Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262356AbTEAE54 (ORCPT ); Thu, 1 May 2003 00:57:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262363AbTEAE54 (ORCPT ); Thu, 1 May 2003 00:57:56 -0400 Received: from [211.167.76.68] ([211.167.76.68]:60306 "HELO soulinfo") by vger.kernel.org with SMTP id S262356AbTEAE5w (ORCPT ); Thu, 1 May 2003 00:57:52 -0400 Date: Thu, 1 May 2003 13:03:18 +0800 From: hugang To: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] Faster generic_fls Message-Id: <20030501130318.459a4776.hugang@soulinfo.com> In-Reply-To: <20030430135512.6519eb53.akpm@digeo.com> References: <200304300446.24330.dphillips@sistina.com> <20030430135512.6519eb53.akpm@digeo.com> X-Mailer: Sylpheed version 0.8.10claws13 (GTK+ 1.2.10; i386-debian-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit =?ISO-8859-1?Q?=CA=D5=BC=FE=C8=CB=A3=BA:?= Andrew Morton =?ISO-8859-1?Q?=CA=D5=BC=FE=C8=CB=A3=BA:?= linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4806 Lines: 200 On Wed, 30 Apr 2003 13:55:12 -0700 Andrew Morton wrote: > Daniel Phillips wrote: > > > > +static inline unsigned fls8(unsigned n) > > +{ > > + return n & 0xf0? > > + n & 0xc0? (n >> 7) + 7: (n >> 5) + 5: > > + n & 0x0c? (n >> 3) + 3: n - ((n + 1) >> 2); > > +} > > return fls_table[n]; > > > That'll be faster in benchmarks, possibly slower in real world. As usual. > Here is table version of the fls. Yes it fast than other. typedef struct fls_table_t { unsigned min; unsigned max; unsigned value; } fls_table_t; static fls_table_t fls_table[] = { {0, 1, 1}, {1, 2, 2}, {2, 4, 3}, {4, 8, 4}, {8, 16, 5}, {16, 32, 6}, {32, 64, 7}, {64, 128, 8}, {128, 256, 9}, {256, 512, 10}, {512, 1024, 11}, {1024, 2048, 12}, {2048, 4096, 13}, {4096, 8192, 14}, {8192, 16384, 15}, {16384, 32768, 16}, {32768, 65536, 17}, {65536, 131072, 18}, {131072, 262144, 19}, {262144, 524288, 20}, {524288, 1048576, 21}, {1048576, 2097152, 22}, {2097152, 4194304, 23}, {4194304, 8388608, 24}, {8388608, 16777216, 25}, {16777216, 33554432, 26}, {33554432, 67108864, 27}, {67108864, 134217728, 28}, {134217728, 268435456, 29}, {268435456, 536870912, 30}, {536870912, 1073741824, 31}, {1073741824, 2147483648, 32}, {0, -1, 32}, }; static inline int fls_table_fls(unsigned n) { unsigned i = 0; do { i++; } while (n <= fls_table[i].max && n > fls_table[i].min); return fls_table[i].value; } --test log is here---- model name : Intel(R) Pentium(R) 4 Mobile CPU 1.60GHz Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.4/specs gcc version 2.95.4 20011002 (Debian prerelease) ==== -march=i686 -O3 ==== test_fls.c:110: warning: decimal constant is so large that it is unsigned 4294967295 iterations of nil... checksum = 4294967295 real 0m22.311s user 0m21.850s sys 0m0.010s 4294967295 iterations of old... checksum = 4294967265 real 0m34.673s user 0m33.960s sys 0m0.000s 4294967295 iterations of new... checksum = 4294967265 real 0m57.702s user 0m56.530s sys 0m0.040s 4294967295 iterations of new2... checksum = 4294967265 real 0m41.709s user 0m40.810s sys 0m0.000s 4294967295 iterations of table... checksum = 4294967295 real 0m22.274s user 0m21.640s sys 0m0.010s ------------------ ==== -march=i686 -O2 ==== test_fls.c:110: warning: decimal constant is so large that it is unsigned 4294967295 iterations of nil... checksum = 4294967295 real 0m29.501s user 0m28.880s sys 0m0.040s 4294967295 iterations of old... checksum = 4294967265 real 0m49.054s user 0m47.840s sys 0m0.040s 4294967295 iterations of new... checksum = 4294967265 real 0m52.331s user 0m51.270s sys 0m0.010s 4294967295 iterations of new2... checksum = 4294967265 real 1m7.043s user 1m5.660s sys 0m0.010s 4294967295 iterations of table... checksum = 4294967295 real 0m45.783s user 0m44.860s sys 0m0.010s ------------------ ==== -O2 ==== test_fls.c:110: warning: decimal constant is so large that it is unsigned 4294967295 iterations of nil... checksum = 4294967295 real 0m34.395s user 0m33.670s sys 0m0.000s 4294967295 iterations of old... checksum = 4294967265 real 0m52.277s user 0m51.230s sys 0m0.000s 4294967295 iterations of new... checksum = 4294967265 real 0m54.750s user 0m53.640s sys 0m0.010s 4294967295 iterations of new2... checksum = 4294967265 real 0m57.728s user 0m56.590s sys 0m0.000s 4294967295 iterations of table... checksum = 4294967295 real 0m44.540s user 0m43.600s sys 0m0.020s ------------------ ==== -O3 ==== test_fls.c:110: warning: decimal constant is so large that it is unsigned 4294967295 iterations of nil... checksum = 4294967295 real 0m16.196s user 0m15.880s sys 0m0.000s 4294967295 iterations of old... checksum = 4294967265 real 0m34.342s user 0m33.630s sys 0m0.010s 4294967295 iterations of new... checksum = 4294967265 real 0m58.554s user 0m57.380s sys 0m0.000s 4294967295 iterations of new2... checksum = 4294967265 real 0m37.140s user 0m36.320s sys 0m0.040s 4294967295 iterations of table... checksum = 4294967295 real 0m21.723s user 0m21.270s sys 0m0.000s ------------------ -- Hu Gang / Steve Email : huagng@soulinfo.com, steve@soulinfo.com GPG FinePrint: 4099 3F1D AE01 1817 68F7 D499 A6C2 C418 86C8 610E ICQ# : 205800361 Registered Linux User : 204016 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/