static inline int memcmp_P(const void *a1, const void *b1, size_t len) {
    const uint8_t* a = (const uint8_t*)(a1);
    uint8_t* b = (uint8_t*)(b1);
    for (size_t i=0; i<len; i++) {
        uint8_t d = pgm_read_byte(a) - pgm_read_byte(b);
        if (d) return d;
        a++;
        b++;
    }
    return 0;
}
static inline int memcmp_P(const void *a1, const void *b1, size_t len) {
    const uint8_t* a = (const uint8_t*)(a1);
    uint8_t* b = (uint8_t*)(b1);
    for (size_t i=0; i<len; i++) {
        uint8_t d = pgm_read_byte(a) - pgm_read_byte(b);
        if (d) return d;
        a++;
        b++;
    }
    return 0;
}