HexLoc MachWord Label Source Code Comments
00000000 00000000
.org 1000H
00001000 80000000 A:
.dc 80000000H ;Most negative 32 bit number
00001004 ffffffff B:
.dc -1
;Minus 1
00001008 00000000 SUM:
.dw 1
;Make room for sum
0000100c 00000000 Overflow:
.dc 0
;No Overflow
00001010 00000000
.org 5000H
00005000 2a80503c
la r10, Finish ;Finished routine
00005004 2ac05030
la r11, Minus ;A is negative
00005008 2901ffff
la r4, -1 ;Used if overflow
occurs
0000500c 107fbff0
ldr r1, A ;Put A in
r1
00005010 10bfbff0
ldr r2, B ;Put B in
r2
00005014 60c22000
add r3, r1, r2 ;Sum goes to r3
00005018 20ffbfec
str r3, SUM ;Store SUM
0000501c 40161005
brmi r11, r1 ;A is negative
00005020 40142005
brmi r10, r2 ;B is negative -- No Overflow
00005024 40143004
brpl r10, r3 ;Sum is also positive --
;No overflow
00005028 213fbfe0
str r4, Overflow ;Set Overflow indicator
0000502c 40140001
br r10
;Finished with
;positive numbers
00005030 40142004 Minus:
brpl r10, r2 ;B is plus -- No overflow
00005034 40143005
brmi r10, r3 ;Sum is also negative --
;no overflow
00005038 213fbfd0
str r4, Overflow ;Set Overflow indicator
0000503c f8000000 Finish:
stop
This program repeats the action taken to indicate overflow for both negative and positive numbers. It gives greatest flexibility in cases where different actions must be taken for positive and negative numbers -- for example if the overflow indicator were set at +1 for positive numbers and -1 for negative numbers. Contrast this with the program shown after the picture of the simulator window.
HexLoc
MachWord Label
Source Code
Comments
00000000 00000000
.org 1000H
00001000 80000000 A:
.dc 80000000H ;Most negative 32 bit
;number
00001004 ffffffff B:
.dc -1
;Minus 1
00001008 00000000 SUM:
.dw 1
0000100c 00000000 Indicator:
.dc 0
00001010 00000000
.org 5000H
00005000 2a80503c
la r10, Finish ;Finished routine
00005004 2ac05030
la r11, Minus ;A is negative
00005008 2b005038
la r12, Overflow ;Address of overflow routine
0000500c 2901ffff
la r4, -1 ;Used
if overflow occurs
00005010 107fbfec
ldr r1, A
00005014 10bfbfec
ldr r2, B
00005018 60c22000
add r3, r1, r2
0000501c 20ffbfe8
str r3, SUM ;Store SUM
00005020 40161005
brmi r11, r1 ;A is negative
00005024 40142005
brmi r10, r2 ;B is negative --
;No Overflow
00005028 40183005
brmi r12, r3 ;Sum is also negative
--
;Overflow
0000502c 40140001
br r10
;Finished with positive
;numbers
00005030 40142004 Minus:
brpl r10, r2 ;B is plus --
;No overflow
00005034 40143005
brmi r10, r3 ;Sum is also negative
--
;no overflow
00005038 213fbfd0 Overflow:
str r4, Indicator ;Set overflow indicator
0000503c f8000000 Finish:
stop
This program uses a single routine
to indicate overflow for both positive and negative numbers and
is more efficient when the overflow routine is long. In
this case both programs are equally efficient and require 16 instructions
plus assembler directives.