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From:Vladislav Vaintroub Date:December 19 2008 11:53am
Subject:RE: Fix for bug#41582
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> -----Original Message-----
> From: Lars-Erik.Bjork@stripped [mailto:Lars-Erik.Bjork@stripped]
> Sent: Friday, December 19, 2008 11:32 AM
> To: falcon@stripped
> Subject: Fix for bug#41582
> 
> Hi all!
> 
> I have a fix for the decimal/numeric bug 41582.
> 
> As explained in the reference manual [1], decimals are stored using a
> binary format that packs nine decimal digits into four bytes, where
> any leftover digits require some fraction of four bytes.
> 
> In StorageDatabase::getSegmentValue (yes, this method again(!)) we do
> a check on the precision, to see if the value is big enough to need
> special treatment:
> 
>         else if (field->precision < 19 && field->scale == 0)
>              {
>              int64 number = (signed char) (*ptr++ ^ 0x80);
> 
>              for (int n = 1; n < length; ++n)
>                  number = (number << 8) | *ptr++;
> 
>              if (number < 0)
>                  ++number;
> 
>              value->setValue(number);
>              }
>          else
>              {
>              BigInt bigInt;
>              ScaledBinary::getBigIntFromBinaryDecimal((const char*)
> ptr, field->precision, field->scale, &bigInt);
>              value->setValue(&bigInt);
>              }
> 
>          break;
> 
> This test is obviously wrong., what we want to test for is:
> 
> else if (field->precision <= 9 && field->scale == 0)
> 
> This will fix the problem.
> 
> Even better, we can avoid the test all together and treat all decimal
> keys as if they *may* have a precision greater than 9. This way there
> will be less code and we can avoid a cluttering 'if'. However, this
> will result in an additional function call or more (see the else
> clause above).
> What do you think? Am I allowed to remove the entire 'else if'?   :)

If think additional function call is not a problem and should be preferred
for reasons of simplicity and avoiding cluttering. Provided
ScaledBinary::getBigIntFromBinaryDecimal works correctly, which might be a
big "if". 

 
> Btw, when I am done with the fix for bug#40607, there will be some
> more rewrite in this area as well, but that is a different bug ...
> 
> 
> /Lars-Erik
> 
> [1]  -  http://dev.mysql.com/doc/refman/6.0/en/precision-math-decimal-
> changes.html
> 
> 
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Thread
Fix for bug#41582Lars-Erik Bjørk19 Dec
  • Re: Fix for bug#41582Hakan Kuecuekyilmaz19 Dec
    • Re: Fix for bug#41582Lars-Erik Bjørk19 Dec
  • RE: Fix for bug#41582Vladislav Vaintroub19 Dec
    • Re: Fix for bug#41582Lars-Erik Bjørk19 Dec
      • RE: Fix for bug#41582Vladislav Vaintroub19 Dec