Confused by a line in matth.inc (2.6.2 rtl)

[Pasqualish]

This line is in mathh.inc in /usr/share/fpcsrc/2.6.2/rtl

Code: Pascal  [Select][+][-]

1.     function pi : ValReal;[internproc:fpc_in_pi_real];

I see a function named pi that takes no arguments and returns a ValReal type, but I don't know how to interpret the rest of that declaration.

[Thaddy]

[internproc:fpc_in_pi_real] means that valreal will be resolved by the compiler into pi with as resolution the correct max real type (single, double, extended, etc) for the platform: eg. i386 = extended, x86_64 = double.
It is related to the compilerproc modifiier that is added in the implementation section if it is not a compiler const (here it is a compiler const) See e.g. declaration for Abs and implementation for Abs.
You can only use this construct in the interface section of a unit and only if there is a corresponding  compiler intrinsic or const for that.
Basically never use it yourself unless you are a compiler dev.. It is as magical as magic comes....

Code: Pascal  [Select][+][-]

1. //mathh.inc interface
2. function abs(d : ValReal) : ValReal;[internproc:fpc_in_abs_real];
3. // compproc.inc implementation
4. function fpc_abs_real(d : ValReal) : ValReal;compilerproc;
5.  

In the case of pi, the const is first resolved through a  index for known constants and then a FPU instruction if available and subsequently through the compiler function getpi in ninl.pas translated at compile time  into a const of the correct size.

Code: Pascal  [Select][+][-]

1.  
2.     function getpi : bestreal;
3.       begin
4.       {$ifdef x86}
5.         { x86 has pi in hardware }
6.         result:=pi;
7.       {$else x86}
8.         {$ifdef cpuextended}
9.           result:=MathPiExtended.Value;
10.         {$else cpuextended}
11.           result:=MathPi.Value;
12.         {$endif cpuextended}
13.       {$endif x86}
14.       end;

ValReal itself is determined through a set of defines based on the resolution of the cpu or fpu for the platform.

So basically: nice syntax, but not for you (or me)...

[Pasqualish]

Thanks!