bit-shift doesn't produce expected 0!

[fizzleBomb]

After running this:

unsigned long long x = (unsigned long long)-1;
int y = 64;
x = x >> y;

the value of x is 0xffffffffffffffff though I'd have expected 0. Strangely,
shifting by 63 produces 1 as expected. Any idea what's up with that?

I'm using gcc 4.0.2 if that's relevant.

 

[Kai-Uwe Bux]

After running this:

unsigned long long x = (unsigned long long)-1;
int y = 64;
x = x >> y;

the value of x is 0xffffffffffffffff though I'd have expected 0.
Strangely, shifting by 63 produces 1 as expected. Any idea what's up with
that?

Undefined behavior [5.8/1]:

The shift operators << and >> group left-to-right.
[...]
The operands shall be of integral or enumeration type and integral
promotions are performed. The type of the result is that of the promoted
left operand. The behavior is undefined if the right operand is negative,
or greater than or equal to the length in bits of the promoted left
operand.

I'm using gcc 4.0.2 if that's relevant.

It isn't.


Best

Kai-Uwe Bux

 

[fizzleBomb]

Undefined behavior [5.8/1]:

The shift operators << and >> group left-to-right.
[...]
The operands shall be of integral or enumeration type and integral
promotions are performed. The type of the result is that of the promoted
left operand. The behavior is undefined if the right operand is
negative, or greater than or equal to the length in bits of the promoted
left operand.

I'm using gcc 4.0.2 if that's relevant.

It isn't.


Best

Kai-Uwe Bux

Thanks much!