Motorola DSP96002 - Manual (Page 564)

MOTOROLA DSP96002 USER’S MANUAL B-45
indspc equ 5.0 ;index spacing
rindspc equ 1.0/indspc ;reciprocal of index spacing
move #table,n0 ;point to start of table
move #firstindex,d6.s ;value of first index
move #rindspc,d7.s ;reciprocal of index spacing
fsub.s d6,d0 ;adjust input relative to index 1 1
fmpy.s d7,d0,d0 ;reduce range and create index 1 1
floor d0,d1 ;get index 1 1
int d1 d1.s,d2.s ;convert index to int,copy int part 1 1
fsub.s d2,d0 d1.l,r0 ;x-X(i), get ptr to table 1 1
nop ;clear address ALU pipe 1 1
move (r0)+n0 ;point to Y(i) 1 1
move x:(r0)+,d4.s ;get Y(i) 1 1
move x:(r0),d5.s ;get Y(i+1) 1 1
fsub.s d4,d5 ;Y(i+1)-Y(i) 1 1
fmpy.s d0,d5,d5 ; *(x-X(i)) 1 1
fadd.s d5,d4 ;+Y(i) 1 1
--- ---
Totals: 12 12
B.1.25 Argument Reduction
Argument reduction (AR) is the problem of having a desired floating point number range and an argument
that is outside of the range. The argument is placed inside of the desired range by adding or subtracting
multiples of the desired number range. Of course, adding and subtracting multiples of a number is inher-
ently slow and requires infinite precision. Some simple methods can be used with some assumptions on
the precision of the data and relative argument sizes.
The following program performs AR when the desired range is arbitrary and the input value is arbitrary. This
may be used to reduce an angle to the range of -pi to pi.
The following variables are defined:
rmin = range minimum value, -pi in this example
rmax = range maximum value, pi in this example
range = rmax-rmin, 2*pi in this example
o_range = 1.0/range
Assume the input is in d0.