Advanced Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 167

; the following eight instructions subtract the divisor from register R
ldd R 1 2,sp
subd divisor 1 2,sp
std buf 1 2,sp
ldaa R 1 1,sp
sbca divisor 1 1,sp
staa buf 1 1,sp
ldaa R,sp
sbca divisor,sp
bcs smaller
; the following six instructions store the difference back to R register

staa R,sp

ldaa buf 1 1,sp

staa R 1 1,sp

ldd buf 1 2,sp

std R 1 2,sp

bset Q 1 3,sp,$01 ; set the least significant bit of Q register to 1

bra looptest

smaller bclr Q 1 3,sp,$01 ; set the least significant bit of Q register to 0

looptest dec i,sp
lbne loop
; the following four instructions copy the remainder into the hole in the stack
ldd R,sp
std rem,sp
ldd R 1 2,sp
std rem 1 2,sp
; the following four instructions copy the quotient into the hole in the stack

ldd Q,sp

std quo,sp

ldd Q 1 2,sp

std quo 1 2,sp

leas locVar,sp ; deallocate local variables

puly

pulx

puld

rts

; org $FFFE ; uncomment this line for CodeWarrior

; dc.w start ; uncomment this line for CodeWarrior

end

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4.7.2 Finding the Square Root
There are several methods available for finding the square root of a number q . One of the
methods is based on successive approximation shown in Figure 4.12. The square root of a 2 n -
bit number is n bits long. The successive approximation method computes the square root of a
32-bit integer in the following manner:
Step 1
sar ← 0; mask ← $8000; lpcnt ← 16; temp ← 0