (n2>=wn) n2=wn;
n -= n2;
l = mbsrtowcs(ws, &s, n2, st);
if (!(l+1)) {
cnt = l;
wn = 0;
break;
}
if (ws != wbuf) {
ws += l;
wn -= l;
}
cnt += l;
}
if (s) while (wn && n) {
l = mbrtowc(ws, s, n, st);
if (l+2<=2) {
if (!(l+1)) {
cnt = l;
break;
}
if (!l) {
s = 0;
break;
}
/* have to roll back partial character */
*(unsigned *)st = 0;
break;
}
s += l; n -= l;
/* safe - this loop runs fewer than sizeof(wbuf)/8 times */
ws++; wn--;
cnt++;
}
if (wcs) *src = s;
return cnt;
}
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