Assign linear interpolation between two other float arrays. We take ACount items, from V1[Index1 ... Index1 + ACount - 1] and V2[Index2 ... Index2 + ACount - 1], and interpolate between them like normal Lerp functions.
It's Ok for both V1 and V2 to be the same objects. But their ranges should not overlap, for future optimizations (although it's Ok for current implementation).