Re: [Algorithms] Byte Swapping

[Jens A. <jAy...@ne...>]

Tom Hubina:
> Jens Ayton:
>> Tom Hubina:
>>>
>>> I can do the obvious method, but I was wondering if anyone
>>> have any cool/fast code snippets for byte swapping integers
>>> and floats?
>>
>> Depends on the platform. PowerPCs have "load word byte-
>> reversed indexed" (lwbrx) and "load halfword byte-reversed
>> indexed" (lhbrx) instructions, for instance.
> 
> Since that happens to be my platform, perhaps you would have
> some routines handy that work in Codewarrior for the Mac that
> make those calls to reverse the bytes I'm loading?

These instructions are available as intrinsics. If you have an aligned
array theLittleEndianArrayOfLongs of wrong-endian longs, this:

long theLong = __lwbrx(theLittleEndianArrayOfLongs, n);

is equivalent to

long theLong = theBigEndianArrayOfLongs[n];

for right-endian data. Similarly, you can use

short theShort = __lhbrx(theLittleEndianArrayOfShorts, n);
                    ^
Note the "w" vs. "h" as marked.

-- 
Jens Ayton