From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/10811 Path: news.gmane.org!.POSTED!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: [PATCH v2] use lookup table for malloc bin index instead of float conversion Date: Sat, 17 Dec 2016 15:03:24 +0100 Message-ID: <20161217140323.GM16379@port70.net> References: <20161127141541.GZ5749@port70.net> <20161217055058.GG1555@brightrain.aerifal.cx> <20161217073600.GZ18078@example.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 1481983435 11844 195.159.176.226 (17 Dec 2016 14:03:55 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 17 Dec 2016 14:03:55 +0000 (UTC) User-Agent: Mutt/1.6.0 (2016-04-01) To: musl@lists.openwall.com Original-X-From: musl-return-10824-gllmg-musl=m.gmane.org@lists.openwall.com Sat Dec 17 15:03:52 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 1cIFaZ-0002Tj-5h for gllmg-musl@m.gmane.org; Sat, 17 Dec 2016 15:03:51 +0100 Original-Received: (qmail 21672 invoked by uid 550); 17 Dec 2016 14:03:52 -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 21543 invoked from network); 17 Dec 2016 14:03:38 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: <20161217073600.GZ18078@example.net> Xref: news.gmane.org gmane.linux.lib.musl.general:10811 Archived-At: 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 60byte 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). --- * u-uy74@aetey.se [2016-12-17 08:36:00 +0100]: > On Sat, Dec 17, 2016 at 12:50:58AM -0500, Rich Felker wrote: > > 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? > > Wouldn't this enlarge the code more than reduce the data? most targets have a load instruction with small offset and on some targets the compiler emits relocation against (tab-4) instead of tab so the code size is not affected. 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..c38c46f 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[60] = { + 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/8-4]; if (x > 0x1c00) return 63; - return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496; + return bin_tab[x/128-4] + 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/8-4] + 1; + return bin_tab[x/128-4] + 17; } #if 0 -- 2.10.2