Hi all,
Probably I found bug in nodes cost in vector network analysis (tested in G7, probably it affects all branches). Problem is in lib/vector/Vlib/net.c:
int cost;
…
(* dglInt32_t)(dglInt32_t) & cost
int cost is cast into dglInt32_t pointer. DGLib dglInt32_t is long. I am relatively new to C so I do not understand the way it is casted and I can miss something. I am reading it as cast address of cost int to dglInt32_t and then to pointer to dglInt32_t. It does not make sense to me but it compiles 
The problem is when you have on your system different size of long and int, it is probably also the reason why it was not noticed so far (on 32 bit usually sizeof(int) == sizeof(long)). Because it seems that during this cast there are added bytes to be same size as long. However these bytes have random values and therefore results costs do not make sense.
If this change is made everything seems ok:
dglInt32_t dgl_cost;
…
dgl_cost = cost;
dglNodeSet_Attr(gr, dglGetNode(gr, (dglInt32_t) cat),
& dgl_cost);
Now there is:
dglNodeSet_Attr(gr, dglGetNode(gr, (dglInt32_t) cat),
(* dglInt32_t)(dglInt32_t) & cost);
I have attached also patch.
Best
Stepan
(attachments)
nodes_costs.diff (857 Bytes)
On Mon, Jun 10, 2013 at 10:29 PM, Štěpán Turek <stepan.turek@seznam.cz> wrote:
Hi all,
Probably I found bug in nodes cost in vector network analysis (tested in G7,
probably it affects all branches). Problem is in lib/vector/Vlib/net.c:
int cost;
...
(* dglInt32_t)(dglInt32_t) & cost
int cost is cast into dglInt32_t pointer. DGLib dglInt32_t is long. I am
relatively new to C so I do not understand the way it is casted and I can
miss something. I am reading it as cast address of cost int to dglInt32_t
and then to pointer to dglInt32_t. It does not make sense to me but it
compiles
The problem is when you have on your system different size of long and int,
it is probably also the reason why it was not noticed so far (on 32 bit
usually sizeof(int) == sizeof(long)). Because it seems that during this cast
there are added bytes to be same size as long. However these bytes have
random values and therefore results costs do not make sense.
I think the reason why this has not been noticed yet is that not many
users are working with node costs. 64 bit systems with sizeof(long) >
sizeof(int) are commonly used for quite a few years by now.
The type name dglInt32_t is confusing because it is not necessarily a
32bit integer, it is an integer with at least 32 bits.
If this change is made everything seems ok:
dglInt32_t dgl_cost;
...
dgl_cost = cost;
dglNodeSet_Attr(gr, dglGetNode(gr, (dglInt32_t) cat),
& dgl_cost);
Now there is:
dglNodeSet_Attr(gr, dglGetNode(gr, (dglInt32_t) cat),
(* dglInt32_t)(dglInt32_t) & cost);
I have attached also patch.
Makes sense. I have applied the patch to all branches in r56680-2.
Markus M