E.1.12. - Getting and setting auxiliary data arrays
The user function overhead modules also provide you with a method
of storing auxiliary data arrays that have the same number of elements
as there are data points.
This auxiliary data is also kept in a temporary
file if there is not enough room in program memory.
The following functions handle the file control.
| Name |
What it Does |
 |
|
|
fpt_init(ptr, size) |
ptr points to static storage of size bytes |
fpt_get(i) |
Fetch the ith element |
fpt_set(i) |
Set the ith element |
fpt_fini() |
Bring the temporary file up to date |
|
The function
fpt_init() is used to initialize the auxiliary
storage routine.
You supply it with a pointer to the data structure
you are using and tell it how big that structure is.
The
fpt_get() and
fpt_set() routines then use that storage you have allocated
to transfer the data in and out.
For example,
{
Point pt;
static struct aux {
float a_1;
float a_2;
float a_3;
} aux;
static once;
...
if (!once) {
/* Initialize storage just once */
fpt_init(&aux, sizeof(aux));
once++;
}
for (i = 0; i get_npts(); i++) {
pt_get(&pt, i);
aux.a_1 = get_x(&pt);
aux.a_2 = get_x(&pt) * 2;
aux.a_3 = get_x(&pt) * 3;
fpt_set(i);
}
fpt_fini();
...
}
fpt_init() can be called more than once to reinitialize the
storage, perhaps using a different data structure.
Every time it is
called, though, the previously stored numbers are wiped out.
Call
it just once and the values stored will be retained over successive
invocations of the user function when it is reinvoked with the
fn .
syntax.
|
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