source: asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/multibyte/mbrtowc.c@ 337

#include <stdlib.h>
#include <wchar.h>
#include <errno.h>
#include "internal.h"

size_t mbrtowc(wchar_t *restrict wc, const char *restrict src, size_t n, mbstate_t *restrict st)
{
        static unsigned internal_state;
        unsigned c;
        const unsigned char *s = (const void *)src;
        const unsigned N = n;
        wchar_t dummy;

        if (!st) st = (void *)&internal_state;
        c = *(unsigned *)st;
        
        if (!s) {
                if (c) goto ilseq;
                return 0;
        } else if (!wc) wc = &dummy;

        if (!n) return -2;
        if (!c) {
                if (*s < 0x80) return !!(*wc = *s);
                if (MB_CUR_MAX==1) return (*wc = CODEUNIT(*s)), 1;
                if (*s-SA > SB-SA) goto ilseq;
                c = bittab[*s++-SA]; n--;
        }

        if (n) {
                if (OOB(c,*s)) goto ilseq;
loop:
                c = c<<6 | *s++-0x80; n--;
                if (!(c&(1U<<31))) {
                        *(unsigned *)st = 0;
                        *wc = c;
                        return N-n;
                }
                if (n) {
                        if (*s-0x80u >= 0x40) goto ilseq;
                        goto loop;
                }
        }

        *(unsigned *)st = c;
        return -2;
ilseq:
        *(unsigned *)st = 0;
        errno = EILSEQ;
        return -1;
}