IMO the pragmatic approach would be to settle with one fp format and implement (more or less trivial) transformation functions to support the platforms that don't implement it natively. Picking IEEE754 standard would seem fine unless somebody can point out gaps preventing this from being able to convey features other formats can.

Going further, to accommodate the somewhat rare cases where IEEE754 would not be the best choice the library could support multiple representations and platform-specific transformations between them leaving the choice of the FP format used by the archive (which could be modified at any time using manipulators) to the programmer.

_
Michal Strzelczyk

Daryle Walker <darylew@hotmail.com>
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28/08/2008 10:13

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Subject	Re: [Boost-users] cross-platfrom binary serialization?

On Aug 27, 2008, at 4:38 PM, Bo Peng wrote: >> I have an alternate suggestion: what about continued fractions? >> Turn the >> floating point value into a list of integers. This works no >> matter what >> f.p. systems the source and destination use. You just need a >> portable >> integer serialization format. > > Then why cannot we use IEEE745 format for float serialization on > all systems? Because I don't think that the IEEE-754 internal format is as stable as you think it is. (Looking at Wikipedia's entries on IEEE-754 and 754r, there is a standard conceptual format, but problem is how do various implementations carry out the internal bit-wise format. Room for interpretation will doom your plan.) > 1. If a systems is IEEE745 compatible, serialize float numbers > directly. This will work 99.9% of the times, and will be very > efficient. > 2. If a system is not IEEE745 compatible, to serialize a float number, > we write the number as 32 or 64 continuous bits, in IEEE745 format, to > de-serialize a float number, we read the number in IEEE745 formats and > write in native float format. An intermediate string representation > can be used for the translations. The string or "direct" conversions may introduce rounding errors. > I mean, these continuous IEEE745 bits are equivalent to your "portable > integer serialization format", but will be much more efficient on > IEEE745 compatible systems. Is it worth potentially screwing 0.01% of your customers when you may not have to? -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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