Re: Range of 32 bit values
Re: Range of 32 bit values
- Subject: Re: Range of 32 bit values
- From: Luigi Castelli <email@hidden>
- Date: Mon, 9 Apr 2007 11:58:54 -0700 (PDT)
Hey guys,
first of all, thanks to all who replied.
Here is the problem:
the casting with wrapping is an optimization trick that the algorithm
uses.
So adding an instruction (or several) by using fmod() really defeats
the purpose.
Also, I cannot use only integers. The parameters before casting must be
floats.
These are the restriction that I have to deal with.
So my question remains as if there is a way to make the range of an
integer wrap after casting or if it's an operation entirely dependant
on hardware and the programmer has no control over it.
- Luigi
--- Greg Guerin <email@hidden> wrote:
> Luigi Castelli wrote:
>
> >I multiply big float values and - after being appropriately cast -
> >assign them to the above variable.
> >
> >Example:
> >
> >int value = (int)(32768. * 65536.) // (and bigger)
> >
> >I just so happens that when the result of the multiplication exceed
> the
> >size of the value that a 32 bit int type variable is able to
> represent
> >the value is clipped to -2147483648. I have noticed that the cast
> >(either explicit or implicit) is what causes the value to be
> clipped,
> >because if I cast to a bigger value (i.e. 64 bit) then the value is
> >wrapped until the 64 bit maximum is reached. Then the value is
> clipped
> >again.
> >
> >In any case for the algorithm I am developing I would like the int
> >value to be wrapped, not clipped. I would like after reaching the
> >value's maximum limit to go back and start again from its minimum.
>
> This seems like a simple answer: don't use float arithmetic.
> Only use operands that are 32-bit ints, not floats.
>
> You might also look into the Intel-specific behavior of casting
> floats to
> ints (overrange type-narrowing conversions). If CodeWarrior-compiled
> code
> wrapped around, it may be a side-effect of the CPU arch (PPC), and
> not at
> all related to CW vs. Xcode. As I vaguely recall, these kinds of
> conversions are unspecified by the C spec, but you really should
> check a
> spec, or just use ints.
>
> -- GG
>
>
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