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

Subject: Re: [Boost-users] cross-platfrom binary serialization?
From: Nat Goodspeed (nat_at_[hidden])
Date: 2008-09-27 09:41:07

I do understand that this issue has already been debated to the point of 
a new implementation. I just want to ask about a side point I didn't 
quite understand earlier.

François Mauger wrote:

>> In fact, since we are only rendering the
>> characters "[-+e.0-9]" we could use a modified BCD or other compressed
>> format to provide the compression that is typically what people assume
>> in binary formats.
> 
> ok this is only a set of 14 glyphs so it could be hosted via short ints
> (with 2 bits unused) 

? I think each of 14 glyphs could be represented in 4 bits, with 2 bit 
patterns left over.

> consider a typical float (relative precision ~1e-7).
> If one need to store pi as +0.3141592e+01 (ASCII) it is 14 characters
> (only 11 is one saves leading'+' and exponent '+0' chars for >0 mantissa
> and exponent)
> that could be serialized using 14/11 shorts, so this is 28/22 bytes.
> This has to be compared with 4 bytes for floats! 

It seems to me that 14 characters in the constrained glyph set could be 
represented with 14 4-bit "nybbles," or 7 bytes.

It's still worse than 4 bytes, but by a factor < 2 rather than ~6.

Please forgive me if I've misunderstood you.