On Sun, May 4, 2014 at 1:07 PM, Michael Haggerty <mhag...@alum.mit.edu> wrote:
> On 05/03/2014 10:12 PM, brian m. carlson wrote:
>> Many places throughout the code use "unsigned char [20]" to store object IDs
>> (SHA-1 values).  This leads to lots of hardcoded numbers throughout the
>> codebase.  It also leads to confusion about the purposes of a buffer.
>> Introduce a structure for object IDs.  This allows us to obtain the benefits
>> of compile-time checking for misuse.  The structure is expected to remain
>> the same size and have the same alignment requirements on all known
>> platforms, compared to the array of unsigned char.
> Please clarify whether you plan to rely on all platforms having "the
> same size and alignment constraints" for correctness, or whether that
> observation of the status quo is only meant to reassure us that this
> change won't cause memory to be wasted on padding.

It's not just about wasted padding. Some structs, like
ondisk_cache_entry, reflect on-disk format. Padding means breakage.
But I don't think this will be a big issue because we can detect if
padding happens, abort to force the user to complain, and deal with it
on case-by-case basis.
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