Wrong code gen / missing warning / my mistake?

[Ali Çehreli]

On 09/10/2012 10:08 AM, Benjamin Thaut wrote:
 > The following code
 >
 >
 > bool endsWith(string str, string end)
 > {
 > size_t to = str.length - end.length;

size_t is an unsigned type. That expression above is very dangerous.

 > for(sizediff_t i = str.length - 1; i >= to; --i)

Yes, sizediff_t is signed, but...

 > {
 > if(str[i] != end[i-to])

to is unsigned so 'i-to' is unsigned.

 > return false;
 > }
 > return true;
 > }
 >
 > int main(string[] args)
 > {
 > return cast(int)endsWith("blub", "blub");
 > }
 >
 > compiled with dmd 2.060 gives me a range violation. (with i = -1)
 > although it shouldn't. If I change to from size_t "to" sizediff_t
 > everything is fine. The comparison between the unsigned "to" and the
 > signed "i" is not done correctly.
 >
 > Is this a code gen bug? Or is it missing a compiler warning / error? Or
 > is this entierly my fault?
 >
 > Kind Regards
 > Benjamin Thaut

Ali