[Gm2] GCC / GM2 Optimizer

[Michael Riedl]

Hallo Gaius,

another curious result.

MODULE TestMachEps;

FROM STextIO IMPORT WriteLn;
FROM SLongIO IMPORT WriteFloat;

PROCEDURE MachEps() : LONGREAL;

          VAR eps,EinsPlusEps : LONGREAL;
BEGIN
      eps:=0.5; EinsPlusEps:=1.5;
      WHILE (EinsPlusEps # 1.0) DO
        eps:=0.5*eps;
        EinsPlusEps:=1.0+eps;
      END;
      RETURN 2.0*eps;
END MachEps;

VAR   eps : LONGREAL;

BEGIN
     eps := MachEps();

     WriteLn; WriteLn;
     WriteString(" MachEps = "); WriteFloat(eps,20,10);
     WriteLn; WriteLn;
END TestMachEps.

Compile attached with -O0 and with -O2. In the latter the machine 
precision equals to zero ...
By the way - same behavior with REAL.

Gruß

Michael

PS : GFortran does not show this result - see attached Fortran 90. Maybe 
that will give an idea as both are using the same backend.

TestMachEps.f90
Description: Text Data