Embedded Software and Motor Control Libraries for PXR40xx

4.67.4 Description
where:
Equation GFLIB_Lut1D_Eq1
• y is the interpolated value
• y 1 and y 2 are the ordinate values at, respectively, the beginning and the end of the
interpolating interval
• x 1 and x 2 are the abscissa values at, respectively, the beginning and the end of the
interpolating interval
• the x is the input value provided to the function in the f32In argument
The interpolating intervals are defined in the table provided by the pf32Table member of
the parameters structure. The table contains ordinate values consecutively over the entire
interpolating range. The abscissa values are assumed to be defined implicitly by a single
interpolating interval length and a table index, while the interpolating index zero is the
table element pointed to by the pf32Table parameter. The abscissa value is equal to the
multiplication of the interpolating index and the interpolating interval length. For
example, let's consider the following interpolating table:
Table 4-85. GFLIB_Lut1D example table
ordinate (y) interpolating index abscissa (x)
-0.5 -1 -1*(2 -1 )
pf32Table 0.0 0 0*(2 -1 )
0.25 1 1*(2 -1 )
0.5 N/A 2*(2 -1 )
Chapter 4 API References
The Table 4-85 contains 4 interpolating points (note four rows). The interpolating
interval length in this example is equal to 2 -1 . The pf32Table 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 pf32Table 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:
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Freescale Semiconductor, Inc. 357