Re: [Bug-gnubg] wrong dice colours in html export and below board in GUI

[Petr Kadlec]

At 14:42 28.11.2003 +0100, you wrote:
> In the above subclauses, multiplication and division are in the same
> subclause, so there is no precedence there. This leaves the compiler
> free to evaluate:
>
> 3 * ss * DIE_WIDTH / 2 as any of:
>
> (3 * ss * DIE_WIDTH) / 2
> (3 * ss) * (DIE_WIDTH / 2)
> 3 * (ss * DIE_WIDTH / 2)
>
> or to rearrange things at compile time:
>
> 3 * DIE_WIDTH / 2 evaluated in any order, replaced with the constant
> result which gets multiplied by ss at run time.
>
> Can we please insert parentheses where required to force the desired
> evaluation (a comment as to why the parentheses are there would not go
> amiss). Otherwise the above patch corrects the problem only courtesy
> of the vagaries of the current compiler being used and could change if
> another compiler or a later/earlier version of this compiler is used.

Hmmmm, I believe this is a big misunderstanding (IMHO). The terms of the 
expressions may be evaluated in any order, but that is NOT THE SAME as the 
associativity of the terms. Take e.g. an expression like this:

result = f1() * f2() / f3();

The cited clause of the C standard is saying only that the functions f1(), 
f2(), f3() may be called in any (unspecified) order. BUT, the computation 
of the result takes place from left to right (as * and / are 
left-associative operators), like that:

temp = result_from_f1 * result_from_f2;
result = temp / result_from_f3;

The parentheses do change the associativity, but they DO NOT change the 
order of evaluation, so even they would not solve the mentioned problem, ...
The only things that changes the order of evaluation are: special operators 
that have their order of evaluation set (i.e. those mentioned -- function 
call, &&, ||, ?:, comma), or split the evaluation to multiple statements.

With regards,
Petr Kadlec

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We must believe in free will. We have no choice. - Isaac Bashevis Singer
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Petr Kadlec, student
Faculty of Electrical Engineering
The Czech Technical University
address@hidden, ICQ #68196926