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Motorola DSP96002 User Manual

Page 573

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B-54

DSP96002 USER’S MANUAL

MOTOROLA

9. Dynamic bit field clear. Register d1.l contains FOFF, d2.l contains

FSIZE.

Program

ICycles

Words

move #32,d3.l ;register size 1 1 sub

d2,d3 #-1,d2.l ;32-fsize, get 1s mask 2 2 move

d3.l,d3.h ;move shift count 1 1 lsr d3,d2 d1.l,d1.h

;trim mask, get foff 1 1 lsl d1,d2 ;align

mask 1 1 andc d2,d0 ;invert mask

and clear 1 1

--- ---

Totals: 7 7

10. Dynamic bit field set. Register d1.l contains FOFF, d2.l contains FSIZE.

Program

ICycles

Words

move #32,d3.l ;register size 1 1 sub

d2,d3 #-1,d2.l ;32-fsize, get 1s mask 2 2 move

d3.l,d3.h ;move shift count 1 1 lsr d3,d2 d1.l,d1.h

;trim mask, get foff 1 1 lsl d1,d2 ;align

mask 1 1 or d2,d0 ;clear bit

field 1 1

--- ---

Totals: 7 7

B.1.29 Newton-Raphson Approximation for 1.0/SQRT(x)

The Newton-Raphson iteration can be used to approximate the function:

1.0

y= -------
sqrt(x)

by minimizing the function:

1.0

F(y) = x - -------
y*y

Given an initial approximate value y=1/sqrt(x), the Newton-Raphson iteration for refining the estimate is:

y(n+1)=y(n)*(3.0-x*y*y)/2.0

Newton-Raphson Approximation

Program

ICycles

of 1.0/SQRT(x)

Words