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Re: little-endian

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On 11/18/2012 2:13 AM, Dmitry A. Kazakov wrote:
> On Sun, 18 Nov 2012 15:17:51 +1300, Ian Collins wrote:
>
>> On 11/18/12 11:22, BGB wrote:
>>>> Some more valid criticisms of the hton*/ntoh* functions are that they
>>>> only support one byte order on the "network" side, support only a
>>>> couple of sizes, and only support unsigned values.
>>
>> long long version are a simple extension.
>
> Nope. It could be middle-endian.
>
>> The signed or unsigned nature
>> of the type isn't relevant for byte ordering.
>
> How so? Byte ordering is about encoding things into a byte stream. Signed
> integers must be encoded too.
>

yeah. signed vs unsigned storage is an issue all to itself.

>>> far more common I think is to implement file-readers more like:
>>> int MyFile_ReadInt32LE(FILE *fd)
>>
>> The reason for using the common byte ordering functions is to avoid
>> having to care about the ordering on the wire (or in a file).
>
> There are far more types of objects than unsigned integers. When
> implementing an application protocol on top of some octet or bit stream
> these must be encoded and decoded (serialized/deserialozed) too. There is
> nothing special in unsigned integers.
>
> Usage of functions like hton* should be depreciated unless the protocol
> specification explicitly states that the given unsigned integer object is
> in the "network" format as implemented by hton*.
>

yeah.

hton* and ntoh* make sense when dealing with socket-related stuff, but 
don't make nearly as much sense when dealing with file-formats.


typically, the layout of data within a file-format is a fairly important 
part of the file-format, and not really all that consistent between one 
file format and the next, and sometimes you are lucky even if all of the 
members within the same file-format have the same ordering.

worse-still is fileformats where the designer thought about being clever 
and defining the endianess as "whatever was convenient for the writer 
program", which basically amounts to the reader having to keep track of 
a flag for which endianess the file was stored in.


> It is always cleaner to provide a fair implementation of the protocol,
> which could be done in a portable way as BGB described. Which is really the
> recommended way. A rare exception might be when you have a library that
> already implements the protocol layer of interest completely.
>

yeah.

or when dealing with file-formats.

with explicit reader/writer functions, it is also fairly straightforward 
to write functions to deal with pretty much any types the format may 
include, including things like variable-length integers, and values of 
types which don't necessarily start/end on a byte-boundary (common with 
bitstreams).

typically, any structures used are kept purely internal, and the exact 
layouts and types of data present in a file are not tied to the structs 
(and how the particular compiler and target has decided that they should 
be laid out), and it isn't really that much more effort to read/write 
all of the members directly via function calls, than it is to read/write 
structs and swizzle the values afterwards.


other times (depending on how the format is used), it may make sense to 
use structs, but simply define all of the members as byte-arrays, and 
then use functions to read/write the values from the structures (this 
makes things like type-alignment largely a non-issue).

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little-endian bob <bob@coolfone.comze.com> - 2012-11-15 13:45 -0800
  Re: little-endian JJ <jaejunks@glegooilma-swapit.com> - 2012-11-15 23:33 +0000
  Re: little-endian bob <bob@coolfone.comze.com> - 2012-11-16 10:38 -0800
    Re: little-endian "Pascal J. Bourguignon" <pjb@informatimago.com> - 2012-11-16 23:32 +0100
      Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-16 21:17 -0600
        Re: little-endian "Pascal J. Bourguignon" <pjb@informatimago.com> - 2012-11-17 10:26 +0100
          Re: little-endian "BartC" <bc@freeuk.com> - 2012-11-17 11:38 +0000
            Re: little-endian "Pascal J. Bourguignon" <pjb@informatimago.com> - 2012-11-17 13:56 +0100
              Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-17 11:58 -0600
            Re: little-endian Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-17 19:35 +0000
              Re: little-endian "BartC" <bc@freeuk.com> - 2012-11-17 19:50 +0000
          Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-17 11:30 -0600
            Re: little-endian Ian Collins <ian-news@hotmail.com> - 2012-11-18 09:28 +1300
              Re: little-endian Robert Wessel <robertwessel2@yahoo.com> - 2012-11-17 14:48 -0600
                Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-17 16:22 -0600
                Re: little-endian Ian Collins <ian-news@hotmail.com> - 2012-11-18 15:17 +1300
                Re: little-endian "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-11-18 09:13 +0100
                Re: little-endian Ian Collins <ian-news@hotmail.com> - 2012-11-18 21:33 +1300
                Re: little-endian "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-11-18 10:15 +0100
                Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-18 03:03 -0600
                Re: little-endian "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-11-18 10:29 +0100
                Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-18 12:50 -0600
  Re: little-endian Robin Vowels <robin.vowels@gmail.com> - 2012-11-22 04:49 -0800
    Re: little-endian Jongware <jongware@no-spam.plz> - 2012-11-23 15:22 +0100
      Re: little-endian pacman@kosh.dhis.org (Alan Curry) - 2012-11-25 19:39 +0000
        Re: little-endian Jongware <jongware@no-spam.plz> - 2012-11-26 12:01 +0100
          Re: little-endian "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-11-26 14:02 +0100
            Re: little-endian Jongware <jongware@no-spam.plz> - 2012-11-26 15:34 +0100
              Re: little-endian "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-11-26 17:03 +0100
              Re: little-endian Robert Wessel <robertwessel2@yahoo.com> - 2012-11-26 17:44 -0600
                Re: little-endian Robin Vowels <robin.vowels@gmail.com> - 2012-11-28 23:43 -0800
                Re: little-endian Robert Wessel <robertwessel2@yahoo.com> - 2012-11-29 22:46 -0600
          Re: little-endian BGB <cr88192@hotmail.com> - 2012-11-26 08:30 -0600
        Re: little-endian Robin Vowels <robin.vowels@gmail.com> - 2012-11-28 23:45 -0800

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