(j3.2006) TKR for C Interop
Wed Feb 28 18:58:44 EST 2007
Aleksandar Donev wrote:
>On Wednesday 28 February 2007 13:01, Bill Long wrote:
>>Struct components either have documented names or not. This is direction
>OK, I was not aware of "small-group" decisions to change the API to a mixed
>struct/function approach (which is fine by me, modulo some details I complain
>For such an approach, the Fortran->C descriptor function should set the rank
>and type information to invalid values if they are not available (say 0 for
>rank and -1 for size of the element in bytes), or set them to valid values if
>they are available in the Fortran descriptor.
Yes. The current thinking is give these standardized invalid values
names to provide some implementation flexibility and make the user code
a little more self documenting. The values would be otherwise
impossible values, such as negative values for sizes of things.
>>The other functions create/destroy a shell C descriptor
>Why is this necessary? If we expect that the C descriptor will not match most
>vendors descriptors (and Craig can easily tell you this for several
>compilers), what is the point of making the C struct soo opaque? Let's allow
>the programmer to directly declare C descriptors without "creating" and
>"destroying" them. Some components of the C struct can still be opaque.
>In C, structs are either of fixed size (this means rank-independent in our
>particular case), or they have flexible array members. I don't know of an
>in-between alternative. Which one of these two is this C struct you are
>BTW, C also has "incomplete types" which have unspecified size:
The incomplete type option has come up as a candidate. The simplest is
fixed size. In the worst case I can think of, this could be ~140 64-bit
words, though for vendors that support higher than rank 15 it could be
even more. Do you think this would be acceptable? If so, I'm happy to
get rid of two more functions. And it would allow the descriptors to go
onto the stack which gives better performance and reduces the chance for
>"The use of a type specifier of the syntactic classes
><structure-type-reference> ... without a preceding definition...is alowed
>when the size of the structure is not required, including when declaring:
>1. pointers to the structure
>2. a typedef name as a synonym for the structure"
>This is like a "handle" to a descriptor.
>I see more open (and more fundamental) questions than just the triplets.
>J3 mailing list
>J3 at j3.scs.gmu.edu
Bill Long longb at cray.com
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Bioinformatics Software Development fax: 651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120
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