code:
# float f = 1.2e-3;
# float a = 12.0;
# float b = 10000.0;
# float c = a/b;
# assert(f == c);
# assert(f == a/b);

The first assertion passes but the second fails.

test case: svn://svn.kuehne.cn/dstress/run/float_literal_dec_02.d

Thomas Kuehne wrote:

> code:
> # float f = 1.2e-3;
> # float a = 12.0;
> # float b = 10000.0;
> # float c = a/b;
> # assert(f == c);
> # assert(f == a/b);
> 
> The first assertion passes but the second fails.
> 
> test case: svn://svn.kuehne.cn/dstress/run/float_literal_dec_02.d

This is because the first comparison uses float while the second uses real; the float truncates some rounding error in the division that is preserved for the comparison in the second assert.  This is a natural effect of type promotion.

The real bug is that this doesn't work properly:

   assert(f == cast(float) (a/b));

This should cause the value to be truncated, but it doesn't.

You can cause your code to succeed if you eliminate the rounding error.  Divide by a power of 2 instead:

   float f = 0.01171875;
   float a = 12.0;
   float b = 1024.0;

This will then work.  That could probably be considered a correct test of the language, as D depends on IEEE being present.

Burton Radons schrieb:
> > code:
> > # float f = 1.2e-3;
> > # float a = 12.0;
> > # float b = 10000.0;
> > # float c = a/b;
> > # assert(f == c);
> > # assert(f == a/b);
> >
> > The first assertion passes but the second fails.
> >
> > test case: svn://svn.kuehne.cn/dstress/run/float_literal_dec_02.d
>
> This is because the first comparison uses float while the second uses real; the float truncates some rounding error in the division that is preserved for the comparison in the second assert.  This is a natural effect of type promotion.
>
> The real bug is that this doesn't work properly:
>
>     assert(f == cast(float) (a/b));
>
> This should cause the value to be truncated, but it doesn't.

Thanks for the fix - guess I have to read a little about IEEE :)

Thomas

Thanks for the time and effort the two of you are putting into making 'D' an even better tool.

"Burton Radons" <burton-radons@smocky.com> wrote in message news:ckj8ps$2te8$1@digitaldaemon.com...
> Thomas Kuehne wrote:
>
> > code:
> > # float f = 1.2e-3;