Bitwise OR on strings for large strings in c#

Question

I have two strings(with 1's and 0's) of equal lengths(<=500) and would like to apply Logical OR on these strings.

How should i approach on this. I'm working with c#.

When i consider the obvious solution, reading each char and applying OR | on them, I have to deal with apx, 250000 strings each with 500 length. this would kill my performance.

Performance is my main concern.

Thanks in advance!

Answer 1

This is fastest way:

string x="";
string y="";
StringBuilder sb = new StringBuilder(x.Length);
for (int i = 0; i < x.Length;i++ )
{
    sb.Append(x[i] == '1' || y[i] == '1' ? '1' : '0');
}
string result = sb.ToString();

Answer 2

Since it was mentioned that speed is a big factor, it would be best to use bit-wise operations.

Take a look at an ASCII table:

• The character '0' is 0x30, or 00110000 in binary.
• The character '1' is 0x31, or 00110001 in binary.

Only the last bit of the character is different. As such - we can safely say that performing a bitwise OR on the characters themselves will produce the correct character.

Another important thing we can do is do to optimize speed is to use a StringBuilder, initialized to the initial capacity of our string. Or even better: we can reuse our StringBuilder for multiple operations, although we have to ensure the StringBuilder has enough capacity.

With those optimizations considered, we can make this method:

string BinaryStringBitwiseOR(string a, string b, StringBuilder stringBuilder = null)
{
    if (a.Length != b.Length)
    {
        throw new ArgumentException("The length of given string parameters didn't match");
    }

    if (stringBuilder == null)
    {
        stringBuilder = new StringBuilder(a.Length);
    }
    else
    {
        stringBuilder.Clear().EnsureCapacity(a.Length);
    }

    for (int i = 0; i < a.Length; i++)
    {
        stringBuilder.Append((char)(a[i] | b[i]));
    }
    return stringBuilder.ToString();
}

Note that this will work for all bit-wise operations you would like to perform on your strings, you only have to modify the | operator.