在Intel CPU上选择32至64位固有CRC

Question

I need to calculate CRC in order to form a hash function on an INTEL machine and came up with the following two intrinsic functions:

1. _mm_crc32_u32
2. _mm_crc32_u64

In my project, I am dealing with 32-bit variables and my dilemma is between shifting and ORing each two variables (thus creating a 64-bit variable) and then using the 64-bit CRC or run the 32-bit CRC on each of the two 32-bit variables.

I can't find anywhere the amount of cycles that each one of these functions take, and from the Intel function specifications it is unclear which one is preferable.

The same dilemma also applies on the 16-bit version of the CRC function:

_mm_crc32_u16

I tried checking it by taking the time before and after the CRC. The results were pretty much the same. So I need a more sophisticated way of calculating it.

Answer 1

Don't use CRC for hash values. It's not the same kind of thing. Use the murmurhash for classic computer science hashing needs (that is, not huge cryptographic strength hashes). That also has implementations for different widths.

I don't understand what you mean: you have two 32-bit values and want a hash of that? That might be sensible or might not, depending on why. Can you clarify what you are trying to accomplish?