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Pep/8 is a toy assembly language used in some universities for teaching the basics of assembly and low-level programming. Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>
435 lines
9.1 KiB
Plaintext
435 lines
9.1 KiB
Plaintext
; Reads a square from stdin, then computes whether it is a magic square or not.
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;
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; A Magic Square is a square following a specific set of rules, namely:
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; - The sum of each row must be the same as the sum of the diagonal
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; - The sum of the anti-diagonal must be the same as the sum of the diagonal
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; - The sum of each column must be the same as the sum of the diagonal
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;
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; If any column, row, or anti-diagonal does not follow the aformented rules,
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; the program will output its number to stdout.
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;
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; Columns are identified by a negative digit, ranging from -1 to -n
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; The anti-diagonal is identified by the number 0.
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; Finally, rows are identified by a positive integer, ranging from 1 to n.
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;
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; Formatting:
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; First a number `n` is read from Stdin, it will determine the size of the square
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; Then, enter the data for the square, `n` entries will be read
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; The data is sequentially added to the square in memory, from the upper-left corner
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; to the lower-right corner, in a zig-zag pattern
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;
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; Example:
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; 3
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; 4 9 3
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; 3 5 7
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; 8 1 6
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;
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; Limitation: Since there is no dynamic allocation, the size
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; of the square is capped at a maximum of 32*32.
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; Any size lower than 1 or higher than 32 will produce
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; an error and the termination of the program.
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;_start
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DECI sidelen, d
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LDA sidelen, d
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CPA 1, i
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BRLT sderror
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CPA 32, i
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BRGT sderror
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LDX sidelen, d
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CALL mult
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STA sqlen, d
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CALL fillsq
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LDA sidelen, d
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LDX square, i
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CALL diagsum
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STA dgsm, d
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CALL colsums
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LDA sidelen, d
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LDX square, i
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CALL cdiagsum
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CPA dgsm, d
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BREQ cnt
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DECO 0, i
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CHARO '\n', i
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cnt: STA cdsm, d
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CALL rowsums
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STOP
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el: .BLOCK 2
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; Length of a side of the square
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sidelen: .WORD 0
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; Total length of the square
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sqlen: .BLOCK 2
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; 32 * 32 square of integers
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square: .BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 255
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.BLOCK 8
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; Prints an error and terminates the program
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sderror: STRO stderr, d
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STOP
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; Parameters: A: Size of a side of the square
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; X: Base address of the square
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; cscolid: Identifier of the column (0-based)
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; Computes the sum of each column
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; If the sum is not the same as dgsm, its index will be printed (in negative form)
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;
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; Parameters: A: Size of a side of the square
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; X: Address of the square
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;
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; Return: void
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colsums:STA clsmsqsz, d
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STX clsmsqad, d
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SUBA 1, i
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STA clsmyp, d
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clssmlp:CPA 0 ,i
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BRLT clsmout
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STA cscolid, d
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LDA clsmsqsz, d
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LDX clsmsqsz, d
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CALL colsum
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CPA dgsm, d
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BREQ clsdecpt
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LDX clsmyp, d
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NEGX
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STX clsmyp, d
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DECO clsmyp, d
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CHARO '\n', i
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LDX clsmyp, d
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NEGX
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STX clsmyp, d
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clsdecpt: LDA clsmyp, d
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SUBA 1, i
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STA clsmyp, d
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BR clssmlp
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clsmout: RET0
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clsmsqad: .BLOCK 2
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clsmsqsz: .BLOCK 2
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clsmyp_: .BLOCK 2
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; Compute the sum of each row
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; Prints its index if the value does not match dgsum
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;
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; Parameters: A: Size of a side of the square
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; X: Address of the square
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;
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; Returns: void
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rowsums: STA maxrows, d
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STX rowssqad, d
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LDA 0, i
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STA tmprwsm, d
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STA rowid, d
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rwsmslp: CPA maxrows, d
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BRGE rwsmsout
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STA rwxpos, d
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LDA maxrows, d
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LDX rowssqad, d
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CALL rowsum
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CPA dgsm, d
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STA tmprwsm, d
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BREQ rwinccpt
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DECO rowid, d
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CHARO '\n', i
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rwinccpt: LDA rowid, d
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ADDA 1, i
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STA rowid, d
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BR rwsmslp
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rwsmsout: RET0
