Embedded Software and Motor Control Libraries for PXR40xx

Function GFLIB_Lut1D_F16
Table 4-87. GFLIB_Lut1D example table (continued)
0.5 N/A 2*(2 -1 )
The Table 4-87 contains 4 interpolating points (note four rows). The interpolating
interval length in this example is equal to 2 -1 . The pf16Table parameter points to the
second row, defining also the interpolating index 0. The x-coordinates of the interpolating
points are calculated in the right column.
It should be noted that the pf16Table pointer does not have to point to the start of the
memory area of ordinate values. Therefore, the interpolating index can be positive or
negative or, even, does not have to have zero in its range.
A special algorithm is used to make the computation efficient, however, under some
additional assumptions, as provided below:
• the values of the interpolated function are 16 bits long
• the length of each interpolating interval is equal to 2 -n , where n is an integer in the
range of 1, 2, ... 13
• the provided abscissa for interpolation is 16 bits long
The algorithm performs the following steps:
1. Compute the index representing the interval, in which the linear interpolation will be
performed:
Equation GFLIB_Lut1D_Eq2
where I is the interval index and the s Interval the shift amount provided in the
parameters structure as the member s16ShamIntvl. The operator >> represents the
binary arithmetic right shift.
2. Compute the abscissa offset within an interpolating interval:
3.
Equation GFLIB_Lut1D_Eq3
where Δ{x} is the abscissa offset within an interval and the s Offset is the shift amount
provided in the parameters structure. The operators