Motorola DSP96002 - Manual (Page 634)

MOTOROLA DSP96002 USER’S MANUAL B-115
B.1.46 Evaluation of LOG(x)
Floating-point evaluation of log
2
(x) can be performed by representing x as s*(2**e) where s is the signifi-
cand and e is the unbiased exponent. Then, log
2
(s*(2**e)) = log
2
(s) + e. After extracting the significand s,
log
2
(s) can be evaluated with a polynomial. By adding the unbiased exponent, log
2
(x) results. Various
execution speeds and accuracies may be determined by using different order polynomials.
page 132,60,1,1
org x:0
polyc
dc 0.6681523e-02 ;**8
dc -0.6736254e-01 ;**7
dc 0.2584541e+00 ;**6
dc -0.3676691e+00 ;**5
dc -0.4461204e+00 ;**4
dc 0.2740512e+01 ;**3
dc -0.5236615e+01 ;**2
dc 0.6184454e+01 ;**1
dc -0.3072334e+01 ;**0
org p:$100
;
; calculate d2=log2(d0)
;
Program ICycles
Words
getexp d0,d7 #polyc,r0 2 2
fgetman d0,d0 1 1
fclr d2 x:(r0)+,d1.s 1 1
do #9,_log2sig 2 3
fmpy.x d2,d0,d2 1 1
fadd.x d1,d2 x:(r0)+,d1.s 1 1
_log2sig
float.x d7 1 1
fadd.s d7,d2 1 1
--- ---
Totals: 10 27