Re: Any examples of Byte Ordering Functions

[chris <spamoff.danx@ntlworld.com>]

Hi,

I'm trying to implement reading 16 bit words from a stream with a given 
endianess (that is the endianess of the items in the stream is known), 
and think the following implementation is independant of the actual 
order of bytes in a word variable.  Am I right?  It'd be nice not to 
have two versions of this code and have to take different cpu 
architectures into account at compile time!  Can I expect the compiler 
(gnat say) to optimise multiplication of modular types by *powers of 
two* to shift lefts (and divisions by powers of two to shift rights)?


type Byte is mod 2**8;
for Byte'Size use 8;

type Word is mod 2**16;
for Word'Size use 16;


bytes in stream:  a b c d e f g h

Read Big Endian encoded Word:

    W := a * 256 + b;

Read Little Endian encoded Word:

    W := b * 256 + a;



Cheers,
Chris