MIPS: Store integer data into array from file

Question

I am writing this code for a problem where I have to read integers from file and store them into an array to perform other operations. So far I have been able to read from file and store them into the buffer.

#### Read Data from File
li $v0, 14              # system call for read from file
move $a0, $s6     
la $a1, buffer          # address of buffer from which to read
li $a2, 1000            # hardcoded buffer length
syscall                 # read from file

When I do this: it sucessfuly displays the content of the file which are integers on separate lines.

li $v0, 4           # syscall for printing a string
la $a0, buffer          # load read data in $a0
syscall

I am stuck at this point where I have to store these integers in the buffer into an array. How is this done?

Answer 1

You didn't give us a lot of information to go on so I will be assuming your file looks something like this:

1234 523 54326 7131

(It can be line-delimited, the concept is the same)

Once you read the number into a string, you have to parse it into an integer. And then store it in an integer array. Your array should look something like this:

        .align 2    # word-aligned
array:  .space 40    # a word array of 10 elements

To parse the string to an integer you can barrow the concept from C, which has atoi() which looks something like this:

#
#  int atoi ( const char *str );
#
#  Parse the cstring str into an integral value
#
atoi:
    or      $v0, $zero, $zero   # num = 0
    or      $t1, $zero, $zero   # isNegative = false
    lb      $t0, 0($a0)
    bne     $t0, '+', .isp      # consume a positive symbol
    addi    $a0, $a0, 1
.isp:
    lb      $t0, 0($a0)
    bne     $t0, '-', .num
    addi    $t1, $zero, 1       # isNegative = true
    addi    $a0, $a0, 1
.num:
    lb      $t0, 0($a0)
    slti    $t2, $t0, 58        # *str <= '9'
    slti    $t3, $t0, '0'       # *str < '0'
    beq     $t2, $zero, .done
    bne     $t3, $zero, .done
    sll     $t2, $v0, 1
    sll     $v0, $v0, 3
    add     $v0, $v0, $t2       # num *= 10, using: num = (num << 3) + (num << 1)
    addi    $t0, $t0, -48
    add     $v0, $v0, $t0       # num += (*str - '0')
    addi    $a0, $a0, 1         # ++num
    j   .num
.done:
    beq     $t1, $zero, .out    # if (isNegative) num = -num
    sub     $v0, $zero, $v0
.out:
    jr      $ra         # return

(Just like the C atoi() function, it's got no error-checking mechanism, you might want to add that).

Parse each individual number from the file (by passing it to atoi()) and store it in the array as an integer.