Motorola DSP96002 - Manual (Page 563)

B-44 DSP96002 USER’S MANUAL MOTOROLA
B.1.24 Table Lookup with Linear Interpolation Between Points
This performs a table lookup and linear interpolation between points in the table. It is assumed that the
spacing between the known values (breakpoints) is a constant. No range checking is performed on the
input number because it is assumed that previous calculations may have limiting and range checking. This
can be used to approximate arbitrary functions given a set of known points (such as digital sine wave gen-
eration) or to interpolate linearly between values of a set of data such as an image.
The function to be approximated is shown below:
o ¨ known values of function
o o
Y(i) o
o
----+------+------+------+------+
X(i)
→
1.0 6.0 11.0 16.0 21.0 ¨ indexes
^ / spacing between indexes is INDSPC, 5.0
in this example
FIRSTINDEX - value of the first index in the table, 1.0
in this example
Given an input value "x", the linearly interpolated value "y" from the tabulated known values is:
Y(i+1)-Y(i)
y = --------------(x-X(i)) + Y(i)
X(i+1)-X(i)
Program ICycles
Words
;
; Approximate d4=exp(d0) for 1.0 <= x <= 21.0
;
page 132,60,1,1
org x:0
table dc 2.7182818e+00 ;exp(1.0)
dc 4.0342879e+02 ;exp(6.0)
dc 5.9874141e+04 ;exp(11.0)
dc 8.8861105e+06 ;exp(16.0)
dc 1.3188157e+09 ;exp(21.0)
org p:$50
firstindex equ 1.0 ;value of first table index