What does a bitwise shift left or right do and what is it used for

Question

I ve seen the operators  gt  gt  and  lt  lt  in various code that I ve looked at  none of which I actually understood   but I m just wondering what they actually do and what some practical uses of them are  If the shifts are like x   2 and x   2  what is the real difference from actually using the   and   operators  Is there a performance difference

User · Answer

Left bit shifting to multiply by any power of two and right bit shifting to divide by any power of two.

For example, x = x * 2; can also be written as x<<1 or x = x*8 can be written as x<<3 (since 2 to the power of 3 is 8). Similarly x = x / 2; is x>>1 and so on.

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Left shift  It is equal to the product of the value which has to be shifted and 2 raised to the power of number of bits to be shifted  Example  1  lt  lt  3 0000 0001  --- gt  1 Shift by 1 bit 0000 0010 ---- gt  2 which is equal to 1 2 1 Shift By 2 bits 0000 0100 ---- gt  4 which is equal to 1 2 2 Shift by 3 bits 0000 1000 ---- gt  8 which is equal to 1 2 3  Right shift  It is equal to quotient of value which has to be shifted by 2 raised to the power of number of bits to be shifted  Example  8  gt  gt  3 0000 1000  --- gt  8 which is equal to 8 2 0 Shift by 1 bit 0000 0100 ---- gt  4 which is equal to 8 2 1 Shift By 2 bits 0000 0010 ---- gt  2 which is equal to 8 2 2 Shift by 3 bits 0000 0001 ---- gt  1 which is equal to 8 2 3

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Left Shift  x   x   2 value  normal operation   x  lt  lt  value   bit-wise operation     x   x   16  which is the same as 2 4   The left shift equivalent would be x   x  lt  lt  4  Right Shift  x   x   2 value  normal arithmetic operation   x  gt  gt  value  bit-wise operation     x   x   8    which is the same as 2 3   The right shift equivalent would be x   x  gt  gt  3

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Some examples   Bit operations for example converting to and from Base64  which is 6 bits instead of 8  doing power of 2 operations  1  lt  lt  4 equal to 2 4 i e  16  Writing more readable code when working with bits  For example  defining constants using 1  lt  lt  4 or 1  lt  lt  5 is more readable

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Left bit shifting to multiply by any power of two and right bit shifting to divide by any power of two.

For example, x = x * 2; can also be written as x<<1 or x = x*8 can be written as x<<3 (since 2 to the power of 3 is 8). Similarly x = x / 2; is x>>1 and so on.

User · Answer

Here is an applet where you can exercise some bit-operations  including shifting  You have a collection of bits  and you move some of them beyond their bounds  1111 1110  lt  lt  2 1111 1000  It is filled from the right with fresh zeros     0001 1111  gt  gt  3 0000 0011  Filled from the left  A special case is the leading 1  It often indicates a negative value - depending on the language and datatype  So often it is wanted  that if you shift right  the first bit stays as it is  1100 1100  gt  gt  1 1110 0110  And it is conserved over multiple shifts  1100 1100  gt  gt  2 1111 0011  If you don t want the first bit to be preserved  you use  in Java  Scala  C    C as far as I know  and maybe more  a triple-sign-operator  1100 1100  gt  gt  gt  1 0110 0110  There isn t any equivalent in the other direction  because it doesn t make any sense - maybe in your very special context  but not in general  Mathematically  a left-shift is a   2  2 left-shifts is a   4 and so on  A right-shift is a    2 and so on

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Yes  I think performance-wise you might find a difference as bitwise left and right shift operations can be performed with a complexity of o 1  with a huge data set  For example  calculating the power of 2   n  int value   1  while  exponent lt n                  Print out current power of 2         value   value  2     Equivalent machine level left shift bit wise operation         exponent                      Similar code with a bitwise left shift operation would be like  value   1  lt  lt  n   Moreover  performing a bit-wise operation is like exacting a replica of user level mathematical operations  which is the final machine level instructions processed by the microcontroller and processor

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Here is an example   include quot stdio h quot   include quot conio h quot   void main         int rm  vivek      clrscr        printf  quot Enter any numbers t E g   1  2  5 quot        scanf  quot  d quot    amp rm      rm   5 0101   lt  lt  2  two step add zero s   so the value is 10100     printf  quot This left shift value d  d quot   rm  rm lt  lt 4       printf  quot This right shift value d  d quot   rm  rm gt  gt 2       getch

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The bit shift operators are more efficient as compared to the   or   operators  In computer architecture  divide    or multiply    take more than one time unit and register to compute result  while  bit shift operator  is just one one register and one time unit computation

[bit-manipulation] What does a bitwise shift (left or right) do and what is it used for?

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