Problems with shift left operator (dmd 0.169)

[Lionello Lunesu]

KlausO wrote:
> Hello D-experts,
> 
> I created a little test program which IMHO shows
> not the expected behaviour.
> Is this a bug or not ?
> 
> module testshift;
> 
> import std.stdio;
> 
> void main()
> {
>   uint val_a = (1 << 32);
> 
>   uint shift = 32;
>   uint val_b = (1 << shift);
> 
>   writefln("Result: ", val_a, "  ", val_b);
>   assert(val_a == val_b);
> }
> 
> Output is as follows:
> Result: 0  1
> Error: AssertError Failure testshift(14)


The problem here is: what values would you expect?

1<<32 is too big for an uint, so the 0 from the constant folding is 
correct, BUT the "shl" instructions (the one << translates into) only 
looks at the lower 5 bits, which are 0 (32 & 0x1F == 0), so also the 1 
is correct.

I don't think we'd want extra overhead for something like <<, so I 
suppose we let "<<" behave like the instruction "shl". Which means 
there's only one solution: let the compiler complain.

Come to think of it, it should already have complained: 1<<32 does not 
fit into an uint! But DMD gives no error, not even a warning (-w)...

L.