Re: [GD-General] meaning of sizeof(int) on all plateform

[Evan R. <ev...@en...>]

From: Evan Robinson <ero...@en...>
Date: Thu Jun 26, 2003  2:36:27 PM US/Pacific
To: gam...@li...
Subject: Re: [GD-General] meaning of sizeof(int) on all plateform


On Thursday, June 26, 2003, at 01:12 PM, Lagarde S=E9bastien wrote:

> no confusion here,
> Following suestion here are purelly curiosity:
> =A0
> i precise the question:
> =A0
> if you have a 32 bit architecture (pentium)
> if you want make fast arithmetic operation, you
> must work with type which have a size of 32bits.
> These type have the same size of a register and the
> arithmetic operation can be optimize...
> typically, this is type "int"
> =A0
> on a 64 bit architecture (itanium)
> register are 64 bit and int are 64bit too
> =A0
> so if you have a program which perform the following code:
> =A0
> // imaginary define
> // the goal of this define is to have s32 on 32bits
> #ifdef __32Bit__
> typedef int s32
> #else // __64bit__
> typedef short u32=A0 // just for exemple
> #endif
> =A0
> void add(s32 a1, s32 a2)
> {
> =A0=A0=A0 return a1 + a2;
> }
> =A0
> the performance can be poor on a 64bit architecture because we are not
> in the native size of the register
> =A0
> if we have this code
> =A0
> void add(int a1,=A0int a2)
> {
> =A0=A0=A0 return a1 + a2;
> }
> =A0
> no problem, cause "int" is native to the architecture

Not necessarily.  "int" is a logical construct *of the compiler*, not=20
*of the platform*.  You *hope* that your compiler vendor has made int=20
the most efficient size for general purpose integer math.

> it is my imagination, I'am in the wrong way ?
> =A0
> another question, is sizeof(int) =3D=3D sizeof(void*) ?
> sizeof(void*) must be : size of memory bus address
> so sizeof(int)....

Once again, not necessarily.  "void *" is a logical construct "of the=20
compiler*.  You would expect a void * to be as many bits as necessary=20
to express the entire memory footprint of the computer architecture,=20
but there is no reason why it couldn't be either larger or smaller,=20
depending upon the compiler vendor.  A straightforward (if evil)=20
example would be the segmented 8088 architecture, where the base memory=20=

footprint was 1024K, but the RAM footprint was generally 640K, and full=20=

pointers were 32 bits (16 bit segment, 16 bit offset).  A 20-bit=20
pointer would have sufficed for the base memory footprint, but could=20
not have properly expressed all segment:offset pairs


If you are trying to make sure that your code will run equally=20
efficiently on *all platforms* and *all compilers*, you are (probably=20
wasting your time) probably best off relying on "int" and "void *" and=20=

not worrying about how they match to the platform until you have a=20
specific platform and compiler combination in mind.

> --------------------------
> Lagarde S=E9bsatien
> Neko entertainment
> Junior programmer
>
> ----- Original Message -----
> From: Mick West
> To: gam...@li...
> Sent: Thursday, June 26, 2003 8:48 PM
> Subject: RE: [GD-General] meaning of sizeof(int) on all plateform
>
> 128 bits would give you 16 bytes, not 32.
> =A0
> On the PS2 an int is generally 32 BITS,=A0 (4 bytes), which is maybe=20=

> where the confusion arose.
> =A0
> Mick
>
>
> -----Original Message-----
> From: gam...@li...=20
> [mailto:gam...@li...] On Behalf Of=20=

> Gareth Lewin
> Sent: Thursday, June 26, 2003 11:42 AM
> To: gam...@li...
> Subject: RE: [GD-General] meaning of sizeof(int) on all plateform
>
> sizeof(int) =3D size of integer value. As defined by the compiler=20
> vendor. There is no "Correct" way to set the size of int.
>
> -----Original Message-----
> From: Lagarde S=E9bastien [mailto:Lag...@wa...]
> Sent: 26 June 2003 19:36
> To: gam...@li...
> Subject: [GD-General] meaning of sizeof(int) on all plateform
>
> Hello all,
> I have some problem to define what represent sizeof(int).
> =A0
> IMO sizeof(int) =3D=3D memory bus address width
> =A0
> but on platforme like PS2, you have a bus of 128 and sizeof(int) =3D=3D =
32.
> =A0
> i have seen elsewherre that sizeof(int) =3D=3D size of a register.
> =A0
> Is someone have some information on this point ?
> thanks
> -------------------------------
> Lagarde S=E9bastien
> Neko entertainment
> Junior programmer
> =A0
>
>
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