BootChess in just 487 bytes

;----------RED-SECTOR-INC.-proudly-presents-a-33-year-old-record-:----------;                   ___ _;                  /     /         _____ _ _      _____ _ _        ___ _;     .::.        /     /         /     /  /     /     /  /       /     /;     ::::       /     / ____  .-/   _ ___/-. .-/   _ ___/-.     /     /__;      ::       /            \ |    |  .    | |    |  .    |    /        /;      ::            __ _     \     l  |    | |    l  |    |   /     ___/;     .::.    /     /   /     /     |  l    |_|    l  |    |__/     / ____;    .::::.        / __/            `--'           `--'            /      |;   ::::::::                /                               /             |;                    ___ __    Cl!   ___ ___ /      ___ _ _             __|;        ___ _ _    /   __/_ __  _ _/      _/_   _ /_  /  /        ___ /__;     /_/   /  / / /   / /            _____/ /  / /    __/      _ /   /  /;  .-/     ___/   /     /______         /      ___\    \___    / /    __/;  |      /      /     /       |     __/ ___  |    \       |  ___\    \___;  |     /  ____               |    /       | |   _/       | |    \       |;  |    /--/    |     ___/     |            | |            | |   _/       |;  |            |    /  /  ::  | ____/  ::  | |  ::  \_____| |            |;  |_____/  ::  | __/  /_______|    /_______| |_______\      |  ::  \_____|;       /_______|     /___ _       /___ _         _ ___\     |_______\;      /___ _                                                    _ ___\; BootChess is the smallest computer implementation of chess on any platform; Chess in a 512-byte x86 boot sector for Windows / Linux / OS X / DOS / BSD; Coded by Olivier "Baudsurfer/RSi" Poudade with extra help of Peter "QKumba"; Ferrie. Logo by Frederic "Cleaner/Break" Cambus. (c)2015 WTFPL v2 license. ; "Fasm BootChess.asm" + "partcopy BootChess.bin 0 200 -f0" = PC floppy boot ;-BootChess.asm-------------------;-----------------------------------------x86 equ 1                         ; x86=1 PC/emu vs. win32b/(DOS)Boxsaf equ 0                         ; saf=0 +queening -exotic failsafe _b equ byte                       ; DEFAULTS=PC FLOPPY BOOT+QUEENING_w equ word                       ; x86=1 saf=0 512b  inc.  queening _d equ dword                      ; x86=1 saf=1 500b+ excl. queening*_s equ short                      ; x86=0 saf=1 506b  inc.  queening  _n equ near                       ; x86=0 saf=0 487b  excl. queening_f equ far                        ; *only working version in Bochs    if x86                        ; beg of boot vs .com preprocessing    org 7c00h                     ; std start of bootsector after post    if saf                        ; beg clear any start ambiguous segment    jmp _f 0:fix                  ; 7c0:0000 vs. 0:7c000 cs para fix-up    end if                        ; end clear any start ambiguous segment  fix:push cs                       ; if post int 19h isr bootsrap loader     pop ds                        ; left any bda or shadow segment values     push cs                       ; then enforce ds=cs=0      pop es                        ; then enforce es=ds=cs=0    mov aX,13h                    ; function set vga mode 320x200x256    else                          ; else if 16-bit binary assume ah=0    org 100h                      ; start of com binary program ip    mov aL,13h                    ; function set vga mode 320x200x256    end if                        ; end of boot vs .com preprocessing    int 10h                       ; standard bios video api    brd equ bf1+16                ; chess board at end of sector    mov di,brd                    ; set physical board index    mov bp,12                     ; set 6x8+8 empty sqr mid board lines    call in2                      ; pass#1 black "rnbqkbnr" low-caps    push word opn                 ; pass#2 hi-caps whites & fall-throughrle:lodsb                         ; al='.'/al=null (fixed length rle)    mov cl,8                      ; empty sqr mid board line length    rep stosb                     ; set one empty sqr mid board line    dec bp                        ; all empty sqr mid brd lines inited ?    jnz rle                       ; if not repeat init else bp=0 assumed    mov ah,'A'-'a'                ; fall-through pass#2 white hi-capsin2:mov si,br0                    ; si points to endrank "rnbqkbnr" str    if x86=0                      ; if .com binary environment ch=0    mov cL,8                      ; "rnbqkbnr" endrank str length    else                          ; assume nothing although tempting     mov cX,8                      ; "rnbqkbnr" endrank str length    end if                        ; end of register ch startup valuein3:lodsb                         ; read physical board str car    add al,ah                     ; hi-caps rank 1 / low-caps rank 8    stosb                         ; write physical board str car    loop in3                      ; all "rnbqkbnr" str car written ?    