Byte Order Swapping Function

[Jonathan M Davis]

On Thursday 14 July 2011 06:27:47 Andrei Alexandrescu wrote:
> On 7/14/11 5:51 AM, Regan Heath wrote:
> > That's my point. I need 8/16/32/64/128 bit versions and it really would
> > be better if there were general variants. My version are less than
> > optimal, but do use intrinsics where possible. Someone else can do a far
> > better job than I, and it really should be done once, by that person.
> > Surely we have the infrastructure for someone to add this to phobos? If
> > something this simple can't or won't be done, what hope do we have!?
> 
> I think we should have these functions in std.bitmanip:
> 
> T toBigEndian(T)(T val) if (isArithmetic!T || isSomeChar!T);
> T toLittleEndian(T)(T val) if (isArithmetic!T || isSomeChar!T);
> T bigEndianToNative(T)(T val) if (isArithmetic!T || isSomeChar!T);
> T littleEndianToNative(T)(T val) if (isArithmetic!T || isSomeChar!T);
> 
> That means all characters, all integers, and all floating point numbers.
> The implementations would opportunistically use intrinsics and other
> specialized means.
> 
> The documentation should specify the relationship to htonl and ntohl.
> 
> If there's a need for converting endianness of larger buffers, we might add:
> 
> ubyte[] toBigEndian(ubyte[] val);
> ubyte[] toLittleEndian(ubyte[] val);
> ubyte[] bigEndianToNative(ubyte[] val);
> ubyte[] littleEndianToNative(ubyte[] val);
> 
> They'd use std.algorithm.reverse internally as needed.
> 
> It's a sweet piece of work. Anyone have the time to prepare a pull request?

I decided to take a crack at it, and it seems to be going pretty well, except 
that I can't seem to get the floating point values right. Somehow, when I 
compare a floating point value with the same value except that it's had its 
endianness swapped twice, they return true for is but false for ==, which 
makes absolutely no sense to me. There's obviously either something that I 
don't understand about floating point values (or the relationship between is 
and ==) or a bug in dmd. It'd be one thing if I couldn't get the values to 
reverse properly, but when they're equal according to is but not ==, I have no 
idea how that could even be possible.

- Jonathan M Davis