C function to convert hex to binary

A simple C function to convert hex to binary

#include <ctype.h>

inline int cval(char c) {
        if (c>='a') return c-'a'+0x0a;
        if (c>='A') return c-'A'+0x0a;
        return c-'0';
}

/* return value: number of bytes in out, <=0 if error */
int hex2bin(char *str, unsigned char *out){
        int i;
        for(i = 0; str[i] && str[i+1]; i+=2){
                if (!isxdigit(str[i])&& !isxdigit(str[i+1]))
                                return -1;
                out[i/2] = (cval(str[i])<<4) + cval(str[i+1]);
        }
        return i/2;
}