[fpc-pascal] Loss of precision when using math.Max()

[Paul Nance]

It's hard to make things fool proof, fool's are too ingenius.


On Jul 2, 2018 6:14 PM, "Wolf" <wv99999 at gmail.com> wrote:

> Not so long ago, Florian was proudly bragging about "Pascal does not allow
> you to shoot yourself in the foot
> <http://www.toodarkpark.org/computers/humor/shoot-self-in-foot.html>"
>
> What about this little program:
>
> program Project1;
>
> var a,b: byte;
> begin
>   a:=1;
>   b:=a*(-1);
>   writeln(b);    // result: 255
> end.
>
>
> The result is obviously correct, given how the variables are declared. But
> there are no compiler warnings / errors that the assignment b:=a*(-1) is
> fishy, to put it mildly. And if you are serious about strong typing, it
> ought to be illegal, with a suitable complaint from the compiler.
>
> Who is shooting whom in the foot?
>
> Wolf
>
> On 02/07/2018 20:22, Santiago A. wrote:
>
> El 01/07/2018 a las 10:27, C Western escribió:
>
> On 29/06/18 21:55, Sven Barth via fpc-pascal wrote:
>
> More confusingly, if a single variable is used, the expected Max(Double,
> Double) is called:
>
> function Max(a, b: Double): Double; overload;
> begin
>   WriteLn('Double');
>   if a > b then Result := a else Result := b;
> end;
>
> function Max(a, b: Single): Single; overload;
> begin
>   WriteLn('Single');
>   if a > b then Result := a else Result := b;
> end;
>
> var
>   v1: Double;
>   v2: Single;
> begin
>   v1 := Pi;
>   v2 := 0;
>   WriteLn(v1);
>   WriteLn(Max(v1,0));
>   WriteLn(Max(v1,0.0));
>   WriteLn(Max(v1,v2));
> end.
>
> Prints:
>  3.1415926535897931E+000
> Single
>  3.141592741E+00
> Double
>  3.1415926535897931E+000
> Double
>  3.1415926535897931E+000
>
> If this is not a bug, it would be very helpful if the compiler could print
> a warning whenever a value is implicitly converted from double to single.
>
> Well, pascal is a hard typed language, but not that hard in numeric
> issues. I think it is a little inconsistent that it implicitly converts
> '0.0' to double but '0 to single.
>
> Nevertheless, I think it is a bug. It doesn't choose the right overloaded
> function
>
> But the main is this:
> you have several overload options for max
> 1 extended, extended
> 2 double, double
> 3 single, single
> 4 int64, int64
> 5 integer, integer
>
> When it finds (double, single), why does  it choose (single, single)
> instead of (double, double)?
> The natural behavior should be to widen to the greater parameter, like it
> does in expressions.
>
>
>
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>
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