Byte Order Swapping Function

[Andrei Alexandrescu]

On 7/16/11 3:39 AM, Jonathan M Davis wrote:
> 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

Just paste the code here.

Andrei