src/multibyte/mbtowc.c

   1 /*
   2  * This code was written by Rich Felker in 2010; no copyright is claimed.
   3  * This code is in the public domain. Attribution is appreciated but
   4  * unnecessary.
   5  */
   6
   7 #include <stdlib.h>
   8 #include <wchar.h>
   9 #include <errno.h>
  10 #include "internal.h"
  11
  12 int mbtowc(wchar_t *restrict wc, const char *restrict src, size_t n)
  13 {
  14         unsigned c;
  15         const unsigned char *s = (const void *)src;
  16         wchar_t dummy;
  17
  18         if (!s) return 0;
  19         if (!n) goto ilseq;
  20         if (!wc) wc = &dummy;
  21
  22         if (*s < 0x80) return !!(*wc = *s);
  23         if (MB_CUR_MAX==1) return (*wc = CODEUNIT(*s)), 1;
  24         if (*s-SA > SB-SA) goto ilseq;
  25         c = bittab[*s++-SA];
  26
  27         /* Avoid excessive checks against n: If shifting the state n-1
  28          * times does not clear the high bit, then the value of n is
  29          * insufficient to read a character */
  30         if (n<4 && ((c<<(6*n-6)) & (1U<<31))) goto ilseq;
  31
  32         if (OOB(c,*s)) goto ilseq;
  33         c = c<<6 | *s++-0x80;
  34         if (!(c&(1U<<31))) {
  35                 *wc = c;
  36                 return 2;
  37         }
  38
  39         if (*s-0x80u >= 0x40) goto ilseq;
  40         c = c<<6 | *s++-0x80;
  41         if (!(c&(1U<<31))) {
  42                 *wc = c;
  43                 return 3;
  44         }
  45
  46         if (*s-0x80u >= 0x40) goto ilseq;
  47         *wc = c<<6 | *s++-0x80;
  48         return 4;
  49
  50 ilseq:
  51         errno = EILSEQ;
  52         return -1;
  53 }