Re: NSInteger vs int vs int32_t
Re: NSInteger vs int vs int32_t
- Subject: Re: NSInteger vs int vs int32_t
- From: vincent habchi <email@hidden>
- Date: Mon, 09 Jul 2012 20:54:32 +0200
On 9 juil. 2012, at 20:40, Greg Parker <email@hidden> wrote:
> On Jul 9, 2012, at 5:44 AM, Vincent Habchi <email@hidden> wrote:
>> Modern CPU do not enforce strict alignment for integer access. You can perfectly access a Dword (64 bits) at any address, even or odd. It is just more efficient to align 64-bits words at 8-bytes boundary, 32-bits at 4-bytes, etc. This contrasts with the old times: for example, on a 68000 processor, trying to access a 16-bit word at an odd address (e.g. move.w d0, (a0)+ with a0 odd) would result in a exception n°3 (address error).
>
> Some CPUs still enforce aligned integer access, such as the ARM CPUs in some iOS devices.
Oh, thanks for mentioning this. I was obviously thinking about Intel CPUs. I know very little about ARM. By the way, you can also access misaligned instructions on x86 processors I think, something that was not possible on 68000. If I remember correctly, the integer alignment enforcement was lifted on the 68030, which leaded to interesting hardware developments…
Vincent
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