C fromHex 十六進位字串轉位元組

const unsigned char *fromhex(const char *str){    static unsigned char buf[512];    size_t len = strlen(str) / 2;    if (len > 512) len = 512;    for (size_t i = 0; i < len; i++) {        unsigned char c = 0;        if (str[i * 2] >= '0' && str[i*2] <= '9')             c += (str[i * 2] - '0') << 4;        if ((str[i * 2] & ~0x20) >= 'A' && (str[i*2] & ~0x20) <= 'F')             c += (10 + (str[i * 2] & ~0x20) - 'A') << 4;        if (str[i * 2 + 1] >= '0' && str[i * 2 + 1] <= '9')             c += (str[i * 2 + 1] - '0');        if ((str[i * 2 + 1] & ~0x20) >= 'A' && (str[i * 2 + 1] & ~0x20) <= 'F')            c += (10 + (str[i * 2 + 1] & ~0x20) - 'A');        buf[i] = c;    }    return buf;}