Re: Ada 95 Numerics questions for the experts

[bobduff@world.std.com (Robert A Duff)]

In article <jeffrey.m.creem-2708970802350001@ljd155.sanders.lockheed.com>,
Jeff Creem <jeffrey.m.creem@lmco.com> wrote:
>...The AdaMajic
>front end is even more limited than not allowing your cool example.
>Even something like
>
>type My_Type is range 0 .. 7;
>for My_Type'size use 3;
>type My_Array is array(1 .. 8) of M
>for My_Array'size use 24;
>
>Is not allowed because the element size of My_Arary is less than 8 it
>rounds to 8 for each element.

Any compiler that supports the above is broken (assuming a typical
32-bit machine).  I doubt if either GNAT or AdaMagic support it (can you
show the exact code you compiled on both compilers?).  A Size clause
does not control the internal layout of components.  Instead, you should use
"for My_Array'Component_Size use 3;" or "for My_Array'Component_Size use 4;"
or "pragma Pack(My_Array);".  Assuming a typical 32-bit machine, the
compiler must support 4-bit components (if it claims to support the SP
annex), and it *might* support 3-bit components -- this applies to both
Pack and Component_Size.  Component_Size is for when you care about the
exact size, whereas Pack is for when you want the compiler to minimize
space, but don't particularly care about (in this case) 3 vs. 4.

For a record with 8 3-bit components, on the other hand, the compiler
must support 3-bit packing.  Perhaps we should have required the same
for arrays that fit in a word.

Note that "for My_Type'size use 3;" is redundant -- My_Type'Size = 3 by
default.  You can put in the Size clause just to get a warm comfy
feeling that the compiler agrees with you on the size, if you like, but
it's not strictly necessary.

- Bob