On Wednesday, September 05, 2007 Simon Davies wrote:
> [...]
> This resolves down to calling a function vxprintf, which has the following
> line:
> while( realvalue>=10.0 && exp<=350 ){ realvalue *= 0.1; exp++; }
> When this line is reached, realvalue has value 98926650.5 and exp value 0.
> realvalue then goes the following values during the loop:
> 9892665.0500000007
> 989266.50500000012
> 98926.650500000018
> 9892.6650500000032
> 989.26650500000039
> 98.926650500000051
> 9.8926650500000051
> exp finishes at 7
> Note the 'error' added in by the successive multiplications is 0.000000051
> [...]
> One wonders why XP/VC++ produces such a large error in its floating
> point manipulations that appears to be avoided by other compilers.
...probably because VC++ uses 64 bits for long double (53 bit
mantissa) whereas gcc uses 96 bits (64 bit mantissa). Note that
realvalue above is declared as LONGDOUBLE_TYPE (long double).
http://msdn2.microsoft.com/en-us/library/9c3yd98k(VS.80).aspx
http://msdn2.microsoft.com/en-us/library/9cx8xs15(vs.80).aspx
e
--
Doug Currie
Londonderry, NH, USA
-----------------------------------------------------------------------------
To unsubscribe, send email to [EMAIL PROTECTED]
-----------------------------------------------------------------------------
