initial commit
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195
armv6/tictactoe/tictactoe.s
Normal file
195
armv6/tictactoe/tictactoe.s
Normal file
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.global _start
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_start:
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BL _printboard
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_inputloop:
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BL _getdigit
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LDR R1, =firstmove
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STRB R0, [R1]
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BL _getdigit
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LDR R2, =firstmove
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LDRB R1, [R2]
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BL _isvalidmove
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CMP R2, #1
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BEQ _inputloop @ move was invalid, retry
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BL _checkwin @ check if move was a winning one
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CMP R0, #1
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BEQ _player_won
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LDR R1, =currentmove @ check if max moves exceeded
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LDRB R2, [R1]
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ADD R0, R2, #1
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CMP R0, #8
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BHI _tie_end @ max moves achieved, its a tie
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STRB R0, [R1]
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LDR R1, =currentplayer @ change active player
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LDRB R0, [R1]
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CMP R0, #79 @ '79' == 'O', player 1
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BEQ _setplayer2
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MOV R0, #79 @ set current player to 1
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STRB R0, [R1]
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B _start
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_setplayer2:
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MOV R0, #88 @ set current player to 2
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STRB R0, [R1]
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B _start
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_player_won:
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LDR R1, =currentplayer
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LDRB R0, [R1]
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LDR R1, =output_player_won
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ADD R2, R1, #7
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STRB R0, [R2] @ store the current player as winner
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MOV R2, #14
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BL _print
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B _end
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_tie_end:
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LDR R1, =output_tie
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MOV R2, #5
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BL _print
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_end:
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BL _printboard
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MOV R7, #1
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SWI 0
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_checkwin:
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MOV R0, #0
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_checkwin_iterate:
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LDR R2, =boardlines @ base ptr
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LDR R3, =board
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ADD R1, R2, R0 @ iteration offset
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LDRB R2, [R1], #1 @ index to check
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ADD R4, R2, R3
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LDRB R5, [R4] @ cell #1
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CMP R5, #95 @ stop if first cell is empty
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BEQ _checkwin_next_line
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LDRB R2, [R1], #1
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ADD R4, R2, R3
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LDRB R6, [R4] @ cell #2
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CMP R5, R6
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BNE _checkwin_next_line
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LDRB R2, [R1]
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ADD R4, R2, R3
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LDRB R7, [R4] @ cell #3
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CMP R5, R7
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BNE _checkwin_next_line
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B _checkwin_win
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_checkwin_next_line:
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ADD R1, R0, #3
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MOV R0, R1
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CMP R0, #21
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BLS _checkwin_iterate
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_checkwin_nowin:
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MOV R0, #0
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BX lr
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_checkwin_win:
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MOV R0, #1
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BX lr
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_isvalidmove: @ checks if the move in R0, R1 is valid and sets R2 accordingly
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MOV R3, #3
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MUL R2, R1, R3
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ADD R3, R0, R2
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LDR R4, =board
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ADD R2, R4, R3
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LDRB R3, [R2]
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CMP R3, #95 @ '95' == _ character, empty cell
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BEQ _isvalidmove_succ
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MOV R2, #1 @ error, cell already set, retry!
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BX lr
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_isvalidmove_succ:
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LDR R3, =currentplayer @ store the move in the board
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LDRB R4, [R3]
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STRB R4, [R2]
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MOV R2, #0 @ cell set
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BX lr
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_getdigit: @ Puts the first read char in R0
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MOV R3, lr @ backup lr ptr
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_getinput:
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LDR R1, =inputreq
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MOV R2, #6
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BL _print
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MOV R7, #3 @ syscall read
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MOV R0, #0 @ from kb device
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MOV R2, #2
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LDR R1, =input @ into
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SWI 0 @ interrupt to let sys handle the call
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LDR R1, =input
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LDRB R2, [R1]
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CMP R2, #48 @ ascii value of '0'
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BLS _getinput
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CMP R2, #51 @ ascii value of '3'
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BHI _getinput
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SUB R0, R2, #49 @ subtract ascii value of '1' to bring result into range 0 to 2
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MOV lr, R3 @ restore lr ptr
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BX lr @ Return
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_printboard:
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MOV R10, lr
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MOV R4, #0 @ row index (0, 3 or 6)
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_printboard_row:
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MOV R3, #0 @ value index (0, 1, 2)
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_printboard_nextvalue:
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ADD R1, R3, R4 @ calculate index
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LDR R0, =board
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ADD R2, R0, R1 @ get board array ptr
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LDRB R0, [R2] @ load board byte
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LDR R1, =output_row
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ADD R2, R1, R3 @ get row output str ptr
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STRB R0, [R2] @ store the player char in output str
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ADD R0, R3, #1 @ up the value counter
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MOV R3, R0
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CMP R3, #2 @ check if we should print the row
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BLS _printboard_nextvalue @ no, still 1 or more values to insert
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LDR R1, =output_row @ prepare to print the row
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MOV R2, #4
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BL _print @ print the row
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ADD R5, R4, #3 @ get next row
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MOV R4, R5
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CMP R4, #6 @ check if not on last row already
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BHI _printboard_end @ printed all 3 rows, quit
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B _printboard_row
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_printboard_end:
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BX R10
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_print: @ prints the message pointed at by R1 with size in R2
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MOV R7, #4 @ syscall write
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MOV R0, #1 @ to the screen
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SWI 0
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BX lr
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.data
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currentplayer:
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.byte 79
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currentmove:
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.byte 0x00
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.align 9
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board:
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.byte 95, 95, 95, 95, 95, 95, 95, 95, 95
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.align 24
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boardlines:
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.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 3, 6, 1, 4, 7, 2, 5, 8, 0, 4, 8, 6, 4, 2 @ 8 x 3
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firstmove:
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.byte 0x00
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endline:
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.ascii "\n"
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inputreq:
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.ascii "Input:" @6
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input:
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.ascii " "
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output_row:
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.ascii " \n" @4
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output_tie:
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.ascii "tie!\n" @5
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output_player_won:
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.ascii "player X won!\n" @ size 14, X at index 7
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