[Ffmpeg-devel] yet another silly int vs. float benchmark

[Michael Niedermayer]

Hi

On Saturday 21 May 2005 19:42, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > Hi
> >
> > heres another benchmark proggy, advantages over the others
> > 1. pure c
> > 2. ~40 lines of code, can be easily done in less i know ...
> > 3. tries to test both the case where each instruction depends upon the
> > previous one and where the instructions are a little more independant
>
> I tried it on my Alpha PCA56, but I keep getting a SIGFPE on the first
> float operation.  I disabled the first float add test, and got these
> numbers:
>
> 100 ; needed     3 cycles ->     3 cycles per operation
> 100 iv[0]+=iv[1];iv[1]+=iv[0]; needed   229 cycles ->   114 cycles per
> operation 100 iv[0]*=iv[1];iv[1]*=iv[0]; needed  1827 cycles ->   913
> cycles per operation 100 fv[0]*=fv[1];fv[1]*=fv[0]; needed   804 cycles -> 
>  402 cycles per operation 100
> iv[0]+=iv[1];iv[1]+=iv[2];iv[2]+=iv[3];iv[3]+=iv[4];iv[4]+=iv[5]; needed  
> 282 cycles ->    56 cycles per operation 100
> iv[0]*=iv[1];iv[1]*=iv[2];iv[2]*=iv[3];iv[3]*=iv[4];iv[4]*=iv[5]; needed 
> 2032 cycles ->   406 cycles per operation 100
> fv[0]+=fv[1];fv[1]+=fv[2];fv[2]+=fv[3];fv[3]+=fv[4];fv[4]+=fv[5]; needed  
> 511 cycles ->   102 cycles per operation 100
> fv[0]*=fv[1];fv[1]*=fv[2];fv[2]*=fv[3];fv[3]*=fv[4];fv[4]*=fv[5]; needed  
> 511 cycles ->   102 cycles per operation
>
> Can someone (Falk?) explain the FPE?  It goes away with -mieee, but

hmm, try to set fv[] to 0 instead of 1, maybe it overflows

[...]
-- 
Michael