Sorting least to greatest of five numbers

Question

I need to sort five numbers from least to greatest.

I have been struggling with this assignment for a Little Man computer simulator. I tried adding more loops for the addition of 2 input numbers, but it never worked.

Working sorter for 3 numbers:

         INP        // Read in the first value
         STA 91     // store it
         INP        // Read in the second value
         STA 92     // store it
         INP        // Read in the third value
         STA 93     // store it
         LDA 92     // LOOP 1, STEP 1:  
         SUB 91     // 
         BRP STEP2  // if r91 and r92 are in order, don't swap them
         LDA 92     // Begin swapping registers
         STA 99     // temp = r92
         LDA 91
         STA 92     // r92 = r91
         LDA 99
         STA 91     // r91 = temp
STEP2    LDA 93     // LOOP 1, STEP 2
         SUB 92
         BRP STEP3  // If r92 and r93 are in order, don't swap them
         LDA 93     // Begin swapping registers
         STA 99     // temp = r93
         LDA 92
         STA 93     // r93 = r92
         LDA 99
         STA 92     // r92 = temp
STEP3    LDA 92     // LOOP 2, STEP 1
         SUB 91
         BRP STEP4  // if r91 and r92 are in order, don't swap them
         LDA 92     // Begin swapping registers
         STA 99     // temp = r92
         LDA 91
         STA 92     // r92 = r91
         LDA 99
         STO 91     // r91 = temp
STEP4    LDA 91     // Write out the sorted values 
         OUT
         LDA 92
         OUT
         LDA 93
         OUT
         HLT        // stop

Answer 1

The existing code has three steps for comparison & potential swap. The first step compares the first 2 values, the second step compares the second 2 values, and the third is like the first: it compares again the first two values.

When you have an input of 5 values, you need a loop, as otherwise you cannot fit all the necessary comparisons in the available 100 mailboxes. For that you can use an algorithm like bubble sort, which also compares adjacent pairs of values:

• Step 1: compare values 1 and 2
• Step 2: compare values 2 and 3
• Step 3: compare values 3 and 4
• Step 4: compare values 4 and 5

The code for each step is like you already have it, except that you will also make note of whether a swap was performed. This will be an indication that all the above steps need to be repeated again.

The code you have included does not use labels, and it is really a pity that the comments need to give the name to the number, while most LMC simulators support labels.

Here is how it could work:

#input: 5 3 4 2 1
        INP
        STA NUM1
        INP 
        STA NUM2
        INP
        STA NUM3
        INP 
        STA NUM4
        INP
        STA NUM5
BEGIN   LDA ZERO
        STA DIRTY
        LDA NUM2
        SUB NUM1
        BRP STEP2
        LDA ONE
        STA DIRTY
        LDA NUM1
        STA TEMP
        LDA NUM2
        STA NUM1
        LDA TEMP
        STA NUM2
STEP2   LDA NUM3
        SUB NUM2
        BRP STEP3
        LDA ONE
        STA DIRTY
        LDA NUM2
        STA TEMP
        LDA NUM3
        STA NUM2
        LDA TEMP
        STA NUM3
STEP3   LDA NUM4
        SUB NUM3
        BRP STEP4
        LDA ONE
        STA DIRTY
        LDA NUM3
        STA TEMP
        LDA NUM4
        STA NUM3
        LDA TEMP
        STA NUM4
STEP4   LDA NUM5
        SUB NUM4
        BRP CHECK
        LDA ONE
        STA DIRTY
        LDA NUM4
        STA TEMP
        LDA NUM5
        STA NUM4
        LDA TEMP
        STA NUM5
CHECK   LDA DIRTY
        BRZ OUTPUT
        BRA BEGIN
OUTPUT  LDA NUM1
        OUT
        LDA NUM2
        OUT
        LDA NUM3
        OUT
        LDA NUM4
        OUT
        LDA NUM5
        OUT
        HLT
NUM1    DAT
NUM2    DAT
NUM3    DAT
NUM4    DAT
NUM5    DAT
DIRTY   DAT
TEMP    DAT
ONE     DAT 001
ZERO    DAT 000

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