Re: float to int conversion

[Andrew Haley <aph at redhat dot com>]

On 04/22/2013 11:12 AM, Warlich, Christof wrote:
> ketmar wrote:
>> 0x7fffffc0 can'be exactly represented in float, 'cause there is some
>> bits occupied by exponent. so it is rounded so some other number, which
>> is unfortunately too big to be converted to int. therefore conversion
>> triggers undefined behavior.
> 
> Yes, that's what I suspected after I tried Andrew's example.
> 
>> change float to double and everything will be fine.
> 
> I guess that only shifts the problem to (much) higher numbers.
> 
> After all, this reminds be a bit of a hack lawver: A legal loophole
> shamelessly capitalizing upon ;-). At least, it violates the golden
> principle of "least surprise", being said to be an essential part of
> good software design.

What do you think the conversion should do in this case?  I find
the current behaviour to be the least surprising.

> Anyhow, as I really need to deal with such situations: Is there a way
> to catch such conversion errors without cluttering the code with checks
> that test if still being within the range of a conversion or not? Skimming
> the paper linked by David suggests that it should be possible to
> install trap handlers for this purpose. Does anyone know how to do this
> with gcc?

Just define your own conversion function.  Any program that tries to
convert an out-of-range value and then uses the result is buggy anyway.

Andrew.