Aligned memory and posix_memalign

A worrisome (to me) issue with the volk library is the use of
posix_memalign() in the qa tests. The worry is:

  • posix_memalign() will never work on Windows with Microsoft’s runtime
    library *

That means that code that uses posix_memalign won’t work on Windows with
MinGW or Microsoft native compilers. (The problem is not that memory
alignment is difficult; it is simply that there is no memory-aligned
version
of malloc() in the Microsoft API that works with free().)

At present, posix_memalign is used in GNU Radio in machine-dependent
code
(gcell, altivec, and arm7) and in the volk qa tests. If we can replace
it
in volk and avoid its spread, we can continue to use GNU Radio on
Windows.

One option is to use something like malloc16Align/free16Align (in
malloc16.{h,c}) in gnuradio-core. Can we structure the code to make
this
available in volk, and anywhere else it is needed? We can add a version
to
do more general alignment if needed. Would it help to wrap aligned
buffers
in a C++ class to make it easier to catch errors (such as using free()
on a
malloc16Align() buffer)?

Note that simply enhancing our own missing/posix_memalign function using
_mingw_aligned_malloc() or Microsofts’s _aligned_malloc() won’t work
because
memory allocated with those cannot be released with free().

Trying not to cause too much trouble,

– Don W.

On Sun, Mar 6, 2011 at 9:48 AM, Don W. [email protected]
wrote:

Note that simply enhancing our own missing/posix_memalign function using
_mingw_aligned_malloc() or Microsofts’s _aligned_malloc() won’t work because
memory allocated with those cannot be released with free().

Trying not to cause too much trouble,

– Don W.

Thanks for bringing this up. I’ll look into it and we’ll try to figure
out a
general solution for all platforms involved.

Tom

here is my fix attempt:
http://gnuradio.org/cgit/jblum.git/commit/?h=wip/volk/remove_posix_memalign

-josh

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