mov cl,8                      ; si-;equiv piece vals di-;0x88 brd    rep movsb                     ; write logical 0x88 board str vals    retn                          ; return to callersge0:mov bx,di                     ; physical board idx (bx=brd)    mov dh,'1'                    ; beg white move src rankge1:mov dl,'h'                    ; beg white move src filege2:mov [si],dx                   ; beg white move src str    mov ch,'1'                    ; beg white move dst rankge3:mov cl,'h'                    ; beg white move dst filege4:mov [si+2],cx                 ; beg white move dst str    pusha                         ; save all values    call idx                      ; passive chess coords to linear indexes    jbe  mis                      ; white move src color not conforming    push bx                       ; save white move dst idx    call ver                      ; white move legal chess ?    pop bx                        ; restore white move dst idx    jc mis                        ; white move not legal chess    mov di,num+3                  ; compare move destination rank in 7dfeh     inc si                        ; with move source rank in 7dfch     cmpsb                         ; is taxi distance to topmost bettered ?     jnc wor                       ; else not getting closer to black king    cmp _b [di],'?'               ; does any fallback move exist yet ?    jz lkj                        ; no, then last valid move good enoughwor:mov aL,_b[si+bx+brd-num-'a'+6]; yes, previous valid legal exist so     dec aL                        ; only override if it's a capture     js mis                        ; no, don't want worse taxi distance      mov bx,fs                     ; it's a capture with piece value=al    cmp bL,aL                     ; but hightest capture value yet ?    jnc mis                       ; no, less important opponent piece max:mov fs,bx                     ; fs=best move yet in taxi half-plylkj:dec si                        ; realign source index     dec si                        ; to copy dword bst=dword idx     movsd                         ; after 4096 tries : move=dword bstmis:popa                          ; restore all values    cmp cl,'a'                    ; end white move dst file ?    loopnz ge4                    ; dec white move else next dst file    inc ch                        ; inc white move dst rank    cmp ch,'9'                    ; end white move dst rank ?    jnz ge3                       ; else next move dst rankcpx:inc bx                        ; inc physical board index    dec dx                        ; dec white move src file    cmp dl,'`'                    ; end white move src file ?    jnz ge2                       ; else next move src file    inc dh                        ; inc white move src rank    cmp dh,ch                     ; end white move src rank ? ch=9    jnz ge1                       ; else next move src rank    push _d [si+4]                ; get best white move found    pop _d [si]                   ; set it as final white moveval:mov cl,'.'                    ; valid : empty sqr replaces src piece    call act                      ; active chess coords to linear indexes    xor bp,3                      ; player turn and pawn unidir. delta    jz ge0                        ; white turn to play (case best=0)bla:mov al,'?'                    ; input str clear pattern    mov di,si                     ; input str clear pattern (di=num)    mov cx,8                      ; input str clear pattern    rep stosb                     ; input str clear pattern (di=brd)    call key                      ; get user keyboard input    jbe bla                       ; black move src color not conformingopn:call ver                      ; di=brd, black move legal chess ?    jc bla                        ; white move not legal chess    jmp _s  val                   ; validate black movever:call idx                      ; get lin indexes /w implicit passive    xchg bx,dx                    ; switch bx=dst idx dx=src idx    mov ah,[si+bx+brd-num-'a'+8]  ; get piece logical 0x88 brd val...    mov dh,bl                     ; dh=src idx dl=dst idx    sub dx,"aa"                   ; get move file zero-based indexes    bsr bx,ax                     ; scan for 1st bit set (si=idx+10)    movsx bx,[si+bx-10-num+tab]   ; bl=moved piece type idx (bh=0)    mov cx,_w [si+bx-num+tab]     ; piece type deltas cl=repeats ch=num    sahf                          ; set piece logical 0x88 brd val      jnp sp1                       ; branch if piece not pawn (bit#4!