Re: [boost] Interest in a octet iterators library

From: Kimon Hoffmann (Kimon.Hoffmann_at_[hidden])
Date: 2007-08-08 13:38:08

Hi Kevin,

>> * The implementation should be endian invariant to make cross platform
>> digest checks feasible.
> 
> The message digest algorithms cannot know the layout of your data,
> i.e. is the data you're passing in a bunch of int32_t or int64_t, etc.
> or mixed types (which will be the case for many binary formats).
> However the implementation _is_ endian invariant in the sense that if
> you pass in the same data on big/low endian machines you will receive
> the same digest.

I'm sorry, of course it is endian invariant since it hashes sequences of
octets and therefor endianess is not an issue.

What I actually meant was, that in case someone would want to hash
custom types, like POD structs, a lot of mindless and error prone code
is needed. The most straightforward approach of casting the instance
into a array of chars is also the most flawed one, because of
uninitialized data in padding bytes and endianess, of course. So the
correct solution would be to build a character array by hand, converting
values to a defined byte order as necessary.
Since your library already provides iterator based hashing, octet
iterators would, easily allow hashing user-defined types, performing any
conversion that is needed on the fly.

Regards,
  Kimon