[Issue 8011] BigInt ++ and -- do wrong thing on negative numbers

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=8011


Ary Borenszweig <ary at esperanto.org.ar> changed:

           What    |Removed                     |Added
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                 CC|                            |ary at esperanto.org.ar


--- Comment #3 from Ary Borenszweig <ary at esperanto.org.ar> 2012-05-01 23:57:53 PDT ---
(In reply to comment #1)
> The root cause is in bigint.d, in the opUnary() function. BigInt uses an
> underlying BigUint and maps the ++ and -- operators directly through to the
> BigUint as addition and subtraction, respectively, disregarding the BigInt's
> sign. However, this is wrong. Signed ++ and -- must be passed through as
> subtraction and addition, respectively.
> 
> I modified the function by commenting out the two errant lines and replacing
> them each with a correct one. This is a proof-of-concept fix for the bug. 
> 
>     // non-const unary operations
>     BigInt opUnary(string op)() if (op=="++" || op=="--")
>     {
>         static if (op=="++")
>         {
>             //data = BigUint.addOrSubInt(data, 1UL, false, sign);
>             data = BigUint.addOrSubInt(data, 1UL, sign ? true : false, sign);
>             return this;
>         }
>         else static if (op=="--")
>         {
>             //data = BigUint.addOrSubInt(data, 1UL, true, sign);
>             data = BigUint.addOrSubInt(data, 1UL, sign ? false : true, sign);
>             return this;
>         }
>     }

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