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Subject: Re: [boost] [endian] Project not maintained
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2016-04-03 21:58:34

On 4/04/2016 02:21, Beman Dawes wrote:
> The new plan is to go ahead with an Endian proposal to the C++ committee.
> They have the expertise to know whether it is even possible to convert
> between big and little endian floating point in any useful (and
> non-dangerous) way.

If you have API that can take a void* or char* (or other
block-of-bytes-of-appropriate-size) and then reinterpret this as a
big-endian or little-endian float/double/longdouble (returning the
native representation), then this can work and is a useful function.
Similarly taking a native float/double/longdouble and writing it to a
block-of-bytes in a specified endian format.

If you have an API that takes a float/double/longdouble that was already
set with the "wrong" endian and you want to byteswap it, then this
cannot work and is a bad API. (This was the problem with the prior
version, IIRC.)

As a Boost.Endian library user, until the first style of API is
implemented you can work around it by doing endian swaps on unsigned
integers only, and using a bitwise_cast-equivalent to convert between
the floating-point values and unsigned integers of appropriate size.

(Although bitwise_cast is itself a debated topic, since doing it via
unions typically has better codegen but is technically UB, and doing it
without unions can get you into strict aliasing trouble if you're not

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