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Language Assembler (68K)
| Date: | 06/29/05 |
| Author: | Alex Peters |
| URL: | n/a |
| Comments: | 0 |
| Info: | http://www.pilotwarez.com/index.php?page=asmbasics |
| Score: |  (3.20 in 44 votes) |
*
* Motorola 68000 assembly code to '99 Bottles of Beer'
* Written by Alex Peters, 29/6/2005
*
org $1000 code space
move.l #$7ffe,sp initialise stack pointer
move.b #99,d1 initialise beer count
main_loop bsr print_b print 'xx bottles of beer'
lea s_l1a,a1
bsr print_s print ' on the wall, '
bsr print_b print 'xx bottles of beer'
lea s_l1b,a1
bsr print_s print full stop, new line
lea s_l2a,a1
bsr print_s print 'Take one down, pass it around,'
sub.b #1,d1 decrement beer count
bsr print_b print 'xx bottles of beer'
lea s_l2b,a1
bsr print_s print ' on the wall.' and new line
cmp.b #0,d1
bne main_loop repeat while there are beers
lea s_final,a1
bsr print_s print final verse
move.b #TO_OS,d7
trap #14 return to OS
* The print_b subroutine prints 'xx bottles of beer' to the screen where xx
* is read from register d1.
print_b move.b #OUTCH,d7 prepare to display characters
cmp.b #0,d1
beq print_b_none print 'no more' if zero
clr.l d2
move.b d1,d2 copy beer count
divu #10,d2 and split into two digits
beq print_b_unit branch if no tens digit
move.b d2,d0
add.b #$30,d0 convert number to ASCII
trap #14 display tens digit
print_b_unit lsr.l #8,d2 shift other digit over
lsr.l #8,d2
move.b d2,d0
add.b #$30,d0 convert number to ASCII
trap #14 display units digit
bra print_b_bott
print_b_none lea s_nomore,a1
bsr print_s print 'no more' for zero
print_b_bott lea s_bottle,a1
bsr print_s print ' bottle'
cmp.b #1,d1 if beer count is not 1
beq print_b_of then don't print 's'
move.b #'s',d0
trap #14 otherwise do
print_b_of lea s_ofbeer,a1
bsr print_s print ' of beer'
rts return to caller
* The print_s subroutine prints a null-terminated string starting from a1.
print_s move.b #OUTCH,d7 prepare to display characters
move.l a1,a2 initialise memory pointer
print_s_loop move.b (a2)+,d0 read next character
beq print_s_done branch if it's a null
trap #14 otherwise display it
bra print_s_loop
print_s_done rts return to caller
* String and constant declarations follow.
s_nomore dc.b 'no more',NULL
s_bottle dc.b ' bottle',NULL
s_ofbeer dc.b ' of beer',NULL
s_l1a dc.b ' on the wall, ',NULL
s_l1b dc.b '.',CR,LF,NULL
s_l2a dc.b 'Take one down, pass it around, ',NULL
s_l2b dc.b ' on the wall.',CR,LF,CR,LF,NULL
s_final dc.b 'No more bottles of beer on the wall, '
dc.b 'no more bottles of beer.',CR,LF
dc.b 'Go to the store and buy some more... '
dc.b '99 bottles of beer!',CR,LF,NULL
NULL equ 0
LF equ 10
CR equ 13
TO_OS equ 228
OUTCH equ 248
end
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