From: Young Hyun <youngh@...>
Date: 2006-09-23T02:51:34+09:00
Subject: Re: 64-bit integers in network byte-order

On Sep 22, 2006, at 8:56 AM, Francis Cianfrocca wrote:

> On 9/22/06, Francis Cianfrocca <garbagecat10@gmail.com> wrote:
>> All,
>> does Ruby have a way to convert 64-bit integers to and from network
>> order in a platform-independent way?
>>
>> For 32-bit ints, I can use [value].pack("N"). The conversion operator
>> for 64-bit ints ("Q") doesn't have a network-order variant. (I assume
>> this is because the underlying byte-order converters (htons/htonl)  
>> don't
>> have a 64-bit version on 32-bit platforms.)
>>
>
> Thanks, guys. I sort of figured I'd have to hack it. Ara, I thought of
> your approach (detecting endian-ness locally) but really hoped I could
> avoid it! (Ghostbusters: "I feel so funky.")
>
> Combining your approach with Dave's (and passing both through several
> additional processing stages), I end up with:
>
> #--------------------------------------
> BigEndian = [1].pack("s") == [1].pack("n")
>
> def htonq value
>  BigEndian ? val : ([val].pack("Q").reverse.unpack("Q").first)
> end
> #--------------------------------------
>
> and of course ntohq is identical to htonq.

Funny, I wrote almost exactly the above code just recently.  But, it  
may not be necessary.  Depending on your situation, you might  
consider using the "w" (BER-compressed integer) packing directive  
instead.  It guarantees that arbitrarily long integers are stored in  
a standard way (big endian).  The caveats are (1) it produces  
variable-length packed strings and (2) it only supports positive  
integers.  However, because BER-compressed integers are self- 
describing, in the sense that you can determine when you've reached  
the end of the encoded string, you could get around the first  
limitation (if it proves to be a limitation for your usage scenario)  
by left justifying the BER-compressed integer in a fixed field.  For  
my situation, I just changed the definition of my wire protocol to  
support variable-length "w"-encoded strings and didn't bother left  
justifying.

  --Young