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; Number of rows to compute
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maxrows: .BLOCK 2
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; Square address
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rowssqad: .BLOCK 2
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; Current rowid
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rowid: .BLOCK 2
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; Current rowsum
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tmprwsm: .BLOCK 2
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; Gets an element at the indexes given as parameter
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; The square is supposed to contain only integers
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; No check will be made on the correctness of the indexes
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;
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; Parameters: A: Size of a side of the square (in elements)
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; X: Base address of the square
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; xpos: Position in X for the element (0-indexed)
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; ypos: Position in Y for the element (0-indexed)
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;
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; Return: A will contain the element
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;
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; Side-effects: Registers A and X will neither be saved nor restored upon call
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; ypos will be altered
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elemat: STX elsqaddr, d
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ASLA
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LDX xpos, d
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CALL mult
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STA xpos, d
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LDX ypos, d
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ASLX
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STX ypos, d
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ADDA ypos, d
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ADDA elsqaddr, d
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STA elsqaddr, d
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LDX elsqaddr, d
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LDA 0, x
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RET0
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; X-index in square (in elements)
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xpos: .BLOCK 2
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; Y-index in square (in elements)
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ypos: .BLOCK 2
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; Address to fetch elements at
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elsqaddr: .BLOCK 2
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; Fills the square with input from the user
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;
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; Pass via register A the number of inputs to be read
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fillsq: LDX 0, i
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filloop: SUBA 1, i
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CPA 0, i
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BRLT fillout
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DECI square, x
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ADDX 2, i
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BR filloop
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fillout: RET0
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; Computes the sum of the digits of a column
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; The square is supposed to contain integers only
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;
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; Parameters: A: Size of a side of the square
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; X: Base address of the square
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; cscolid: Identifier of the column (0-based)
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;
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; Return: A: Sum of the digits of the column
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colsum: STA csclsqsz, d
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STX csclsqad, d
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LDA 0, i
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STA csclsum, d
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STA csclxpos, d
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clsmloop: CPA csclsqsz, d
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BRGE colout
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LDA cscolid, d
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STA ypos, d
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LDA csclxpos, d
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STA xpos, d
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LDA csclsqsz, d
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LDX csclsqad, d
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CALL elemat
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ADDA csclsum, d
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STA csclsum, d
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LDA csclxpos, d
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ADDA 1, i
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STA csclxpos, d
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BR clsmloop
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colout: LDA csclsum, d
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RET0
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; Identifier of the column which sum is to be computed
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cscolid: .BLOCK 2
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; Temporary for x position
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csclxpos: .BLOCK 2
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; Base address of the square
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csclsqad: .BLOCK 2
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; Size of a side of the square
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csclsqsz: .BLOCK 2
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; Sum of the column
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csclsum: .BLOCK 2
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; Computes the sum of the digits of a row
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; The square is supposed to contain integers only
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;
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; Parameters: A: Size of a side of the square
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; X: Base address of the square
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; rwxpos: Row index (0-based)
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;
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; Returns: A: Sum of the digits of the row
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rowsum: STA rwsqsz, d
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STX rwbsqadr, d
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LDA 0,i
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STA rwsum, d
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STA rwypos, d
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rwsumlp: LDA rwypos, d
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CPA rwsqsz, d
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BRGE rwsumout
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STA ypos, d
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LDA rwxpos, d
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STA xpos, d
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LDA rwsqsz, d
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LDX rwbsqadr, d
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CALL elemat
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ADDA rwsum, d
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STA rwsum, d
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LDA rwypos, d
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ADDA 1, i
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STA rwypos, d
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BR rwsumlp
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rwsumout: LDA rwsum, d
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RET0
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; Square size (in elements)
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rwsqsz: .BLOCK 2
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; Square base address
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rwbsqadr: .BLOCK 2
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; Position of the row to compute
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rwxpos: .BLOCK 2
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; Current column visited
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rwypos: .BLOCK 2
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; Sum of the row
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rwsum: .BLOCK 2
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; Computes the sum for the antidiagonal of a square
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; The square is supposed to contain integers only
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;
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; Parameters: A: Size of a side of the square (elements)
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; X: Base address of the square
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;
