fftw bench assessment

Started by Unknown July 31, 2009
For starters apologies in advance if I'm in in the wrong NG.

Downloaded fftw and I'm trying to get an assessment on the output
surround the command 'bench -sib246'.

On my machine this outputs:

C:\dev\vc++_2008\fft\fftw>lib /def:libfftw3-3.def
'lib' is not recognized as an internal or external command,
operable program or batch file.

C:\dev\vc++_2008\fft\fftw>bench -s
option -s requires an argument

C:\dev\vc++_2008\fft\fftw>bench -sib256
Problem: ib256, setup: 46.36 ms, time: 2.64 us, ``mflops'': 3881

Three questions:

a) I'm not following what the 46.36ms of 'setup' entails and the di
b) How is time measured here.  Is this as simple as:

  //start the clock
  start = std::clock();
  // stop the clock
  elapsed = (diff_type)std::clock() - start;
  elapsed /= CLOCKS_PER_SEC;

c) bench executed "in-place backward complex transform of size 256".
This in my view means an array length 256 of complex type.  I suspect
the content is irrelevant?  Just trying to get a feel for the 'what
the complex type entails'