Re: where to discuss problems with IEEE 754 standard on x86 architecture?

[Tim Prince <tprince@myrealbox.com>]

Petr Savicky wrote:
>> You were using -mfpmath=387 (possible as the default), and that uses
>> Intel native arithmetic, which is NOT standard IEEE 754 double, but
>> an extended format.
>>
>> If you use -mfpmath=sse, you will get what you expect.
>>
>>     
> Thank you for your reply. This explains the problem.
>
> However, solving the problem seems to be harder.
> I tried "gcc -mfpmath=sse", but obtained the warning:
>  SSE instruction set disabled, using 387 arithmetics.
>
> gcc version: 3.3.3
> uname -m -p -i: i686 i686 i386
> /proc/cpuinfo:
>   vendor_id   : GenuineIntel
>   cpu family  : 15
>   model       : 2
>   model name  : Intel(R) Xeon(TM) CPU 2.80GHz
>
> I obtained the same on another computer with
> gcc version: 4.1.0
> uname -m -p -i: i686 i686 i386
> /proc/cpuinfo:
>   vendor_id   : GenuineIntel
>   cpu family  : 6
>   model       : 8
>   model name  : Celeron (Coppermine)
>
> man gcc says: For the i386 compiler, you need to use -march=cpu-type, -msse or -msse2 switches
>                to enable SSE extensions and make this option effective.
> The choices for cpu-type are the same as for -mtune. 
> -mtune=cpu-type has possible values itanium, itanium1, merced, itanium2, and mckinley
>    none of which seems to fit my computers.
>
> With "gcc -mfpmath=sse -msse" I obtained no warning/error, but the program
> behaves in the old wrong way.
>
> So, I think that SSE is not available on my computers. Is this correct?
>
>   
Why didn't you follow the advice you quoted? 
gcc -march=pentium4 -mfpmath=sse
When you compile code for pentium2, of course SSE is not available to 
the compiler.