Vectors & Matrices

Endianness

The MIPS architecture allows both big-endian and little-endian byte ordering, but the little-endian one is most commonly used. Endianness has to do on how bytes are addressed in memory, and it's related to how the access of each individual byte is made.

ASCII

TODO ASCII

Vectors

There are many types of vectors you can handle in MIPS:

.data
    byte: .byte 29, 8, 1, 29, 2, -3
    half: .half 10, -4, 20, -8, 22, 12
    word: .word 2, 29012, 29, 5, -12905, -290125

    # decimal 

    float: .float 2.5, -1.2, 21.90, -5.0
    double: .double 2.5, -1.2, 21.90, -5.0

    # strings

    string: .asciiz "Holy Moly, who ate my Canoli?"

Note that .asciiz stands for "zero terminated string", which means it has a '\0' nullchar at the end.

Vector Iterations

You can iterate vectors and matrices in two ways:

Index

useful if you need the index of each element
the increment of the index doesn't depend on the size of the elements
you have to convert the index each time, according to the size of the elements

.data
    vector: .word 10, 2, 980, 29, 1992, -2, 59, 280, 99
    size: .word 9
.text
    la $s0, vector #; s0 = vector address
    la $t1, size #; t1 = address of size
    lw $t1, ($t1) #; t1 = size

    li $t0, 0 #; t0 is the index i

    for:
        bge $t0, $t1, end #; if i == size, end loop

        sll $t2, $t0, 2 #; offset = i * 4 (shift logic left by 2)
        addi $t2, $t2, $s0 #; t2 = current address = offset + address

        lw $t7, ($t2) #; load value from current address, and maybe use it

        #; rest of the code ...

        addi $t0, $t0, 1 #; i = i + 1
        j for #; loop again
    end:

TODO: check if it works

Pointer

you work directly with the address
less calculations to do in the cycle
you don't have the index of the element
the increment depends on the size of the elements
you must calculate the index after the last element

.data
    vector: .word 10, 2, 980, 29, 1992, -2, 59, 280, 99
    size: .word 9
.text
    la $t0, vector #; t0 = vector address

    la $t1, size #; t1 = address of size
    lw $t1, ($t1) #; t1 = size
    sll $t1, $t1, 2 #; size = size * 4 (we are handling words)
    add $t1, $t0, $t1 #; t1 = end address = vector address + size * 4 (this is the address after the last one in the vector)

    for:
        bge $t0, $t1, end #; if current address == vector end address, end loop

        lw $t7, ($t0) #; load value from current address, and maybe use it

        #; rest of the code ...

        addi $t0, $t0, 4 #; current address = current address + 4 (we move by 4 bytes, because we are using words) 
        j for #; loop again
    end:

TODO: check if it works

Matrices

If you want a 7 (rows) x 13 (columns) matrix, you need enough space for 91 elements:

.data
    matrix: .word 0:91

Matrixes are stored in memory like vectors, each row is laid one after the other. To work with n-sized matrices, you just lay out one matrix after the other in memory (you can have a 3-dimensional matrix, for example, where the z coordinate dictates the layer, or the matrix, you are working with)

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