#include "internal.h"

int
utf8·bytetorune(rune* r, byte* s)
{
    int c[UTFmax], i;
    rune l;

    c[0] = *(ubyte*)(s);
    if(c[0] < Tx) {
        *r = c[0];
        return 1;
    }

    l = c[0];
    for(i = 1; i < UTFmax; i++) {
        c[i]  = *(ubyte*)(s+i);
        c[i] ^= Tx;
        if (c[i] & Testx) goto bad;

        l = (l << Bitx) | c[i];
        if(c[0] < Tbyte(i + 2)) {
            l &= RuneX(i + 1);
            if (i == 1) {
                if (c[0] < Tbyte(2) || l <= Rune1)
                    goto bad;
            } else if (l <= RuneX(i) || l > RuneMax)
                goto bad;
            if (i == 2 && SurrogateMin <= l && l <= SurrogateMax)
                goto bad;

            *r = l;
            return i + 1;
        }
    }
bad:
    *r = RuneErr;
    return 1;
}