Am 17.02.2024 um 02:12 schrieb Ern Aldo via fpc-pascal:
It is possible math is being done differently by the compiler than by
programs? For math-related source code, the compiler compiles the
instructions and writes them to the program file for execution at
runtime. For compile-time constant calculations that produce run-time
constant values, one would expect the compiler to compile the
instructions, execute them during compilation, and write the resulting
value to the program file for use at runtime. Such instructions are
discarded, because the program does not need them. If math is being
compiled differently for program-executed calculations versus
compiler-executed calculations, then that would be a problem.
I'll try to comment on this using some source code which hopefully does
conform to FPC,
but I am not sure, because I am not familiar with FPC standards. Please
look:
Const
A_const = Integer(8427);
B_const = Byte(33);
C_const = Single(1440.5);
y1 := A_const + C_const / B_const;
y2 := 8427 + 1440.5 / 33;
In my understanding, in the first assignment the constants have types,
which are given to them
by the const declarations. And that's why the computation is done using
single precision.
This would be OK for me, because the developers decided to do the
definitions this way,
and so he or she takes responsibility.
If the computation is done at run time or at compile time, DOESN'T MATTER.
In the second case, using literal constants, the compiler should do the
math using the maximum
precision available (IMO), because one constant (1440.5) has a FP
representation. It does and should
not matter, that this constant can be stored exactly in a single FP
field. Here again:
If the computation is done at run time or at compile time, DOESN'T MATTER.
Maybe this is not how FPC works today, but IMO this is how it should be
done, because we want
(IMO) Pascal to be a clear language which is simple to explain, easy to
use and easy to implement.
The case would be different, of course, if you do the same casting in
the y2 case as in the const
declarations.
Kind regards
Bernd
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