Is there a way to detect overflow for example for:

	int i = 2_000_000_000;
	
	int a = i*i*i;
	
	writeln(a);

-> 1073741824

On Wednesday, 4 November 2015 at 03:55:13 UTC, Namal wrote:
> Is there a way to detect overflow for example for:
>
> 	int i = 2_000_000_000;
> 	
> 	int a = i*i*i;
> 	
> 	writeln(a);
>
> -> 1073741824

You can use core.checkedint [1]

---

http://dlang.org/phobos/core_checkedint.html

On Wednesday, 4 November 2015 at 04:22:03 UTC, BBasile wrote:
> On Wednesday, 4 November 2015 at 03:55:13 UTC, Namal wrote:
>> Is there a way to detect overflow for example for:
>>
>> 	int i = 2_000_000_000;
>> 	
>> 	int a = i*i*i;
>> 	
>> 	writeln(a);
>>
>> -> 1073741824
>
> You can use core.checkedint [1]
>
> ---
>
> http://dlang.org/phobos/core_checkedint.html

Is it just an error in the documentation that the return value is stated as sum for the multiplication functions?

On 11/03/2015 10:34 PM, Namal wrote:

>> http://dlang.org/phobos/core_checkedint.html
>
> Is it just an error in the documentation that the return value is stated
> as sum for the multiplication functions?

Yeah, looks like classic copy-paste errors. :)

Ali

On Wednesday, 4 November 2015 at 07:19:09 UTC, Ali Çehreli wrote:
> On 11/03/2015 10:34 PM, Namal wrote:
>
>>> http://dlang.org/phobos/core_checkedint.html
>>
>> Is it just an error in the documentation that the return value is stated
>> as sum for the multiplication functions?
>
> Yeah, looks like classic copy-paste errors. :)
>
> Ali

I take the token for this ddoc fix:

https://github.com/D-Programming-Language/druntime/pull/1429

On Wednesday, 4 November 2015 at 04:22:03 UTC, BBasile wrote:
> On Wednesday, 4 November 2015 at 03:55:13 UTC, Namal wrote:
>> Is there a way to detect overflow for example for:
>>
>> 	int i = 2_000_000_000;
>> 	
>> 	int a = i*i*i;
>> 	
>> 	writeln(a);
>>
>> -> 1073741824
>
> You can use core.checkedint [1]
>
> ---
>
> http://dlang.org/phobos/core_checkedint.html

It says:


"The overflow is sticky, meaning a sequence of operations can be done and overflow need only be checked at the end."

But how can I make multiple operations? I can only put 2 values in the function.

On 11/03/2015 11:52 PM, Namal wrote:

>> http://dlang.org/phobos/core_checkedint.html
>
> It says:
>
>
> "The overflow is sticky, meaning a sequence of operations can be done
> and overflow need only be checked at the end."
>
> But how can I make multiple operations? I can only put 2 values in the
> function.

import core.checkedint;

void main() {
    bool overflowed;
    auto result = adds(int.max, 1, overflowed); // this overflows
    adds(1, 2, overflowed);     // this does not reset the flag

    assert(overflowed);
}

Ali

On Wednesday, 4 November 2015 at 07:59:44 UTC, Ali Çehreli wrote:
> On 11/03/2015 11:52 PM, Namal wrote:
>
>>> http://dlang.org/phobos/core_checkedint.html
>>
>> It says:
>>
>>
>> "The overflow is sticky, meaning a sequence of operations can be done
>> and overflow need only be checked at the end."
>>
>> But how can I make multiple operations? I can only put 2 values in the
>> function.
>
> import core.checkedint;
>
> void main() {
>     bool overflowed;
>     auto result = adds(int.max, 1, overflowed); // this overflows
>     adds(1, 2, overflowed);     // this does not reset the flag
>
>     assert(overflowed);
> }
>
> Ali

wow, this I don't understand at all, how do those two operations connected to each other? By the bool value?

On 11/04/2015 12:11 AM, Namal wrote:

>> import core.checkedint;
>>
>> void main() {
>>     bool overflowed;
>>     auto result = adds(int.max, 1, overflowed); // this overflows
>>     adds(1, 2, overflowed);     // this does not reset the flag
>>
>>     assert(overflowed);
>> }
>>
>> Ali
>
> wow, this I don't understand at all, how do those two operations
> connected to each other? By the bool value?

The 'overflow' parameter is a 'ref' parameter, meaning that these functions modify the actual 'overflowed' variable above. You can imagine that they do not set it to 'false' ever:

Imagine that adds() is implemented like the following:

pure nothrow @nogc @safe
int adds(int x, int y, ref bool overflow) {
    // ...
    if (over_flow_detected) {
        overflow = true;
    }
}

So, the caller's variable can only go from 'false' to 'true', never the other way around. (All of this is just a guess. :) )

Ali

On 11/03/2015 11:34 PM, BBasile wrote:
> On Wednesday, 4 November 2015 at 07:19:09 UTC, Ali Çehreli wrote:
>> On 11/03/2015 10:34 PM, Namal wrote:
>>
>>>> http://dlang.org/phobos/core_checkedint.html
>>>
>>> Is it just an error in the documentation that the return value is stated
>>> as sum for the multiplication functions?
>>
>> Yeah, looks like classic copy-paste errors. :)
>>
>> Ali
>
> I take the token for this ddoc fix:
>
> https://github.com/D-Programming-Language/druntime/pull/1429

Thanks. I've noticed that the parameter of the subtraction functions should be named 'underflow', no?

Ali