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64 bit check?

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  64 bit check? bob <bob@coolfone.comze.com> - 2013-04-02 13:58 -0700
    Re: 64 bit check? Ian Collins <ian-news@hotmail.com> - 2013-04-03 10:09 +1300
    Re: 64 bit check? Robert Wessel <robertwessel2@yahoo.com> - 2013-04-03 01:14 -0500
    Re: 64 bit check? Jongware <jongware@no-spam.plz> - 2013-04-03 16:42 +0200

#3217 — 64 bit check?

Is this a foolproof way to check if your code is running in 64 bit mode?

int pointer_size = sizeof(int*);
boolean sixty_four_bit = (pointer_size==8) ? true : false;

Thanks.

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#3218

bob wrote:
> Is this a foolproof way to check if your code is running in 64 bit mode?
>
> int pointer_size = sizeof(int*);
> boolean sixty_four_bit = (pointer_size==8) ? true : false;

Define a constant at compile time based on the compiler's built in flags.

-- 
Ian Collins

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#3219

On Tue, 2 Apr 2013 13:58:38 -0700 (PDT), bob <bob@coolfone.comze.com>
wrote:

>Is this a foolproof way to check if your code is running in 64 bit mode?
>
>int pointer_size = sizeof(int*);
>boolean sixty_four_bit = (pointer_size==8) ? true : false;


Nope.

What if chars are bigger than eight bits?

What if addresses are not 64 bits?  While you might have difficulties
finding exactly such systems, example of that sort of oddness have
existed.  Consider the memory models for 16 bit x86 code.  Pointers
could be either 16 or 32 bits in length, and code and data pointers
could be different sizes.  Some implementations have much additional
data in the pointers, for example, on some AS/400 implementations,
despite being a 48 or 64 bit machine, pointers might be up to 64 bytes
long.

Or how do you classify programs that run using the x32 ABI, where the
code is x86-64, but only 32 bits of pointers are stored?

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#3220

On 02-Apr-13 22:58 PM, bob wrote:
> Is this a foolproof way to check if your code is running in 64 bit mode?
>
> int pointer_size = sizeof(int*);
> boolean sixty_four_bit = (pointer_size==8) ? true : false;

If your compiled code is running on a 64-bit CPU emulator (say, in 
current CPU design software; or, in 20 years time, to emulate vintage 
systems), should it return 'true' or 'false'? I think either answer 
might be possible ...

Anyway, as has been pointed out, the question is irrelevant because you 
have to *compile* it for '64-bit mode' OR for '32-bit mode'. So -- with 
all #defines et cetera resolved -- the actual code that gets compiled 
boils down to

boolean isSixtyFourBit (void)
{
   return true;
}

[Jw]

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