val % size >= size?!

[KarlisRepsons]

I have this short question: under what obscure circumstances can this happen?

[kbw]

What type is val and size?

[jdd]

Unless I'm mistaken, this will be true when size is negative and val > size (e.g. val = -1 and size = -2). I don't know if this makes sense within the context of your program, but it certainly is possible for the expression to be true.

[KarlisRepsons]

And how about this:

unsigned int size_ = 123;
const unsigned int hash( char* key ) const
{
    unsigned int val = 0;
    while ( *key )
    {
        val = val<<1 ^ *key;
        key++;
    }
    if ( val < 0 )
        return (-val) % size_;
    return val % size_;
}

Is the statement impossible there? Also, please tell me, if its completely safe to assume, that bit shifting wont make negative result! (should be, but I am not sure...)

[Bazzy]

As you are working with unsigned types you can't get negative values and val would never be less than zero so line 11 would never be executed

[KarlisRepsons]

Interesting, I should delete or compiler is able to optimise code and avoid testing? It can be, that leaving those couple of lines is useful...

[jsmith]

val is unsigned. unsigneds can never be negative. Lines 10 and 11 can safely be removed as never executing. (If you compiled with warnings turned on you'd get a "warning: comparison of unsigned vs. signed" warning and possibly also a "comparison is always false due to limited range of data type" on line 10).

EDIT: well, so actually, g++ gives no warnings at all, even with -Wall... but still, the code can never execute.