Hi Daniweb,
I am working on an assignment that is aimed to help us understand floating points. The current task is to take a number as input, example 3.5, or 2.25 etc and output it as a binary decimal, ex 11.100000000, 10.0100000000.

To do this, I am taking the whole number and floating point seperately, converting them seperately and storing them seperately. The whole number part is working ok, however an issue is coming with the decimal part:

I am inputting it as a string, so .25 would be inputted as "25". I then convert it to binary by:

1) loading the first character into a register, say, $t0
2) subtracting 48 from it to get the decimal equavalent, so '2' becomes 2
3) loading the next character into, say, $t1
4) if the next character is either $zero (null character) or 10 (newline character), skip to step 10
5) $t3 contains 10, and this step it is multiplied by 10
6) repeat step 2 on $t1
7) multiplying the number in $t0 by 10, so $t0 becomes 2x10 = 20
8) adding $t0 to $t1 so it becomes 25
9) go back to step 3
10)multiply the number in t0 by 2
11)if the result is greater than the number in $t3 (in this case 50<100), store a 1 in memory. Else, store a 0

I also have a counter to enforce a maximum number of decimal places in binary

The problem that is arising is that when the QtSpim simulator comes to step 4, and is supposed to be loading the newline character, the number that comes in the register is 49. Hence it doesnt break out of the loop when its supposed to.

Can someone tell me whats going on? heres my code for input and conversion of the floating part of the numbers:

    la $s1, firstdecfl

    addi $v0, $zero, 8
    add $a0, $zero, $s1
    addi $a1, $zero, 4
    syscall         #input decimal part, take no more than 3 digits, store in firstdec


    addi $t6, $zero, 20 #max num of dec places

#first we need to merge the character array into a number
    la $t5, newline
    lb $t5, 0($t5)      #t5 contains newline

    la $s3, firstbinfl  #$s3 points to character array that will hold binary notation floating point 
    la $s1, firstdecfl  #s1 points to char array that holds decimal notation floating point

    lb $t0, 0($s1)      #bring the nextfloat character into register
    addi $t0, $t0, -48  #convert it to number

        addi $t3, $zero, 10 #to compare if decimal values have exceeded two places, and also used to check for newline(=10) character, as well as multiply while merging
    addi $s1, $s1, 1    #move to next char
    addi $t4, $zero, 10 #will be 10^n where n is number of decimal places, or digits in firstdecl. Will be used to divide the dec floating point

    lb $t2, 0($s1)

    beq $t2, $t5    firstflconv
    beq $t2, $zero, firstflconv

    mult $t3, $t4
    mflo $t4

    addi $t2, $t2, -48  #else repeat for the one after that 

    mult $t0, $t3   #multiply the first digit by 10
    mflo $t1
    add $t1, $t1, $t2   #and add the second digit to it, so '2', '5' will become 2*10+5 = 25, store in t0

    addi $s1, $s1, 1
    add $t0, $zero, $t1
    j concat

    beq $t6, $zero, printdot
    sll $t0, $t0, 1     #multiply by two
    bge $t0, $t4, storeone 

    addi $t6, $t6, -1
    addi $t5, $zero, 48 
    sb $t5, 0($s3)      #store '0'
    addi $s3, $s3, 1    #move pointer to next byte

    blt $t0, $t4, firstflconv

    addi $t6, $t6, -1
    addi $t5, $zero, 49
    sb $t5, 0($s3)      #store '1'
    addi $s3, $s3, 1

    div $t0, $t4
    mfhi $t0        #restandardize the comparison numbers
    blt $t0, $t4, firstflconv


    addi $t6, $zero, 20 #max dec places again
    la $s3, firstbinfl
    addi $a0, $zero, 46
    addi $v0, $zero, 11

    addi $v0, $zero, 11
    lb $a0, 0($s3)
    addi $s3, $s3, 1
    addi $t6, $t6, -1   #reduce counter
    bne $t6, $zero, printdecs

Edited by pspwxp fan

2 Years
Discussion Span
Last Post by pspwxp fan

Alright turns out there is no problem in this code. There was a problem with how i was storing my strings. The SPIM compiler was storing them in adjacent memory bytes as i had initialized them as

num1 .asciiz ""
num2 .asciiz ""

and somewhere between the first two snippets of code above, I was changing a value using a register that I thought was pointing to num1, however since num2 was right next to it, and it had recently incremented, it actually changed the value of num2. The solution was just to increase the spaces between the quotes in the initialization :)

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