=1)    jc sp2                        ; branch if pawn prev moved (bit#0=1)sp1:jns sp3                       ; branch if piece not king (bit#7!=1)sp2:mov cl,1                      ; override repeat if piece pawn or kingsp3:jnp sp4                       ; branch if piece not pawn (bit#4!=1)    add bx,bp                     ; pawn player turn unidirection mutexsp4:inc bx                        ; advance piece type struct field ptr    and ah,11111100b              ; isolate piece bitmask only vl1:push cx                       ; save piece type deltas    mov al,dh                     ; load start dst idx val    inc bx                        ; advance piece type struct field ptrvl2:add al,[si+bx-num+tab]        ; add this piece delta to dst idx val    xchg aL,bL                    ; base reg=dst idx val and preserved    mov ch,[si+bx+brd-num+8]      ; read projected dst square val    xchg aL,bL                    ; base reg=piece type struct field ptr    cmp al,dl                     ; wanted move found (src+delta(s)=dst) ?    jnz dif                       ; different than requested movesam:sahf                          ; get piece logical 0x88 brd val in flgs    jnp yes                       ; branch if piece is not pawn (bit#2=0)    test [si+bx-num+tab],1        ; pawn piece delta parity=diag vs. vert    jz ord                        ; branch if pawn piece moving vert    test ch,ch                    ; pawn piece vert move=;eating ?    jnz yes                       ; capturing verify dst sqr not empty    jmp _s bad                    ; else illegal chess move is a missord:test ch,ch                    ; pawn piece vert move=;no eating ?    jz yes                        ; no eating=;empty dst sqr else illegaldif:sahf                          ; store piece nature in flags register    jnp skp                       ; not pawn piece so skip direction test    test [si+bx-num+tab],1        ; pawn piece delta parity=diag vs. vert    jnz bad                       ; diagonal pawn move is illegalskp:test ch,ch                    ; else skipping over dst square val ?    jnz bad                       ; projected dst sqr val is not empty    sahf                          ; get piece logical 0x88 brd val in flgs    jz x88                        ; branch if piece is queen (bit#6=1)    jna bad                       ; branch if piece is not knight(bit#4=0)x88:test al,88h                   ; ch=0 dst out of physical board limits?    loopz vl2                     ; else cont if delta repeats remainbad:pop cx                        ; restore piece type deltas    dec ch                        ; all possible delta nums verified ?    jnz vl1                       ; if not then cont next delta typenok:stc                           ; else return /w no match flg set    retn                          ; return to calleryes:pop cx                        ; correct entry sp and disregard count    retn                          ; return to caller(s)key:call prt                      ; refresh screen to account input echo    xor bx,bx                     ; bx=str idx=odd/even/alpha/num mutexkbd:cbw                           ; fun blocking wait for keystroke (ah=0)    int 16h                       ; std bios keybd api (ah=scan al=ascii)esc:dec ah                        ; was esc key pressed to quit ?    jnz car                       ; else default process key inputxit:if x86                        ; if x86 boot context environment    int 19h                       ; exit through bootstrap to reboot cpu    else                          ; else if .com 16-bit binary    int 20h                       ; dos 1+ - terminate program    end if                        ; end of exit methods (os load or shell)car:mov [bx+si],al                ; sav ascii val to move string (si=num)prt:pusha                         ; save game state snapshot    cwd                           ; curs location dx=(0,0)=(row,column)    mov ax,1301h                  ; function ega write str write mode 1    mov bl,7                      ; page 0 grey car attrib matching tty    mov cl,8                      ; src str lngth (curs updated horiz)    mov bp,bf1                    ; es:bp is "abcdefgh" ptrlns:int 10h                       ; standard bios video api    add bp,16                     ; bp=para step siz separating strings    push ax                       ; save old bios video api func params    mov ax,0e39h                  ; function teletype outp car=rank '9'    sub al,dh                     ; decrement right handside rank value    int 10h                       ; standard bios video api    pop ax                        ; restore old bios video api fx params    cmp dh,cl                     ; src str total (curs updated vert)    inc dh                        ; preemptive off-by-one allows 9 verts    jc lns                        ; all 9 brd gui row strings printed ?    