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Vector shift with Neon error

John Mudumbe over 11 years ago

Note: This was originally posted on 28th March 2013 at http://forums.arm.com

Hi Everyone,

I am trying to shift elements in the vectors with a constant int variable,
but i get an error during compile time saying : arm_neon.h:3850 error: argument must be a constant.
whenever i replace the constant int variable with a constant value , the compiler works just fine.
I have tried to search for solutions online but i am not getting anywhere.

I am using a 2009q arm tool chain and I also tried the using the Dstream tool chain but it is not working for arm cortex A8.
if anyone heres my cry for help and has a solution please reach out and help urgently..

Peter Harris over 11 years ago

Note: This was originally posted on 28th March 2013 at http://forums.arm.com

Can you please give a code sample - it's hard to work out exactly what you have done without seeing the code.
I suspect you are trying to give it a "const int", which is not a compile time constant and therefore invalid. The shift amount is not passed in a register, it is part of the instruction encoding.

HTH,
Iso
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John Mudumbe over 11 years ago
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Simon Pilgrim over 11 years ago
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John Mudumbe over 11 years ago

Note: This was originally posted on 4th April 2013 at http://forums.arm.com

I wanted to know, am running the MVC code on arm-cortex A8 and I want to see how much of the code is optimized, is gprof- good enough or is there any other tool I can use?
I have noticed that the gprof is not consistent in terms of time calculations spend on all procedures.
What other tool can I use to find time precision?
Converting the above code in assmbly language will it also improve the neon optimization or there is no difference at all?
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