From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/10751 Path: news.gmane.org!.POSTED!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: [PATCH] use lookup table for malloc bin index instead of float conversion Date: Sun, 27 Nov 2016 15:15:41 +0100 Message-ID: <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 1480256157 28186 195.159.176.226 (27 Nov 2016 14:15:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 27 Nov 2016 14:15:57 +0000 (UTC) User-Agent: Mutt/1.6.0 (2016-04-01) To: musl@lists.openwall.com Original-X-From: musl-return-10764-gllmg-musl=m.gmane.org@lists.openwall.com Sun Nov 27 15:15:53 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 1cB0FF-0006aU-8y for gllmg-musl@m.gmane.org; Sun, 27 Nov 2016 15:15:53 +0100 Original-Received: (qmail 3969 invoked by uid 550); 27 Nov 2016 14:15:55 -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 3922 invoked from network); 27 Nov 2016 14:15:53 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline Xref: news.gmane.org gmane.linux.lib.musl.general:10751 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 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