[fpc-pascal] Writing floating points to steams

Mark Morgan Lloyd markMLl.fpc-pascal at telemetry.co.uk
Wed Jan 13 10:40:01 CET 2016


Torsten Bonde Christiansen wrote:
> On 2016-01-13 10:06, Mark Morgan Lloyd wrote:
>> Serguei TARASSOV wrote:
>>> On 13/01/2016 08:47, fpc-pascal-request at lists.freepascal.org wrote:
>>>> On 2016-01-12 10:45, Torsten Bonde Christiansen wrote:
>>>>> Since TStream doesn't have any native WriteFloat/Double and the likes,
>>>>> some conversion is needed - but what is a good strategy for this?
>>> Depends on size constraints.
>>> In the simple case you should convert float to locale-independent 
>>> string value (no spaces, no commas separators) then write it.
>>> If the size does matter, you may convert float to corresponding byte 
>>> array then write it.
>>
>> Can I ask a naive question here please: does a binary stream store 
>> endianness anywhere? In other words, is there any indication that 
>> something running on ARM is about to get into trouble by reading 
>> something written by (big-endian) MIPS?

> Not that I'm aware of - i would think of it as a stream of bytes. 
> Endianess is defined by the CPU not by the file.

Thanks, I assumed that was the case but thought it worth checking.

I suppose that one could stream variants, i.e. the enumeration saying 
what one was followed by a value.

>> Should writing binary floating point to a stream note that it's IEEE 
>> format, just in case anybody ever tries to process it on a platform 
>> that supports alternatives?
>>
> It would be great if storing floating point could be in IEEE, to have a 
> standard as reference.

I'm not at all sure about this, but I think I've seen something that 
suggested that byte ordering in external representations was covered by 
the standard.

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]


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