Lab 8 Carleton University SYSC 3006

Fragment 1:


B Main

ExampleString ; start of packed string

DCD #0x53595343 ; ‘S’=0x53 ‘Y’=0x59 ‘S’=0x53 ‘C’=0x43

DCD #0x20333030

DCD #0x36210000 ; 1st 00 is the null-terminator, 2nd 00 is just padding to fill the word

Main

; R0 = address of the packed string




m
er as
LEA R0, [ ExampleString ]




co
eH w
; R1 = index of the character in the packed string ... test with several values




o.
MOV R1, #5

rs e
; the following code puts the indexed character into the least significant byte of R0,
ou urc
; and clears the remainder of R0
o

; ---- start of block to copy into Fragment 2 ----
aC s


; R2 = offset to word containing indexed character
vi y re



LSR R2, R1, #2 ; divide index by 4

; R3 = word containing indexed character
ed d




LDR R3, [ R0, R2 ]
ar stu




; R1 = digit offset of indexed character in R3 (digit offset = 0, 1, 2 or 3)

AND R1, R1, #3
sh is




; need to shift character from current position to least significant byte
Th




; need to shift 8 bits for each digit position

; R1 = number of digit shifts needed

MOV R4, #3

SUB R1, R4, R1

BEQ DoneShiftLoop ; if 0 shifts needed, then done shifting

; shift character into least significant byte

ShiftLoop



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https://www.coursehero.com/file/24395275/Lab-8pdf/

, LSR R3, R3, #8

SUB R1, R1, #1

BNE ShiftLoop

DoneShiftLoop

; R3 now has indexed character in least significant byte,

; but may have additional characters in higher bits

; R0 = indexed character with higher bits cleared

AND R0, R3, #0xFF

; ---- end of block to copy into Fragment 2 ----




m
er as
DCD #0xFFFFFFFF ; stop




co
=============================================




eH w
o.
Fragment 2:
rs e
ou urc
MOV R13, #0x800 ; initialize stack pointer

B Main
o

ExampleString ; start of packed string
aC s
vi y re


DCD #0x53595343 ; ‘S’=0x53 ‘Y’=0x59 ‘S’=0x53 ‘C’=0x43

DCD #0x20333030
ed d




DCD #0x36210000 ; 1st 00 is the null-terminator, 2nd 00 is just padding to fill the word
ar stu




; char CharAt ( &( PackedString[] ), uint charIndex )
sh is




; accepts R0 = address of PackedString[] (by reference),
Th




; R1 = charIndex (by value)

; returns R0 = PackedString[ charIndex ]


CharAt

PUSH {R1,R2,R3,R4,R14} ; save registers (SYSC 3006 Register Preservation convention)


; ---- start of block copied from Fragment 1 ----




This study source was downloaded by 100000850872992 from CourseHero.com on 03-24-2023 01:11:09 GMT -05:00
https://www.coursehero.com/file/14306242/lab8syscpdf/


https://www.coursehero.com/file/24395275/Lab-8pdf/