Messages in this thread | | | Date | Fri, 18 Apr 2008 21:13:47 -0700 (PDT) | From | dean gaudet <> | Subject | Re: Alternative implementation of the generic __ffs |
| |
On Fri, 18 Apr 2008, Joe Perches wrote:
> On Fri, 2008-04-18 at 18:11 -0700, dean gaudet wrote: > > have you benchmarked it? > > I modified Alexander's benchmark: > http://lkml.org/lkml/2008/4/18/267 > to include 32 and 64 bit variants called smallest. > > On an old ARM:
i'm guessing the 32-bit constants suck :(
the code could be modified to use 16-bit constants only -- it would add some dependent operations though (to move the hot bit into the low 16-bits).
-dean
> > $ gcc --version gcc (GCC) 3.4.6 > > $ cat /proc/cpuinfo > Processor : Intel StrongARM-110 rev 4 (v4l) > BogoMIPS : 262.14 > Hardware : Rebel-NetWinder > Revision : 57ff > Serial : 000000000000185c > > $ gcc -Os -fomit-frame-pointer ffs.c > $ ./a.out > Original: 3180 tics, 8379 tics > New: 4280 tics, 8890 tics > Smallest: 4027 tics, 7835 tics > Empty loop: 1543 tics, 2260 tics > > $ gcc -O2 -fomit-frame-pointer ffs.c > $ ./a.out > Original: 3161 tics, 7843 tics > New: 4778 tics, 8783 tics > Smallest: 4408 tics, 7149 tics > Empty loop: 1515 tics, 2140 tics > > $ gcc -O3 -fomit-frame-pointer ffs.c > $ ./a.out > Original: 3078 tics, 7692 tics > New: 4714 tics, 8671 tics > Smallest: 4344 tics, 7117 tics > Empty loop: 1444 tics, 2024 tics
| |