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Date: Fri, 16 Nov 2012 08:48:32 +0100
From: magnum <>
Subject: Re: scalar mode

On 16 Nov, 2012, at 7:00 , Marc Brinkmann <> wrote:
> Based on our discussion here
> may i kindly ask you to repeat the instrctions for scalar mode?
> I just joind the Mailinglist some weeks ago, and i cannot even find via
> google, what you are refereing to.
> I only find that post from john-dev but honestly, i don't know what do i
> need to perform to enable scalar mode

The post you mention does show the two code blocks involved, but I meant this:

But I can re-write it a little longer here: The Office 2007/2010 OpenCL formats will currently run in scalar mode on nvidias and on AMD GCN (Tahiti), because scalar mode faster on those. On everything else (ie. CPU or older AMD's) they will currently use vectorizing. Due to register pressure, Office2013 will currently only run vectorized on CPU, not on any GPU. When vectorized mode is used, the format name is printed with "[OpenCL 4x]" as opposed to just "[OpenCL]".

To force scalar mode, you need to edit the host source (eg. src/opencl_office2010_fmt.c), search for "VF = 4" and comment out (or #if 0...#endif) that whole conditional block, so VF is never changed from its initial value of 1. Then you need to edit the corresponding OpenCL kernel (eg. src/opencl/ and modify the very first #ifdef so that we always #define SCALAR. Then re-build and retry. Please report the outcome.

Or, just wait until tomorrow and I'll post a patch that adds two options to GPU builds of JtR: --request-scalar and --request-vectorized. This will let you do it without hacking the code. With some luck this will also let me find any bug in my code (forcing vectorized on the Tahiti just to trigger the bug) but I strongly suspect we are dealing with driver bugs here as usual.


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