FreeTDS Development Group

["Thompson, Bill D (London)" <ThompBil AT exchange.uk.ml.com>]

james,

I guess what I was trying to say is this :

consider a money value of  1. 
This is represented by two 4 byte integers, each independently big or little
endian.

On bigendian they would be:

0 0 0 0     0 0 0 1

which, if you were to cast the data to an 8 byte integer would make sense.


On little endian the two bytes would be:

0 0 0 0    1 0 0 0

which, if you were to cast the data to an 8 byte integer would NOT make
sense (well it would , but the number would be wrong). The number 1 , on a
little endian machine in an 8 byte integer would presumably be:

1 0 0 0    0 0 0 0

HTH, How did you get on ?

Bill


> -----Original Message-----
> From: James K. Lowden [SMTP:jklowden AT schemamania.org]
> Sent: Thursday, August 08, 2002 1:59 AM
> To:   TDS Development Group
> Subject:      [freetds] RE: money wire format
> 
> On Wed, 7 Aug 2002 23:13:11 +0100, "Thompson, Bill D (London)"
> <ThompBil AT exchange.uk.ml.com> wrote:
> 
> > On a big endian machine the two 4 byte integers, strung together , can
> > be treated as a single entity.
> > On little endian of course they cannot. 
> 
> Of course?  I guess I don't understand what "strung together" means.  :) 
> We can do 64-bit integer math.  Does that count?  
> 
> > Assuming we dont change tds_process_row, 
> 
> But we probably should ...
> 
> > and the money value comes down
> > unchanged the bytes would have to be moved as follows ( I reckon, and it
> > IS late here )
> > 
> > Wire: 
> > 
> > 1 2 3 4   5 6 7 8
> > 
> > To:
> > 
> > 5 6 7 8   1 2 3 4 
> > 
> > does that make sense ?
> 
> Thanks, Bill.  It makes sense, except that I was expecting:
> 
> 8 7 6 5 4 3 2 1
> 
> (assuming each digit represents one byte).  That's what you get with:
> 
>       char buf[] = "12345678";
>       int i = tds_swap_bytes( buf, 8 );
>       printf( "%d bytes swapped: \"%s\"\n", i, buf );
> 
> I also experimented with ntohl and htonl, program below.  The output:
> 
> $ gcc -g  -o swaptest swaptest.c 
> $ ./swaptest 
> 8 bytes input:    "12345678"
> 8 bytes swapped:  "87654321"
> 8 bytes reverted: "12345678"
> 
> ntohl,  input: "1234"
> ntohl, output: "4321"
> htonl, output: "1234"
> 
> I wonder what "htonll" would do?  
> 
> I'll mangle a few and see how it goes.  
> 
> 
> 
> 
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