[fpc-pascal] math round vs banker's round
mschnell at lumino.de
Wed Aug 14 09:55:11 CEST 2013
On 08/14/2013 09:38 AM, Sven Barth wrote:
> - 0.5 does not always have a direct representation as a floating point
> value and thus internally it might be 0.4999999 or something like that
> and thus it will be rounded to 0.4 (see also
> http://bugs.freepascal.org/view.php?id=24374 )
AFAIU, in hardware / memory, the binary representation of -0.5 is
(sign * mantissa * 2 ** exponent ) = (-1) * 0.5 * 2 ** 1
so this seems to be "exact"
Maybe the compiler does not calculate exactly this value when doing the
constant "-0.5". I don't consider this a problem, as IMHO, in fact any
attempt to rely on an exact value of a floating point number is erroneous.
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