Re: Calculator problem on ARM board

[Bill Gatliff <bgat@xxxxxxxxxxxxxxx>]

kartikay Malhotra wrote:
> Hello All,
> 
> I am facing a problem. I have a calculator application, which has 14 bit
> screen. When I add two numbers, number1 += number2, where both number1 and
> number2 are double, and one of the numbers is very large, and the other
> number is small, I get an error in result.

Welcome to the world of floating-point math.  High dynamic range, but depending
on where you are at magnitude-wise the precision can be pretty low.

> For example, 10000000000000 + 1 gives 1e+13, instead of 10000000000001. This
> is because the result string  is actually 10000000000000.99.

Yep.  That's a big number, and you don't have the precision to represent it as
accurately as you want.

> 
> Is there a problem in the compiler, or is double precision arithmetic
> incorrect? The same application complied for x86 gives no error.

Well, if both systems conform to ieee695 then the results should be identical.
Is one machine soft-float and the other using an FPU?  Note that for ARM, the
FPU might be emulated by kernel code, so you are actually using a different
runtime implementation than x86.  For apples-to-apples comparisons, use
soft-float everywhere.


HTH,


b.g.
-- 
Bill Gatliff
bgat@xxxxxxxxxxxxxxx

-------------------------------------------------------------------
List admin: http://lists.arm.linux.org.uk/mailman/listinfo/linux-arm
FAQ:        http://www.arm.linux.org.uk/mailinglists/faq.php
Etiquette:  http://www.arm.linux.org.uk/mailinglists/etiquette.php