Date: Mon, 23 May 2016 18:59:07 -0400 From: Kurt Lidl <lidl@pix.net> To: Alan Somers <asomers@freebsd.org> Cc: John Baldwin <jhb@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r299090 - in head: etc/mtree include lib/libbluetooth sbin/hastd share/man/man3 sys/dev/xen/blkback sys/kern sys/net sys/sys tests/sys tests/sys/sys usr.sbin/bluetooth/hccontrol Message-ID: <c70d1345-5073-0a53-c074-57f232dbdcc5@pix.net> In-Reply-To: <CAOtMX2iKmX9yOg5P5931E2JSRgS2QO4wRDuE8SmcvmR4JxO_Fw@mail.gmail.com> References: <201605042234.u44MYBMX054443@repo.freebsd.org> <2368543.Vvp613SNcD@ralph.baldwin.cx> <684f4a82-f48c-b2bb-6a72-5c1dfea11a39@pix.net> <CAOtMX2iKmX9yOg5P5931E2JSRgS2QO4wRDuE8SmcvmR4JxO_Fw@mail.gmail.com>
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On 5/23/16 4:30 PM, Alan Somers wrote: > On Fri, May 6, 2016 at 8:45 AM, Kurt Lidl <lidl@pix.net > <mailto:lidl@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? Not to me - as I mentioned, the company went out of business, so catering to its needs is a NOP. Go for it! -Kurt
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