Page Comparison

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When we look at this way, we see that in a a 2 byte integer, we could for example store a an RGBA color value (Red, Green, Blue, Alpha). This could be really helpful, if we say wanted to send color values from a computer to an Arduino in the form of integers. This could in some cases be much faster than sending 4 values independently. In the next section we will see how it’s done.

Bit Shifting Operators

The three bit shifting operators are as follows:

• << the left shift operator

• >> the (signed) right shift operator.

Note, we are using unsigned numbers here to keep things simple, refer to the Arduino reference page if you need to work with signed numbers.

Shift right:

unsigned int a = 32356;  // binary: 0111111001100100
unsigned int b = a>>8    // binary: 0000000001111110

Shift left:

unsigned int a = 32356;  // binary: 0111111001100100
unsigned int b = a<<8    // binary: 0110010000000000

In both the above cases, some of the bits have been shift into oblivion, and 0s have filled the new spaces

Putting it to use

So we can move bits around, but how do we extract sets of values out of one variable? One solution is to bracket the values we need into smaller variables with a specific length.

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Here we have the our color values stored as binary in one variable:

11111111000000001111111100000000

11111111 00000000 11111111 00000000

red | green | blue | alpha

Each block is 8 bits, or one byte. So we will use the byte variable chop off and keep the last 8 bits:

        unsigned int RGBAvalue = #FF00FF16 // binary: 11111111000000001111111100010101
        byte ALPHA = RGBAvalue; // binary: 00010101

We can repeat this process, in combination with the shift right operator to extract all the values:

        unsigned int RGBAvalue = #FF00FF00 // we might get this value from serial or BLE
        byte RED =  RGBAvalue >> 24;
        byte GREEN = RGBAvalue >> 16;
        byte BLUE = RGBAvalue >> 8;
        byte ALPHA = RGBAvalue; 

P5js / javascript code

But how do will combine the values to start with, before we seperate them on the Arduino? Here we are assuming that you want to do that on your computer, in a P5js web application that might use serial or BLE, or wifi to communicate with Arduino.

        unsigned int RGBAvalue = #FF00FF00 // we might get this value from serial or BLE
        byte RED =  RGBAvalue >> 24;
        byte GREEN = RGBAvalue >> 16;
        byte BLUE = RGBAvalue >> 8;
        byte ALPHA = RGBAvalue;