source: trunk/sys/dietlibc/mbrtowc.c @ 50

#include "dietlocale.h"
#include <wchar.h>
#include <errno.h>

static mbstate_t internal;

size_t mbrtowc(wchar_t *pwc, const char *s, size_t n, mbstate_t *ps) {
  size_t i;
  if (!ps) ps=&internal;
  if (!s) {
    if (ps->count) {
      errno=EILSEQ;
      return (size_t)-1;
    } else {
      ps->count=0;
      ps->sofar=0;
      return 0;
    }
  }
  for (i=0; i<n; ++i) {
    unsigned char c=s[i];
    switch (lc_ctype) {
    case CT_8BIT:
      if (pwc) { *pwc=c; ++pwc; }
      return (!!c);
    case CT_UTF8:
      if (ps->count) {
        /* we have an unfinished multibyte sequence */
        if ((c&0xc0)!=0x80) {
          /* expected a continuation, didn't get one */
kaputt:
          errno=EILSEQ;
          ps->count=0;
          return (size_t)-1;
        }
        ps->sofar=(ps->sofar << 6) + (c & 0x3f);
        if (!--ps->count) {
complete:
          if (pwc) { *pwc=ps->sofar; ++pwc; }
          if (ps->sofar) {
            ps->sofar=0;
            return i+1;
          } else {
            ps->count=0; ps->sofar=0;
            return 0;
          }
        }
      } else {
        if (c&0x80) {   /* start of multibyte sequence? */
          unsigned char x=c<<1;
          unsigned char cnt=0;
          while (x&0x80) {
            x<<=1;
            ++cnt;
          }
          if (!cnt || cnt>5) goto kaputt;
          ps->sofar=x>>(cnt+1);
          ps->count=cnt;
        } else {
          ps->sofar=c;
          goto complete;
        }
      }
    }
  }
  return n;
}