Vector arguments of VML mathematical functions are passed in one-dimensional arrays with unit vector increment. It means that a vector of length n is passed contiguously in an array a whose values are defined as a[0], a[1], ..., a[n-1] (for the C interface).
To accommodate for arrays with other increments, or more complicated indexing, VML contains auxiliary pack/unpack functions that gather the array elements into a contiguous vector and then scatter them after the computation is complete.
Generally, if the vector elements are stored in a one-dimensional array a as a[m0], a[m1], ..., a[mn-1]
and need to be regrouped into an array y as y[k0], y[k1], ..., y[kn-1],
VML pack/unpack functions can use one of the following indexing methods:
kj = incy * j, mj = inca * j, j = 0 ,..., n-1
Constraint: incy > 0 and inca > 0.
For example, setting incy = 1 specifies gathering array elements into a contiguous vector.
This method is similar to that used in BLAS, with the exception that negative and zero increments are not permitted.
kj = iy[j], mj = ia[j], j = 0 ,..., n-1,
where ia and iy are arrays of length n that contain index vectors for the input and output arrays a and y, respectively.
Indices kj
, mj are such that: my[kj] ≠ 0, ma[mj] ≠ 0 , j = 0,..., n-1,
where ma and my are arrays that contain mask vectors for the input and output arrays a and y, respectively.
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