Thread: Bit shifting - cache simulator

I'm attempting to make a cache simulator in C++. But I need to access individual bits in an integer to figure out where in my "cache" the writing actually gets done. I'm pretty new to bit shifting. Say I'm trying to access the the bits of the int 5, which are its "address". I'm simulating a direct mapped cache. I need to find its tag, the set it goes into, and which line. How do I use bit shifting to access the bits to aquire the tag, the index bits, offset bits, block number...all these pieces in order to actually find where I store it in the cache. Thank you!

I need to break the bits up into 3 sections: tag, set index, and block index. I think I can figure out the set and block index sizes based on the values passed in. The tag bits are just the remaining ones. And I'm hard coding values such as cache size (C) - 1024, number of physical address bits (m) - 32, block size (B) - 2, number of lines per set (E) - 1 (again, directly mapped cache). How would this look?

Originally Posted by rcgldr

If the data is in a single integer, you just need to do a right shift followed by an and operation. If it's two 32 bit integers, and you need to shift right "n" bits, you shift the "upper" word left (32 - n) bits then "and" off the unwanted bits, shift the lower word right "n" bits, "and" off unwanted bits, then "or" the result together. You could also use a structure with bit fields and let the compiler do the work for you. If this is a 2 way or more associative cache, you'll also need to implement a hashing algorithm to emulate the associative (content addressable) memory.

For now I'm just attempting a directly mapped cache

I'm actually passing ints to a function which takes in unsigned longs so I can handle up to 64 bits