Thread: Putting several hashes together. Better than md5/sha1?

Hi everyone. If I am to example putting several hash function together, would it be as safe as to make an md5 or a sha1 hash? I wonder because I have a program and it generate a md5 hash too slowly. It can only generate up to 20000 hashes (on a laptop) in a second and it is not enough. My idea to fix this is too use several fast hash functions as murmurhash2 and superfasthash, like this:

Code:

unsigned int* hashes = new unsigned int[2];
hashes[0] = MurmurHash2(str,len);
hashes[1] = SuperFastHash(str,len);

But is this good in that sense it decrease collision chance than a md5 hash? if I am using a third hash function, would it decrease collision even more? If not, do anyone have any tips on how I can generate a hash fast which have extremely low collision chance?

Thanks in advance!

To hash 8192 bytes and check if (using a multimap) that sequence of bytes have been added before.

no, only when I am adding data. I do it now, but it is so annoying that the "adding part" of my program is limited to how fast it can make md5 hashes Well, the program will run on a much better machine later so, maybe should I wait to see how good it is performing there before I do some changes ;P

But, Thanks for your answers

Hi again. I got a new idea, instead of make 2 hashes of same data, what about:

Code:

hashes[0] = MurmurHash2(str,d);
hashes[1] = MurmurHash2(str,d/2);

?

This would not generate same hash so easy, or?