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Re: RFC: Naming convention for ILP64 variant of BLAS/LAPACK




On Mon, 22 Oct 2018 at 18:17:32 +0100, Ben Hutchings wrote:
> On Mon, 2018-10-22 at 15:07 +0000, Mo Zhou wrote:
> > Here are some references:
> > 
> > 1. https://software.intel.com/en-us/mkl-linux-developer-guide-using-the-ilp64-interface-vs-lp64-interface
> > 
> >    The Intel MKL ILP64 libraries use the 64-bit integer type (necessary
> >    for indexing large arrays, with more than 231-1 elements), whereas
> >    the LP64 libraries index arrays with the 32-bit integer type.
> [...]
> 
> The correct C types for indexing arrays are ptrdiff_t and size_t. 
> These are already 64-bit in LP64 ABIs.  So this seems like a workaround
> for code using the wrong types.

Do BLAS/LAPACK really mean ILP64, or do they really mean "ABI with large
array indexes"?

A true ILP64 ABI would be one where open() takes a 64-bit flags parameter
and returns a 64-bit result. As Ben says, that's a question of operating
system ABI, not an individual library's ABI.

If BLAS/LAPACK want a version that uses 64-bit quantities in places where
they previously used ints, they should change the type used, not the
meaning of "int".

Prior art 1: in the CPython 2.5 ABI, PyList_GetItem took an int argument,
but in CPython 2.6+ it takes a Py_ssize_t argument, where Py_ssize_t
is a signed integer the same size as a size_t - that's a ssize_t on
platforms that support that type, like Debian. This required an ABI
break for Python extensions, but not for the whole operating system.

Prior art 2: libpcre has multiple ABI versions that use different sizes
for an abstract character in a Unicode string (libpcre3 for 8-bit units
encoding Unicode in UTF-8, libpcre16-3 for 16-bit units encoding Unicode
in UTF-16, and libpcre32-3 for 32-bit units encoding Unicode in UCS-4)
but nobody claims that the different libpcre ABIs have different sizes
for 'char'.

    smcv