Re: [Gnash-commit] gnash ChangeLog libbase/utility.h server/charac...

[zou lunkai]

>
> > All of these rely on undefined behaviour. Conversion from float to an
> > integer is undefined behaviour if the float value cannot be represented
> > in the integral value after truncation (i.e. when the fractional value
> > has been removed).
> >
>

'undefined behaviour' only occurs when the 'double' number is out of
an integer's range in theory.  In practice, they are all 'defined' to
MSVC6, GCC3.4 and GCC4.1. I planed to add some tests to
testsuite/server for these simple functions. It's easy to test if any
compiler gives unexpected results.

>
>  Also you can't convert a double this way, as a double is 8 bytes, and on
> many systems an int is only 4 bytes still. The only way I know to really
> convert it is to separate the integer value and the fractional values and
> then round one way or the other.
>

I know that sizeof(double) == 8 and sizeof(int) == 4. But why it's
related? I do not expect an 'integer' to represent a 'double' without
loss.  Instead, I do need the loss. I need the truncation.

--zou

On 6/13/08, Rob Savoye <address@hidden> wrote:
> Benjamin Wolsey wrote:
>
> > All of these rely on undefined behaviour. Conversion from float to an
> > integer is undefined behaviour if the float value cannot be represented
> > in the integral value after truncation (i.e. when the fractional value
> > has been removed).
> >
>
>  Also you can't convert a double this way, as a double is 8 bytes, and on
> many systems an int is only 4 bytes still. The only way I know to really
> convert it is to separate the integer value and the fractional values and
> then round one way or the other.
>
>        - rob -
>
>
>
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