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       mbrtowc.c - scc - simple c99 compiler
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       ---
       mbrtowc.c (748B)
       ---
            1 #include <wchar.h>
            2 
            3 #include "../libc.h"
            4 
            5 #undef mbrtowc
            6 
            7 size_t
            8 mbrtowc(wchar_t *restrict pwc, const char *restrict s, size_t n,
            9         mbstate_t *restrict ps)
           10 {
           11         unsigned char *t = (unsigned char *) s;
           12         unsigned long wc;
           13         unsigned c;
           14         int i, len, maxlen;
           15 
           16         if (s == NULL)
           17                 return 0;
           18 
           19         wc = c = *t++;
           20         for (len = 0; n > 0 && c & 0x80; --n, ++len)
           21                 c <<= 1;
           22         if (n == 0 || len == 1 || len == 8)
           23                 return -1;
           24         if (len == 0)
           25                 goto return_code;
           26 
           27         wc = (c & 0xFF) >> len;
           28         for (i = 0; i < len-1; i++) {
           29                 if (((c = *t++) & 0xC0) != 0x80)
           30                         return -1;
           31                 wc <<= 6;
           32                 wc |= c & 0x3F;
           33         }
           34 
           35         if (!_validutf8(wc, &maxlen) || len != maxlen)
           36                 return -1;
           37 
           38 return_code:
           39         if (pwc)
           40                 *pwc = wc;
           41         if (*s == '\0')
           42                 return 0;
           43         return t - (unsigned char *) s;
           44 }