I have a System.Collections.BitArray array (~3000 items) and I would like to shift all the bits to the left by 1. However the collection doesn't seem to support that operation (i.e. bitArray << 1 not working and there is no method). Any idea on how to do that?
Thanks!
This simple snippet shows a manual way to do it. The value of bitArray[0] is overwritten:
//... bitArray is the BitArray instance
for (int i = 1; i < bitArray.Count; i++)
{
bitArray[i - 1] = bitArray[i];
}
bitArray[bitArray.Count - 1] = false // or true, whatever you want to shift in
Making this an extension method shouldn't be a big deal.
BitArray to a bool[] and than copy the data to another bool[] using offsets. Finally you could recreate your BitArray from the resulting bool[]. But I doubt it will be faster than accessing each element for your ~3000 bits.System.Numerics.BigInteger does indeed support bit shifting.
I am not sure how about efficiency but this extension method does the job
public static BitArray ShiftRight(this BitArray instance)
{
return new BitArray(new bool[] { false }.Concat(instance.Cast<bool>().Take(instance.Length - 1)).ToArray());
}
Recreate bitarray yourself as a wrapper around ulong[]; implementing bitshifts by a number smaller than 64 is a piece of cake that way and it will take less time and kill fewer polar bears than the other suggested approaches. By wary of the "bits that would fall of the end", if you want to keep them you may have to grow the array (or not, if they are zero and you say that non-existing element implicitly hold zero).
Since Core 2.0 (7 years later after this question was asked) there is a built-in method .LeftShift() for this
The easiest way I'd go for off the top of my head is to convert the BitArray to a BigInt or similar structure that supports bitwise shifting and back. Now, the built-int BigInteger in .Net 4 doesn't support shifting I think, but there are others that do, like Mono's implementation.
