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rotate90.asm
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.data 0x10008000
vetor: .word 1 2 3 4 5 6 7 8 9
.text
li $a0, 3
la $a1, 0x10008000
jal rotate90l
li $v0, 10
syscall
#for an nxm matrix where n=m
#https://en.wikipedia.org/wiki/In-place_matrix_transposition
#for n = 0 to N - 2
# for m = n + 1 to N - 1
# swap A(n,m) with A(m,n)
rotate90l:
# Register usage:
# a0: image height or width in pixels(since they are equal doesnt matter)
# a1: start address of the image
#
# t0: line iterative index (n)
# t1: number of matrix lines (N)
# t2: stop condition of the upper for (forNminus2)
# t3: column iterative index (m)
# t4: stop condidition of the lower for (forNminus1)
# t5: byte A(n,m) address
# t6: byte A(m,n) address
# t7: line break address amount
# t8: start address for iterating A(n,n)
# t9: stack for saving registers before swapTerms call
# 0($t9): t0
# 4($t9): t1
# 8($t9): t2
# 12($t9): t3
# 16($t9): t4
# 20($t9): t5
# 24($t9): t6
# 28($t9): t7
# 32($t9): t8
# 36($t9): ra (return address)
#for n = 0 to N - 2
# for m = n + 1 to N - 1
# swap A(n,m) with A(m,n)
li $t0, 0 #t0 will be n
add $t1, $a0, $zero #t1 will be N
add $t1, $t1, 1 #Will correct the zero-indexing of the matrix address
add $t2, $t1, -2 #t2 will be the stop conditon of forNminus2
mul $t7, $a0, 4 #t7 will be \n address amount
add $t8, $a1, $zero #t8 will be the A(n,n) adress
forNminus2:
beq $t0, $t2, end_forNminus2
add $t3, $t0, 1 #t3 will be m
add $t4, $t1, -1 #t4 will be the stop condition of forNminus1
add $t5, $t8, $zero #refresh the address of A(n,m)
add $t6, $t8, $zero #refresh the address of A(m,n)
forNminus1:
beq $t3, $t4, end_forNminus1
add $t5, $t5, 4
add $t6, $t6, $t7
#registerSave:
add $sp, $sp, -40
add $t9, $sp, $zero
sw $t0, 0($t9)
sw $t1, 4($t9)
sw $t2, 8($t9)
sw $t3, 12($t9)
sw $t4, 16($t9)
sw $t5, 20($t9)
sw $t6, 24($t9)
sw $t7, 28($t9)
sw $t8, 32($t9)
sw $ra, 36($t9)
#end registerSave
add $a0, $t5, $zero
add $a1, $t6, $zero
jal swapTerms
#registerRecovery:
lw $t0, 0($t9)
lw $t1, 4($t9)
lw $t2, 8($t9)
lw $t3, 12($t9)
lw $t4, 16($t9)
lw $t5, 20($t9)
lw $t6, 24($t9)
lw $t7, 28($t9)
lw $t8, 32($t9)
lw $ra, 36($t9)
add $sp, $sp, 40
#end registerRecovery
add $t3, $t3, 1
j forNminus1
end_forNminus1:
#end
add $t8, $t8, $t7
add $t8, $t8, 4
add $t0, $t0, 1
j forNminus2
end_forNminus2:
#end
jr $ra
#end rotate90l
swapTerms:
# Register usage:
# a0: address of the first term
# a1: address of the second term
lw $t0, 0($a0)
lw $t1, 0($a1)
sw $t1, 0($a0)
sw $t0, 0($a1)
jr $ra
#end swapTerms