/** Calculate single differences from two sets of observations.
* Undifferenced input observations are assumed to be both taken at the
* same time, `t`.
*
* SNR in the output is the lesser of the SNRs of inputs a and b.
*
* `sat_pos` and `sat_vel` are taken from input b.
*
* \param n_a Number of measurements in set `m_a`
* \param m_a Array of undifferenced observations, as a set sorted by PRN
* \param n_b Number of measurements in set `m_b`
* \param m_b Array of undifferenced observations, as a set sorted by PRN
* \param sds Single difference observations
*
* \return The number of observations written to `sds` on success,
* -1 if `m_a` is not a valid set,
* -2 if `m_b` is not a valid set
*/
u8 single_diff(u8 n_a, navigation_measurement_t *m_a,
u8 n_b, navigation_measurement_t *m_b,
sdiff_t *sds)
{
return intersection_map(n_a, sizeof(navigation_measurement_t), m_a,
n_b, sizeof(navigation_measurement_t), m_b,
nav_meas_cmp, sds, single_diff_);
}
/** Take the intersection of two sets.
*
* Takes two arrays each representing a set and outputs two arrays containing
* the elemnts from the input arrays that are equal under a comparison function
* `cmp`.
*
* Set A and B should be represented as sorted arrays with no repeated
* elements.
*
* \param na Number of elements in set A
* \param sa Size of each element of set A
* \param as Array of elements in set A
* \param a_out Output array of matching elements from A
* \param nb Number of elements in set B
* \param sb Size of each element of set B
* \param bs Array of elements in set B
* \param b_out Output array of matching elements from B
* \param cmp Pointer to a comparison function
*
* \return Number of elements in intersection on success,
* -1 if A is not a valid set,
* -2 if B is not a valid set
*/
s32 intersection(u32 na, size_t sa, const void *as, void *a_out,
u32 nb, size_t sb, const void *bs, void *b_out,
cmp_fn cmp)
{
struct intersection_context ctxt = {
.a_out = a_out,
.sa = sa,
.b_out = b_out,
.sb = sb
};
return intersection_map(na, sa, as, nb, sb, bs,
cmp, &ctxt, intersection_function);
}
