[Oberon] REAL math

[Jörg Straube]

Zdenek

In addition to my experiments on WinAos, I now played with LinuxAos or to be precise with DarwinAos on the Mac. Here my program:
- - - - - - - - - - - 
MODULE Untitled;
IMPORT Commands;

PROCEDURE Do*(ctx: Commands.Context);
  VAR
    epsilon, r: REAL;
    digits: INTEGER;
  BEGIN
    epsilon := 1; digits :=0;
    WHILE 1+epsilon # 1 DO epsilon := epsilon /10; INC(digits) END;
    ctx.out.Int(digits, 0); ctx.out.Ln;
 
    r := 480/100*100;
    ctx.out.Float(r, 20); ctx.out.Ln;
    ctx.out.Float(r-480, 20); ctx.out.Ln;
    
    epsilon := 1; digits :=0;
    WHILE 1.D0+epsilon # 1 DO epsilon := epsilon /10; INC(digits) END;
    ctx.out.Int(digits, 0); ctx.out.Ln;
       
    r := SHORT(480.D0/100*100);
    ctx.out.Float(r, 20); ctx.out.Ln;
    ctx.out.Float(r-480, 20); ctx.out.Ln;
        
  END Do;

BEGIN
END Untitled.Do
- - - - - - - - - - - 

The output is
8
  4.80000030518E+002
  3.05175781250E-005
16
  4.80000000000E+002
  0.00000000000E+000

As the result of the WHILE shows, in this AOS environment expressions are evaluated with 8 digits of accuracy (REAL).
Hence the compiler by default evaluates internally constant expressions like „480/100*100“ with REALs as well.
If I force the compiler to use LONGREAL (by writing 1.D0 and 480.D0) the results are more accurate.

br
Jörg

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