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bitshiftLeft.adoc

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<<
bitshift left
Structure
Bitwise Operators

<< Bitshift Left

Description

The left shift operator << causes the bits of the left operand to be shifted left by the number of positions specified by the right operand.

Syntax

variable << number_of_bits;

Parameters

variable: Allowed data types: byte, int, long.
number_of_bits: a number that is < = 32. Allowed data types: int.

Example Code

int a = 5;      // binary: 0000000000000101
int b = a << 3; // binary: 0000000000101000, or 40 in decimal

Notes and Warnings

When you shift a value x by y bits (x << y), the leftmost y bits in x are lost, literally shifted out of existence:

int x = 5;  // binary: 0000000000000101
int y = 14;
int result = x << y;  // binary: 0100000000000000 - the first 1 in 101 was discarded

Attention: Left-shifting a constant (like e.g. "1") means left-shifting a two-byte integer! If you want to shift it more than 14 steps to the left (e. g. for the use with a set of 4 daisy-chained shift registers), you will have to cast it, otherwise you won’t get reasonable resluts:

uint32_t x1 = 1 << 14;  // binary: 100000000000000
uint32_t x2 = 1 << 15;  // binary: 11111111111111111000000000000000
uint32_t y1 = uint32_t(1) << 14;  // binary: 100000000000000
uint32_t y2 = uint32_t(1) << 15;  // binary: 1000000000000000

If you are certain that none of the ones in a value are being shifted into oblivion, a simple way to think of the left-shift operator is that it multiplies the left operand by 2 raised to the right operand power. For example, to generate powers of 2, the following expressions can be employed:

   Operation  Result
   ---------  ------
    1 <<  0      1
    1 <<  1      2
    1 <<  2      4
    1 <<  3      8
    ...
    1 <<  8    256
    1 <<  9    512
    1 << 10   1024
    ...

The following example can be used to print out the value of a received byte to the serial monitor, using the left shift operator to move along the byte from bottom(LSB) to top (MSB), and print out its Binary value:

// Prints out Binary value (1 or 0) of byte
void printOut1(int c) {
  for (int bits = 7; bits > -1; bits--) {
    // Compare bits 7-0 in byte
    if (c & (1 << bits)) {
      Serial.print("1");
    }
    else {
      Serial.print("0");
    }
  }
}

See also