[Bf-committers] 64 bits migration, windows/unix

[Ton Roosendaal]

Hi,

Sorry, these SDNA notes missed one counting hint. Just pretend pointers  
to be always 8 bytes long and it goes fine. Meaning, in 32 bits systems  
a three pointer struct will be paddingless. :)

But mind the rule "pointers have to be '8 byte aligned', so don't do  
this;

struct temp {
	int a;
	int *b;
};

Nor do this;

struct temp1 {
	int a;
	struct temp b;
};

The bSoundActuator goes fine, in 32 bits code it's 4 aligned all, in 64  
bits it's 8 aligned. :)

-Ton-


On 1 May, 2005, at 7:47, Ted Schundler wrote:

> On the 64 bit issue, what is the preffered method for dealing with
> padding? (Sorry if this was addressed somewhere already and I missed
> it)
> Blender3D.org's blurb on sdna structs says "structures are always
> multiples of 8 bytes in size", But if you have an odd number of
> pointers, in the struct, there's no guarantee of that.
>
> For instance, the bSoundActuator here (just picked on somewhat at
> random looking for padding examples):
> http://astro.scu.edu/~ted/oss/blender/bf-dox/d3/dfb/ 
> DNA__actuator__types_8h-source.html#l00064
> On a 32-bit architecture it is 64-bit aligned, but on 64-bit, with a
> 64-bit pointer, it isn't.
>
> Should such structs have an extra pointer pad variable just in case?
> Or should it have an extra 4 bytes, so on 32-bit platforms, it is at
> least 32-bit aligned, and 64-bit aligned on 64-bit platforms.
>
>
> Ted
>
> On 4/30/05, Ton Roosendaal <ton at blender.org> wrote:
>> Hi,
>>
>> We'll have to define the Blender standard for migrating to 64 bits for
>> all platforms... unfortunately the unix and windows worlds haven't
>> adopted the same standard...
>>
>> Check this diagram;
>> http://developer.apple.com/macosx/images/lp64compare.gif
>>
>> The key difference is that;
>>
>> - Windows keeps the "long" 32 bits in all cases, for unix it is 32 or
>> 64 bits.
>> - Windows doesn't have a "long long" (int64 instead).
>>
>> With Blender's unix origins - already tested for 32/64 bits in the  
>> past
>> - it would be simplest to investigate if we can typedef/define the
>> Windows version to follow the LP64 standard.
>> If we can do that, no further #ifdef exceptions are needed to patch  
>> our
>> code to be 32/64 bits compliant for all platforms.
>>
>> So, I would like a Windows 64 bits developer to check on the  
>> following;
>>
>> 1) Patch BLI_winstuff.h
>>
>> Something like this could work: (blenloader/intern/genfile.c uses it)
>>
>> #ifdef WIN32
>> typedef long long __int64;
>> #endif
>>
>> #ifdef WIN64
>> typedef long long __int64;
>> typedef long __int64
>> #endif
>>
>> One note though... the BLI_winstuff.h is only included in the
>> blender/source/ tree, not for our blender/intern/ and blender/extern/
>> libraries. These each have to be checked on 32/64 issues as well.
>>
>> 2) Cleanup of platform #defines
>>
>> We now already use a mix of WIN32 and _WIN32 to patch OS specific  
>> code,
>> this is in all cases not 32 bits related, so we need a new generic
>> define.
>>
>> I hope Microsoft / Cygwin has another standard already. This better  
>> not
>> gets patched in the BLI_winstuff.h, since we also have an intern and
>> extern libraries to take care of.
>>
>> 3) Verifying DWORD referrals
>>
>> In the Blender code are a couple of windows-only functions or C files.
>> Check the MSDB website for the porting guides for 64 bits, with  
>> several
>> notes on proper 32/64 bits code.
>>
>> -Ton-
>>
>> ---------------------------------------------------------------------- 
>> --
>> --
>> Ton Roosendaal  Blender Foundation ton at blender.org
>> http://www.blender.org
>>
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------------------------------------------------------------------------ 
--
Ton Roosendaal  Blender Foundation ton at blender.org  
http://www.blender.org