On Fr, 2008-12-19 at 11:32 +0100, Lars-Erik Bjørk wrote:
> 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'? :)
>
I recall that we had some problems with decimal > 19. Like
http://bugs.mysql.com/bug.php?id=28044
http://bugs.mysql.com/bug.php?id=26468
Please check those tests, whether your fix introduces a regression or
not.
> 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
>
>
Best regards,
Hakan
--
Hakan Küçükyılmaz, Senior Software Engineer DBTG/MySQL +49 160
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