.globl read_matrix

.text
# ==============================================================================
# FUNCTION: Allocates memory and reads in a binary file as a matrix of integers
#   If any file operation fails or doesn't read the proper number of bytes,
#   exit the program with exit code 1.
# FILE FORMAT:
#   The first 8 bytes are two 4 byte ints representing the # of rows and columns
#   in the matrix. Every 4 bytes afterwards is an element of the matrix in
#   row-major order.
# Arguments:
#   a0 is the pointer to string representing the filename
#   a1 is a pointer to an integer, we will set it to the number of rows
#   a2 is a pointer to an integer, we will set it to the number of columns
# Returns:
#   a0 is the pointer to the matrix in memory
# ==============================================================================
read_matrix:

    # Prologue
    addi sp, sp, -36
    sw ra, 0(sp)
    sw s0, 4(sp)
    sw s1, 8(sp)
    sw s2, 12(sp)
    sw s3, 16(sp)
    sw s4, 20(sp)
    sw s5, 24(sp)
    sw s6, 28(sp)
    sw s7, 32(sp)

    mv s0, a0 # preserve arguments
    mv s1, a1
    mv s2, a2

    li t1, 4 # size of bytes
    mv a1, a0 # move file name into a1
    li a2, 0 # read permissions
    jal ra fopen # open file
    addi t0, x0, -1
    beq x0 a0 eof_or_error # check error file
    mv t0, a0 # t0 is now file descriptor
    # read rows
    mv a1, t0
    mv a2, s1
    mv a3, t1 # 4 bytes
    mv s6, a3 # save this variable
    jal ra fread
    bne a0, s6, eof_or_error
    lw s3, 0(a2) # load num of rows
    # read columns
    mv a1, t0
    mv a2, s2
    mv a3, t1 # 4 bytes
    mv s6, a3 # save this variable
    jal ra fread
    bne a0, s6, eof_or_error
    lw s4, 0(a2) # load num of columns
    # mutiply and malloc space
    mul s5, s3, s4 # number of entries
    mul s5, s5, t1 # mul by byte size
    mv a0, s5  # malloc s5 amount of memory
    jal ra malloc # returns mallocd pointer to matrix in a0

    # read rest of matrix
    mv a1, t0 # file descriptor
    mv a2, a0 # mallocd memory
    mv a3, s5 # size

    mv s6, a3 # save byte length
    mv s7, a0 # save memory pointer
    jal ra fread
    bne a0, s6, eof_or_error

    # close file
    mv a1, t0
    jal ra fclose
    bne a0, x0, eof_or_error
    mv a0, s7 # move pointer to a0
    mv a1, s3 # num rows
    mv a2, s4 # num columns

    # Epilogue
    lw ra, 0(sp)
    lw s0, 4(sp)
    lw s1, 8(sp)
    lw s2, 12(sp)
    lw s3, 16(sp)
    lw s4, 20(sp)
    lw s5, 24(sp)
    lw s6, 28(sp)
    lw s7, 32(sp)
    addi sp, sp, 36
    ret

eof_or_error:
    li a1 1
    jal exit2