Is there an easy way to find two values that, when multiplied together, create an accurate bitmap?

Question

Is there an easy way to find two values that, when multiplied together, create an accurate bitmap?

For testing purposes, I need to find two 64-bit integer values that are exactly multiplied by a 128-bit intermediate value with a specific bit pattern. Obviously I can generate the intermediate value I want and divide by random values until I find a combination that works, but is there a more efficient way?

+2

c ++ testing multiplication

Sean mcallister Sep 16 '09 at 15:53

source to share

3 answers

I was going to post the same as j_random_hacker. I'll just add that if a 128 bit number is prime or has a base ratio greater than 64 bits then there will be no solution to your problem.

+4

Jeremy bourque Sep 16 09 at 16:03

source to share

And I'll just add to the previous comment: if a 128-bit number has a base ratio greater than 64 bits, then it certainly has a ratio less than 64 bits :)

+1

Eugene N. Sep 16 09 at 17:31

source to share

j_random_hacker · Accepted Answer · 2009-09-16T15:59:16+0000

This problem sounds like a whole factorization . Unfortunately, no fast algorithms are known, but after looking at this Wikipedia page it seems that there are some (possibly complex) algorithms that are faster than trial division.

Is there an easy way to find two values ​​that, when multiplied together, create an accurate bitmap?

More articles:

Is there an easy way to find two values that, when multiplied together, create an accurate bitmap?