Bit-wise shifting

[imanuelg]

Hello,

I am trying to understand bit-wise shiting.

If I have 54 << 3 I know that 54 is represented in binary as 110110

How do I carry on to get to the final answer ?

Thanks for your help,

Imanuel.

[nielsen]

Hi Imanuel,
The example that you show shift the bit pattern three places to the left inserting zeroes on the new positions, so 54 << 3, will become 110110000 binary which equals decimal 432.

In general, each bit-shift to the left multiplies by 2, so here 54 is multiplied by 2*2*2=2^3, and, generally,
n << m = n*2^m
But beware of the number of available bits (normally 32).

Shifting to the right removes bits from the right, so 54 >> 3 would become 110 binary which is decimal 6. - Each bit-shift to the right divides by 2 and rounds (towards 0) to the closest integer.

Best regards,
Nielsen

[jonnin]

Also, some compilers do funny things with the sign bit. Visual studio shifts everything as a unsigned (all the bits shift) but I have seen compilers shift an integer and leave the sign bit alone, for example

10001 << 1
10010 (some compilers)
00010 (visual)

[Danny]

I recently wrote an article about bitwise operators. It will shed some light on this topic:

http://www.devx.com/getHelpOn/10MinuteSolution/18019