There are two bit shift operators in C++:
<<is the left shift operator>>is the right shift operator
These can be very useful especially in SRAM memory, and can often optimize your code. << can be understood as a multiplication of the left operand by 2 raised to the right operand power.
>> is the same but is similar to a division. The ability to manipulate bits is often very useful and can make your code faster in many situations.
Let's multiply a variable using bit shifting.
int a = 4; int b = a << 3;
The second row multiplies the variable a by 2 to the third power, so b now contains 32. On the same lines, division can be carried out as follows:
int a = 12 ; int b = a >> 2;
b contains 3 because >> 2 equals division by 4. The code can be faster using these operators because they are a direct access to binary operations without using any function of the Arduino core like pow() or even the other operators.
Instead of using a big, two-dimensional table to store, for instance, a bitmap shown as follows:
const prog_uint8_t BitMap[5][7] = {
// store in program memory to save RAM
{1,1,0,0,0,1,1},
{0,0,1,0,1,0,0},
{0,0,0,1,0,0,0},
{0,0,1,0,1,0,0},
{1,1,0,0,0,1,1} }; We can use use the following code:
const prog_uint8_t BitMap[5] = {
// store in program memory to save RAM
B1100011,
B0010100,
B0001000,
B0010100,
B1100011 }; In the first case, it takes 7 x 5 = 35 bytes per bitmap. In the second one, it takes only 5 bytes. I guess you've just figured out something huge, haven't you?
The following is a direct consequence of the previous tip. If we want to set up pins 8 to 13 as output, we could do it like this:
void setup() {
int pin;
for (pin=8; pin <= 13; ++pin) {
pinMode (pin, LOW);
}
}But this would be better:
void setup() {
DDRB = B00111111 ; // DDRB are pins from 8 to 15
}In one pass, we've configured the whole package into one variable directly in memory, and no pinMode function, structure, or variable name needs to be compiled.