Arrays

Question 1

steps to access specific element in 1d array

Answer 1

1. byte offset = index * element size

2. address = base address + byte offset

Question 2

retrieve the 4th element (index = 3) off an array of word sized values stored in memory at the address in R4

Answer 2

LDR R5, =3

LDR R6, [R4, R5, LSL #2]

Question 3

Why use LSL #2 when working with word sized values

Answer 3

equivalent to multiplying register by 4

Question 4

how can 2D arrays be mapped in memory

Answer 4

each row in 2D array is mapped as sequential 1D arrays

Question 5

steps to access 2D array elements

Answer 5

1. index = (row * row size) + col
2. byte offset = index * element size
3. address = base address + offset

Question 6

retrieve the element from index [3][2] in an array of words with 6 rows and 8 columns
address starts at R4, no of rows in R5. no of cols in R6

Answer 6

LDR R1, =3
LDR R2, =2

MUL R7, R1, R6 @index = row by row size
ADD R7, R7, R2 @index += col
LDR R0, [R4, R7, LSL #2} @elem = word[array + (index*elemSize)}