Re: Byte ordering

[Z F <mail4me9999 at yahoo dot com>]

Hello,

Thank you Pedro for your reply, but I realized I was not clear.
double is an 8-byte quantity (at least on intel) so I need
64-bit-swapping routines not 32-bit ones which are available.
Also, htonl() and ntohl() are for ints. I could cast double to int but
this would require splitting the double into two parts mantissa and
exponent and applying 32-bit swaps independently. Is this the way to
go?

Need more input :-)

Lazar

--- Pedro Gonnet <pedro@vis.ethz.ch> wrote:
> 
> Hello Lazar,
> 
> I think the functions you're looking for are 
> 
> 	uint32_t htonl(uint32_t hostlong);
> 	uint32_t ntohl(uint32_t netlong);
> 
> These operate on 32-bit values, so you have to do something like
> 
> 	double hton_double ( double in ) {
> 
> 	   double res;
> 	   unsigned int *in , *out = (unsigned int *)(&res);
> 
> 	   out[0] = htonl(in[0]);
> 	   out[1] = htonl(in[1]);
> 
> 	   return res;
> 
> 	   }
> 
> Beware that on some machines (or with data dumped by programs
> compiled
> with Portland's byte-swapping fortran compiler), the 32-bit values
> are
> also swapped, in which case you would have to write:
> 
> 	out[0] = htonl(in[1]);
> 	out[1] = htonl(in[0]);
> 
> Hope this helps...
> 
> Pedro
> 
> 
> 
> 
> On Tue, 2003-09-30 at 16:41, Z F wrote:
> > Hello everybody,
> > 
> > 
> > Even though this question is not directly related to GSL,
> indirectly
> > --- it is.
> > 
> > I have a scientific calculation program (which uses GSL) but most
> > importantly it uses doubles. I need to transfer those data to
> another
> > computer. The problem is that if the two computers have different
> byte
> > ordering, I have to do something special about the data. I
> understand
> > that there is a network standard for shorts and for ints to serve
> this
> > purpose. I could not find any standards to transfer doubles/floats
> over
> > net. I the past I could live with printf()-type things and convert
> all
> > doubles to strings and pass strings since ASCII is more universal.
> > This, however, increases the data size by a factor of three.
> > 
> > The current problem I am working on has data output rate of about
> > 5-15MBytes/sec and increasing it by factor of three is not
> feasible.
> > 
> > Could someone, please, point me in the right direction? Should I
> > give-up  on portability of my code and assume/hope that both ends
> use
> > the same 
> > byte ordering?
> > 
> > I know that this is not directly related to GSL, but all the
> network
> > people do not seem to care about doubles so I have to turn to
> > "scientific" network programming....
> > 
> > Thank you very much for your input,
> > 
> > Lazar
> > 
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