#define LOW(exp) ((exp) & 0xFF)
#define HIGH(exp) (((exp) & 0xFF00) >> 8)

uint16_t prng(uint16_t v) {
    uint16_t low = LOW(v);
    uint16_t high = HIGH(v);

    uint16_t mul_low = low * 5;
    //high byte is ignored
    uint8_t mul_high = LOW(high * 5);

    //need to check for overflow, since the final addition is adc as well
    uint16_t v1 = mul_high + HIGH(mul_low) + 1;
    uint8_t carry = HIGH(v1) ? 1 : 0;

    uint16_t v2 = (LOW(v1) << 8) + LOW(mul_low);

    return v2 + 0x11 + carry;
}