Warning about hardware accelerated CRC32C

[Stefan Ritt]

On my new MacBook Pro M1 (Apple Silicon), midas compiles very well (actually 6x faster!), but I get the annoying error

#warning Hardware accelerated CRC32C is not available.

Now I understand that the M1 does not support hardware accelerated CRC32C, but do I have to see this waring hundreds of times a day? May I propose not to remove the warning, but disable it for the M1? We can test for M1 with the “__arm__” flag, but that seems to me a bit too general, like

#ifdef HAVE_HWCRC32C
  ...
#else

   #ifdef __arm__
      // do nothing
   #else
      #warning Hardware accelerated CRC32C is not available.
   #endif
#endif  

Since the world is going towards Apple Silicon, we should find a good solution for that, since we will soon have many complaints about that (once people realise how good the M1 and M2 are).

Now dumping all preprocesor defines with

gcc -E -dM < /dev/null)

I see these define:

#define __ARM_FEATURE_CRC32 1

so I believe the M1 does have HW acceleration.

Any idea how I can use it?

[Stefan Ritt]

On

https://developer.arm.com/documentation/101028/0012/8--Data-processing-intrinsics

it’s described that we have a

uint32_t __crc32cb (uint32_t a, uint8_t b);

to perform a CRC32 checksum on bytes. Is that the one to use?

[dd1]

this is dupe of bug 330. K.O.

[Stefan Ritt]

So will you have a look or do you want me to implement some arm code?

[dd1]

I will not have time to work on midas until late next week. Luckily midas-2022-a and midas-2022-b seem to be trouble-free so far.

[dd1]

if you want to try it implementing it yourself, note the difference between “CRC32” and “CRC32C” (the “C” version is newer and better). Also note the crc test program in progs/crc32c_sum.cxx. It computes CRC32C checksum of stdin. Ultimately, it should compute the same result on 32-bit x86, 64-bit x86, 32-bit ARM and 64-bit ARM. K.O.

[Stefan Ritt]

Implemented HW CRC32 for Arm procesor