Re: Ada.Strings.Fixed.Count raises Storage_Error

[Georg Bauhaus <bauhaus@futureapps.invalid>]

On 12.05.16 13:36, Xavier Petit wrote:

> with Ada.Strings.Fixed, Ada.Integer_Text_IO;
> use  Ada.Strings.Fixed, Ada.Integer_Text_IO;
>
> procedure Test_Count is
>     S : constant String (Positive'Last - 2 .. Positive'Last) := "Ada";
> begin
>     Put (Count (Source => S,                         Pattern => "AA"));
>     Put (Count (Source => S (S'First .. S'Last - 1), Pattern => "A"));
>     Put (Count (Source => S,                         Pattern => "A"));
> end;
>
> Output on gnat-gcc 5.3.1 :
>
>            0          1
>
> raised STORAGE_ERROR : stack overflow or erroneous memory access

Compiling such that the RTS is recompiled will result in

raised CONSTRAINT_ERROR : a-strsea.adb:102 overflow check failed

The message points at a line in the implementation of
Ada.Strings.Search.Count, for the third of the calls. It reads

      Ind := Ind + 1;

where Ind looks seems to be go along with the Index of your S,
IINM. Effectively (PL1 = Pattern'Length - 1 being 0), then loop
there boils down to this:

    while Ind <= Source'Last loop
       if Pattern = Source (Ind .. Ind) then
          ...
       else
          Ind := Ind + 1;
       end if;
    end loop;

And this would explains the overflow.

Just the slip-up that Ada subtypes were designed to help prevent?


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