Re: [Boost-users] Convert big endian to little endian (floating point values)

Subject: Re: [Boost-users] Convert big endian to little endian (floating point values)
From: Martin Vymazal (martin.vymazal_at_[hidden])
Date: 2015-12-08 16:14:21

On 2015-12-08 19:40, Aaron_Wright_at_[hidden] wrote:
>> From: Martin Vymazal <martin.vymazal_at_[hidden]>
>> Hello,
>> 
>> I am trying to convert a floating point value from big endian to
> little
>> endian, but the code below does not compile:
>> 
>> double x = 10.0;
>> 
>> const double x_big_endian = boost::endian::native_to_big(x);
>> boost::endian::native_to_big_inplace(x);
> 
> Be very careful how you swap floats. They aren't like integer data
> types where the swapped representation can fit nicely into the same
> type. Not all swapped floats are valid floats, and you'll find that
> the bits will be messaged into a valid float, thus changing your value
> without telling you. You can only swap a float into an integer. You
> can't swap a float into a float.

Hi,

  ok, here's the whole story. We have a code that computes some data, 
compresses them through zlib and saves as binary. We also use our own 
utility to postprocess the compressed file and convert it to 
human-readable format.

  What happened recently is that the code ran on a big-endian machine and 
since zlib preserves the endian-ess of the data, it  generated a binary 
with big-endian doubles. We would like to have the possibility of 
bringing that file on a little-endian machine (say user's laptop) and 
postprocess there, instead of doing everything on the big-endian 
machine. Do you have an alternative suggestion how to approach this 
problem? Let's assume that writing the output data in any other format 
than the current one is not possible.

I am also still interested in knowing whether boost (1.59) supports 
conversions between endian representations of floating-point values.

Martin