[BHND] create custom CTZ & popcount functions for cross-compilation

[mizhka]

Summary

There are platforms without support of CTZ & popcount. To compile BHND for MIPS, new custom functions are implemented.

Performance of functions seems to nice, but additional tests are welcome!

[landon_landonf.org]

Minor issues aside, LGTM.

@adrian Should we lift out the portable ctz32 for general use? If so, do you have any suggestions on where? cdefs.h? The __bitcount*() macros that already exist don't really belong in types.h:

/*
 * The following are all things that really shouldn't exist in this header,
 * since its purpose is to provide typedefs, not miscellaneous doodads.
 */

sys/dev/bhnd/bhndb/bhndb_private.h

225

I'd like to see this default to __builtin_ctz when available, similar to LZ4_FORCE_SW_BITCOUNT in sys/cddl/contrib/opensolaris/uts/common/fs/zfs/lz4.c

sys/dev/bhnd/bhndb/bhndb_subr.c

402

There's a set of __bitcount* macros in sys/types.h that use __builtin_popcount when available, and fall back to inline portable definitions.

[mizhka]

@landon_landonf.org, corrected.

[adrian]

Hm, is this stuff being called often enough to justify this custom popcount/bitcount stuff?

[mizhka]

Hi @adrian

This stuff is called rare, but builtin_ctz, builtin_popcount are undefined in case of cross-compilation under MIPS.

[adrian]

ok. how do I reproduce these being undefined during cross compile? I'd like to fix that bit first. :)

[mizhka]

Hm.. just try to compile bhnd under MIPS.

Possible way:
I'm using freebsd-wifi-build scripts (thank you for freebsd-wifi-build!!!) : https://github.com/Cka3o4Huk/freebsd-wifi-build/blob/asusrtn16/build/cfg/asusrtn16
../freebsd-wifi-build/build/bin/build asusrtn16 buildkernel
FreeBSD commit with fix: https://github.com/Cka3o4Huk/freebsd/commit/0bcce4188936eeb2696cd51734ce9eef1b5cd928

You can try to checkout both and revert particular patch. But to be honest, I'm not sure that this commit is compilable :(