mov bp,si                     ; 10th row tail bp=move coords, cl=8    int 10h                       ; standard bios video api    popa                          ; restore game state snapshot    inc bx                        ; test if any more keys ?    cmp bl,4                      ; frFR format input string    jc kbd                        ; else continue input idx:loop idx                      ; ch=0 passive call load src/dst lin idxact:mov si,num                    ; reinit si to point to coord input str.    mov bx,[si]                   ; bx=src coord (pass#1)    cbw                           ; empty sqr val in logical 0x88 board    call put                      ; place param passed as fun pass#1    mov dx,[si+2]                 ; bx=dst idx dx=src idx    xchg bx,dx                    ; fall-through for second pass    push word mat                 ; test for checkmate and conformingput:xchg ax,bx                    ; bx|dx=[num+di]+16*((8-'0')-[num+di+1])    aad -10h                      ; shl ah,4/sub al,ah/xor ah,ah    add al,80h                    ; bx|dx=al-640%256-16*ah    xchg ax,bx                    ; bx|dx=al+128-16*ah    jcxz sim                      ; active call request or simulation ?    if saf=0                      ; standard non-failsafe queening    cmp _b [si+3],'8'             ; validated dst rank is top-most ?        jz qq                         ; if so then promote pawn to queen    cmp _b [si+3],'1'             ; validated dst rank is bottom-most ?    jnz prm                       ; if not no pawn queening promotionqq: sahf                          ; store piece nature in flag register    jnp prm                       ; no pawn queening promotion      xor ah,01000110b              ; transform p to promoted queen    inc cx                        ; queen promotion p2q or P2Q    end if                        ; end of conditional queeningprm:xchg ah,[si+bx+brd-num-'a'+8] ; update piece logical 0x88 board val    xchg cl,[si+bx+brd-num-'a']   ; update piece physical board ascii val    or ah,1                       ; update piece moved once (bit#0)sim:retn                          ; return to caller(s)mat:sahf                          ; catured piece king and mate ?    js xit                        ; if piece is king then game is over    call chk                      ; move src color conforming ?    jnz nok                       ; move src color not conformingchk:xchg bx,dx                    ; src idx <- dst idx    mov al,[si+bx+brd-num-'a']    ; pass#1:src idx pass#2:dst idx di=brd    xor _b [si+len-num],8         ; self-modif 8/26 val=[1;8]/[a(A);z(Z)]    mov cl,-'a'                   ; assert black piece car interval    test bp,bp                    ; test whose turn it is to play    jnz lim                       ; assert white piece car interval    mov cl,-'A'                   ; al=ascii value cl=-(lower boundery)lim:xadd al,cl                    ; tmp=al+cl cl=al al=tmp +fall-trough    db 0d4h                       ; aam <self-modified value>len:db 12h                        ; ah=al/8 al%=8    mov al,cl                     ; al=restored ascii value    test ah,ah                    ; set/clear zf=0 success zf=1 failure    retn                          ; return to caller(s) nb: destroys ahtab db p-tab,r-tab,n-tab,b-tab    ; piece type mov offset array    db q-tab,q-tab                ; note original 1K ZX Chess q=k trickbr0 db "rnbqkbnr",8,16,32,64,128  ; end rank pattern + beg piece values    db 32,16,8,'p',4,'.',0,'.',0  ; end piece values + beg mid board reps    db '.',0,'.',0,'P',4          ; ... end mid board repsp   db 2,3,-10h,-15,-17,10h,15    ; bit#2 pf=04 p[6]=r[0] overlayr   db 17,4,10h,-1h,-10h          ; bit#3 ??=08 r[5]=n[0] overlayn   db 1,8,1fh,21h,12h,-0eh,-1fh  ; bit#4 af=16 n[9]=b[0] overlay    db -21h,-12h                  ; ... end of knight moves listb   db 0eh,4,-0fh,11h,-11h        ; bit#5 ??=32 b[5]=q[0] overlayq   db 0fh,8,10h,11h,0fh,1h,-10h  ; bit#6 zf=64 k=q except k[0]=1    db -11h,-0fh,-1h              ; ... end of queen/king moves listbf1 db "abcdefgh"                 ; gui file index stringnum db "e2e4"                     ; hardcoded Ruy Lopez opening    if saf and x86                ; x86 failsafe exotic boot environment    times 510-($-$$) db 0         ; nul padding if necessary    org 7df0h                     ; boot signature vbr/mbr standard offset    sig db 55h,0aah               ; magic number no-endian boot signature    end if                        ; end of conditional failsafe signature