On Fri, May 6, 2016 at 8:45 AM, Kurt Lidl <l...@pix.net> wrote:
> On 5/5/16 12:31 PM, John Baldwin wrote: > >> On Wednesday, May 04, 2016 10:34:11 PM Alan Somers wrote: >> >>> Author: asomers >>> Date: Wed May 4 22:34:11 2016 >>> New Revision: 299090 >>> URL: https://svnweb.freebsd.org/changeset/base/299090 >>> >>> Log: >>> Improve performance and functionality of the bitstring(3) api >>> >>> Two new functions are provided, bit_ffs_at() and bit_ffc_at(), which >>> allow >>> for efficient searching of set or cleared bits starting from any bit >>> offset >>> within the bit string. >>> >>> Performance is improved by operating on longs instead of bytes and >>> using >>> ffsl() for searches within a long. ffsl() is a compiler builtin in both >>> clang and gcc for most architectures, converting what was a brute force >>> while loop search into a couple of instructions. >>> >>> All of the bitstring(3) API continues to be contained in the header >>> file. >>> Some of the functions are large enough that perhaps they should be >>> uninlined >>> and moved to a library, but that is beyond the scope of this commit. >>> >> >> Doesn't switching from bytes to longs break the ABI? That is, setting >> bit 9 >> now has a different representation on big-endian systems (0x00 0x01 >> before, >> now 0x00 0x00 0x01 0x00 on 32-bit BE, and 4 more leading 0 bytes on >> 64-bit). >> This means you can't have an object file compiled against the old header >> pass a bitstring to an object file compiled against the new header on >> big-endian >> systems. >> >> Even on little-endian systems if an old object file allocates storage for >> a >> bitstring the new code might read off the end of it and fault (or return >> garbage if bits are set in the extra bytes it reads off the end)? >> >> Is the API is so little used we don't care? >> >> > Just as a note - at my prior job (Pi-Coral, now defunct) we used this > API everywhere in the dataplane code of our product. Since the company > is gone, that particular use-case doesn't matter anymore. > > At the very least, this deserves a mention in the release notes, and > also UPDATING! > > -Kurt > > UPDATING is updated as of r300539. Any objection to merging this to stable/10? _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
