Bug#743642: Suggestion: Enable 64-bit Index Support on AMD64

[Barak A. Pearlmutter]

Package: libarmadillo-dev
Version: 1:4.100.2+dfsg-2
Severity: wishlist

When compiling the mlpack machine learning library, which links to
Armadillo, the configuration scripts spits out this bon mot:

  -- Found Armadillo: /usr/lib/libarmadillo.so (found suitable version "4.100.2", required is "3.6.0") 
  CMake Warning at CMakeLists.txt:81 (message):
    This is a 64-bit system, but Armadillo was compiled without 64-bit index
    support.  Consider recompiling Armadillo with ARMA_64BIT_WORD to enable
    64-bit indices (large matrix support).  MLPACK will still work without
    ARMA_64BIT_WORD defined, but will not scale to matrices with more than 4
    billion elements.

which sounds reasonable.

At least, it sounds reasonable when you're doing machine learning with
big datasets.  (I suppose there are other circumstances where 32-bit
indexes make more sense.  But that argument would likely apply to all
pointers.  Which would constitute a new 32-bit-user-pointers
amd64-instructions "architecture".  Which is in fact under active
development.  But it does seem hard to pretty hard to argue against
64-bit index support on arch amd64.)

					--Barak.
--
Barak A. Pearlmutter
 Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland
 http://www.bcl.hamilton.ie/~barak/