brightness_bitshifter8()

uint8_t brightness_bitshifter8 ( uint8_t * brightness_src, uint8_t * brightness_dst, uint8_t max_shifts )

inline

Definition at line 14 of file brightness_bitshifter.h.

                                                                                                            {
    uint8_t src = *brightness_src;
    if (*brightness_dst == 0 || src == 0) {
        return 0;
    }
    // Steal brightness from brightness_src and give it to brightness_dst.
    // After this function concludes the multiplication of brightness_dst and brightness_src will remain
    // constant.
    // This algorithm is a little difficult to follow and I don't understand why it works that well,
    // however I did work it out manually and has something to do with how numbers respond to bitshifts.
    uint8_t curr = *brightness_dst;
    uint8_t shifts = 0;
    for (uint8_t i = 0; i < max_shifts && src > 1; i++) {
        if (curr & 0b10000000) {
            // next shift will overflow
            break;
        }
        curr <<= 1;
        src >>= 1;
        shifts++;
    }
    // write out the output values.
    *brightness_dst = curr;
    *brightness_src = src;
    return shifts;
}

Referenced by fl::five_bit_bitshift().

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