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; Returns: A: Sum of the antidiagonal
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cdiagsum: STA cdsqsz, d
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SUBA 1,i
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STA cdtmpy, d
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LDA 0, i
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STA cdtmpx, d
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STA cdsum, d
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STX cdsqaddr, d
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cdiaglp: LDA cdtmpx, d
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STA xpos, d
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LDA cdtmpy, d
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STA ypos, d
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CPA 0, i
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BRLT cdout
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LDA cdsqsz, d
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LDX cdsqaddr, d
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CALL elemat
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ADDA cdsum, d
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STA cdsum,d
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LDA cdtmpx, d
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ADDA 1, i
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STA cdtmpx, d
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LDA cdtmpy, d
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SUBA 1, i
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STA cdtmpy, d
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BR cdiaglp
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cdout: LDA cdsum, d
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RET0
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; Temporary handle for square size (elements)
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cdsqsz: .BLOCK 2
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; Square address
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cdsqaddr: .BLOCK 2
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; Keep x address
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cdtmpx: .BLOCK 2
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; Keep y address
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cdtmpy: .BLOCK 2
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; Sum of antidiagonal
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cdsum: .BLOCK 2
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; Computes the sum for the diagonal of a square
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; The square is supposed to contain integers only
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;
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; Parameters: A: Size of a side of the square (elements)
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; X: Base address of the square
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;
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; Returns: A: Sum of the diagonal
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;
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diagsum: STA dsqsz, d
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STX dsqaddr, d
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LDA 0, i
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STA tmpsum, d
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STA curra, d
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dglp: CPA dsqsz, d
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BRGE dglpout
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STA xpos, d
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STA ypos, d
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LDA dsqsz, d
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LDX dsqaddr, d
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CALL elemat
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ADDA tmpsum, d
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STA tmpsum, d
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LDA curra, d
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ADDA 1, i
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STA curra, d
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BR dglp
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dglpout: LDA tmpsum, d
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RET0
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; Address of the square
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dsqaddr: .BLOCK 2
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; Size of a side of the square (elements)
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dsqsz: .BLOCK 2
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; Current value of the x and y indexes
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curra: .BLOCK 2
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; Sum of the values
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tmpsum: .BLOCK 2
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; Muliplies two ints
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;
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; Parameters:
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; Register A : Left part of the multiplication
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; Register X : Right part of the multiplication
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;
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; Return:
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; Register A : Result of the multiplication
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;
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; Side-effects:
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; Uses multmp as a temporary value
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mult: STA multmp, d
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LDA 0, i
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muloop: CPX 0, i
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BRLE mulout
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ADDA multmp, d
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SUBX 1, i
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BR muloop
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mulout: RET0
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; Temporary variable for mult function
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; Holds the initial value of A
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multmp: .WORD 0
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; For debugging purposes
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; Prints the content of the square to stdout
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;
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; Parameters: A: Size of a side
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; X: Base address of square
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;
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; Side-effects:
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; Consider variables sidesz, sqaddr, sqmaxa as local, they will be written
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; Registers A and X will not be saved nor restored upon call
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printsq: STA sidesz, d
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STX sqaddr, d
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LDX sidesz, d
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CALL mult
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ASLA
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ADDA sqaddr, d
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STA sqmaxa, d
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LDX sqaddr, d
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LDA 0, i
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priloop: DECO 0, x
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CHARO ' ', i
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ADDX 2, i
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CPX sqmaxa, d
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BREQ priout
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ADDA 1, i
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CPA sidesz, d
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BRLT priloop
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LDA 0, i
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CHARO '\n', i
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BR priloop
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priout: RET0
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; Size of a side of the square
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sidesz: .BLOCK 2
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; Address of the square
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sqaddr: .BLOCK 2
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; Maximum address to iterate upon
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sqmaxa: .BLOCK 2
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; ------------------ GLOBALLY ACCESSIBLE SYMBOLS -------------------- ;
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;
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; Sum of the diagonal for the square
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; Reference value for magic-square
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dgsm: .WORD 0
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; Sum of the counter-diagonal
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cdsm: .WORD 0
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; Input error string
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stderr: .ASCII "A number between 1 and 32 (both inclusive) must be entered as value for the size of the square for the program to work.\n\x00"
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.END
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