Question

In the code below concatenation is the bottleneck.
As you can see i’ve tried some sophisticated methods to speed this up, but its bloody slow anyway. I would like to know if there is anything i can do to make it faste.

BTW both plain and secret are data read from binary file and they are quite big (around 1mb)

x = b''
if len(plain) < len(secret*8):
    return False
i = 0

for secByte in secret:
    for j in range(8):
        z = setBit(plain[i],0,getBit(secByte,j))
        #x += bytes([z])
        x = x.join([b"", bytes([z])])
        #x = array.array("B",(int(z) for z in x.join([b"", bytes([z])]))).tostring()
        i = i+1

Answer 1

I don’t think you should be using string concatenation at all for this. It would be better to create a mutable bytearray of the full size of the final data and then set each byte. This is very much O(N) and for what you are doing using a bytearray is much more natural than string manipulation:

x = bytearray(len(secret)*8)   # creates an array of zero bytes
i = 0
for secByte in secret:
    for j in range(8):
        x[i] = setBit(plain[i], 0, getBit(secByte, j))
        i += 1