Re: Problem using Ada.Text_IO.Modular_IO

[micronian2@gmail.com]

On Jul 14, 6:12 am, Georg Bauhaus <rm.dash-bauh...@futureapps.de>
wrote:
> anon schrieb:
[snip]
> Q: What routines does the compiler generate for Unsigned_64
>     but not for "mod 2**64" and vice versa?
> A: None.
>

Your "mod 2**64" won't get Shift_Arithmetic_Right, Rotate_Left, and
Rotate_Right. After some thought, I realized that you can simulate
Rotate_Left/Right with shift operations. For example,
Rotate_Left(Value, 3) can be performed by doing:

 Value := (Value * 2**3) or (Value / 2**29) (note: assuming value is
32-bits)

For constant values, the compiled output has a good chance of being
the same for either "mod 2**64" and Unsigned_64. But what about cases
where the shift offsets are not known at compile time?  I wrote two
little test programs to see how user defined shift and rotate
operations for "mod**64" compared to those that were predefined for
Interfaces.Unsigned_64 using GNAT GPL2008. For the shift left/right
operations, the output was the pretty much the same. For the rotate
left/right, the ones for Unsigned_64 generated less code and did not
need as many calls to the run-time system. Of course, this is all just
based on one compiler. I don't know what other compilers do. Actually
I do recall the old GreenHills AdaMULTI 3.0 compiler implemented the
operations as calls to C functions.

Anyhow, I think I said enough on this.