From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/10809 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] use lookup table for malloc bin index instead of float conversion Date: Sat, 17 Dec 2016 00:50:58 -0500 Message-ID: <20161217055058.GG1555@brightrain.aerifal.cx> References: <20161127141541.GZ5749@port70.net> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1481953878 29138 195.159.176.226 (17 Dec 2016 05:51:18 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 17 Dec 2016 05:51:18 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-10822-gllmg-musl=m.gmane.org@lists.openwall.com Sat Dec 17 06:51:14 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1cI7tl-00065b-6k for gllmg-musl@m.gmane.org; Sat, 17 Dec 2016 06:51:09 +0100 Original-Received: (qmail 13507 invoked by uid 550); 17 Dec 2016 05:51:12 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 13489 invoked from network); 17 Dec 2016 05:51:11 -0000 Content-Disposition: inline In-Reply-To: <20161127141541.GZ5749@port70.net> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:10809 Archived-At: On Sun, Nov 27, 2016 at 03:15:41PM +0100, Szabolcs Nagy wrote: > float conversion is slow and big on soft-float targets. > > The lookup table increases code size a bit on most hard float targets > (and adds 64byte rodata), performance can be a bit slower because of > position independent data access and cpu internal state dependence > (cache, extra branches), but the overall effect should be minimal > (common, small size allocations should be unaffected). > --- > src/malloc/malloc.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c > index b90636c..ce2e97d 100644 > --- a/src/malloc/malloc.c > +++ b/src/malloc/malloc.c > @@ -111,19 +111,29 @@ static int first_set(uint64_t x) > #endif > } > > +static const unsigned char bin_tab[64] = { > + 0, 0, 0, 0,32,33,34,35,36,36,37,37,38,38,39,39, > + 40,40,40,40,41,41,41,41,42,42,42,42,43,43,43,43, > + 44,44,44,44,44,44,44,44,45,45,45,45,45,45,45,45, > + 46,46,46,46,46,46,46,46,47,47,47,47,47,47,47,47, > +}; > + > static int bin_index(size_t x) > { > x = x / SIZE_ALIGN - 1; > if (x <= 32) return x; > + if (x < 512) return bin_tab[x/8]; > if (x > 0x1c00) return 63; > - return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496; > + return bin_tab[x/128] + 16; > } > > static int bin_index_up(size_t x) > { > x = x / SIZE_ALIGN - 1; > if (x <= 32) return x; > - return ((union { float v; uint32_t r; }){(int)x}.r+0x1fffff>>21) - 496; > + x--; > + if (x < 512) return bin_tab[x/8] + 1; > + return bin_tab[x/128] + 17; > } > > #if 0 > -- > 2.10.2 Looks good mostly, but wouldn't it be better to drop the 4 unused entries from the table and add -4's to the indices? Rich