implement hardware CRC32 on ARM

[Former user]

Looks like 64-bit ARM can do hardware CRC32 and maybe hardware CRC32C: https://main.lv/writeup/arm64_assembly_crc32.md K.O.

[Stefan Ritt]

I implemented this now for Apple M1 Arm processor. The code might also work on the Raspberry Pi, but I haven’t tried it. Might need an extra -march flag during compilation. Once tested, this issue can be closed.

[Ben Smith]

As Stefan predicted, the default build on my Pi 4B did not include CRC32 hardware support (so you get a compile-time warning that it isn’t available, but everything still compiles and runs okay).

If I force CRC support with cmake -D CMAKE_CXX_FLAGS="-march=armv8-a+crc" .. then hardware support is included, and the following examples report the same hashes for HW and SW versions.

$ echo "hello" | bin/crc32c_sum
353dd8be
$ echo "hello" | bin/crc32c_sum sw
353dd8be
$ cat src/midas.cxx | bin/crc32c_sum
a637074b
$ cat src/midas.cxx | bin/crc32c_sum sw
a637074b

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