;----------RED-SECTOR-INC.-proudly-presents-a-33-year-old-record-:----------
; 455-byte footprint___ _ "...The original chess game in a bootsector"
; / / _____ _ _ _____ _ _ ___ _
; .::. / / / / / / / / / /
; :::: / / ____ .-/ _ ___/-. .-/ _ ___/-. / /__
; :: / \ | | . | | | . | / /
; :: __ _ \ l | | | l | | / ___/
; .::. / / / / | l |_| l | |__/ / ____
; .::::. / __/ `--' `--' / |
; :::::::: / / |
; ___ __ Cl! ___ ___ / ___ _ _ __|
; ___ _ _ / __/_ __ _ _/ _/_ _ /_ / / ___ /__
; /_/ / / / / / / _____/ / / / __/ _ / / /
; .-/ ___/ / /______ / ___\ \___ / / __/
; | / / / | __/ ___ | \ | ___\ \___
; | / ____ | / | | _/ | | \ |
; | /--/ | ___/ | | | | | _/ |
; | | / / :: | ____/ :: | | :: \_____| | |
; |_____/ :: | __/ /_______| /_______| |_______\ | :: \_____|
; /_______| /___ _ /___ _ _ ___\ |_______\
; /___ _ _ ___\ v.03
; BootChess is the smallest computer implementation of chess on any platform
;-BootChess.asm-------------------;-----------------------------------------
_b equ byte ; gui=1 x86=0 p2q=0 485b NO pad OK gui NO vbr+ NO queen
_w equ word ; gui=0 x86=1 p2q=1 479b+ OK pad NO gui OK vbr- OK queen
_d equ dword ; gui=0 x86=1 p2q=0 481b+ OK pad NO gui OK vbr+ NO queen
_s equ short ; gui=0 x86=0 p2q=1 487b NO pad NO gui NO vbr- OK queen
_f equ far ; gui=0 x86=0 p2q=0 468b NO pad NO gui NO vbr+ NO queen
org 100h ; start of com binary program ip
brd equ bf2+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-through
rle: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-caps
in2:mov si,br0 ; si points to endrank "rnbqkbnr" str
mov cL,8 ; "rnbqkbnr" endrank str length
in3: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 callers
ge0:mov bx,di ; physical board idx (bx=brd)
mov dh,'1' ; beg white move src rank
ge1:mov dl,'h' ; beg white move src file
ge2:mov [si],dx ; beg white move src str
mov ch,'1' ; beg white move dst rank
ge3:mov cl,'h' ; beg white move dst file
ge4: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 enough
wor: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-ply
lkj:dec si ; realign source index
dec si ; to copy dword bst=dword idx
movsd ; after 4096 tries : move=dword bst
mis: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 rank
cpx: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 move
val: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 conforming
opn:call ver ; di=brd, black move legal chess ?
jc bla ; white move not legal chess
jmp _s val ; validate black move
ver: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 king
sp3:jnp sp4 ; branch if piece not pawn (bit#4!=1)
add bx,bp ; pawn player turn unidirection mutex
sp4: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 ptr
vl2: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 move
sam: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 ?
jz _s bad ; illegal chess move is a miss
yes:pop cx ; correct entry sp and disregard count
retn ; return to caller(s)
ord:test ch,ch ; pawn piece vert move=;no eating ?
jz yes ; no eating=;empty dst sqr else illegal
dif: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 illegal
skp: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 remain
bad:pop cx ; restore piece type deltas
dec ch ; all possible delta nums verified ?
jnz vl1 ; if not then cont next delta type
nok:stc ; else return /w no match flg set
retn ; return to caller
key:call prt ; refresh screen to account input echo
xor bx,bx ; bx=str idx=odd/even/alpha/num mutex
kbd:cbw ; fun blocking wait for keystroke (ah=0)
int 16h ; std bios keybd api (ah=scan al=ascii)
car:mov [bx+si],al ; sav ascii val to move string (si=num)
prt:pusha ; save game state snapshot
mov si,bf2+16
mov cl,8
rows:mov ch,8
row:lodsb
int 29h
dec ch
jnz row
mov al,10
int 29h
add si,8
loop rows
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 idx
act: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 conforming
put: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 ?
prm: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 conforming
chk: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
xit:retn ; return to caller(s) nb: destroys ah
tab 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 trick
br0 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 reps
p db 2,3,-10h,-15,-17,10h,15 ; bit#2 pf=04 p[6]=r[0] overlay
r db 17,4,10h,-1h,-10h ; bit#3 ??=08 r[5]=n[0] overlay
n db 1,8,1fh,21h,12h,-0eh,-1fh ; bit#4 af=16 n[9]=b[0] overlay
db -21h,-12h ; ... end of knight moves list
b db 0eh,4,-0fh,11h,-11h ; bit#5 ??=32 b[5]=q[0] overlay
q db 0fh,8 ; bit#6 zf=64 k=q except k[0]=1
bf2 db 10h,11h,0fh,1h,-10h ; queen/king moves list and gui base
db -11h,-0fh,-1h ; ... end of queen/king moves list
num db "e2e4" ; hardcoded Ruy Lopez opening Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.
Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.
Every assembler may have it's own assembly language designed for a specific computers or an operating system.
Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.
Assembly language usually consists of three sections,
Data section
To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section
To declare variables
text section
_start specifies the starting of this section where the actually code is written.
There are various define directives to allocate space for variables for both initialized and uninitialized data.
variable-name define-directive initial-value
| Define Directive | Description | Allocated Space |
|---|---|---|
| DB | Define Byte | 1 byte |
| DW | Define Word | 2 bytes |
| DD | Define Doubleword | 4 bytes |
| DQ | Define Quadword | 8 bytes |
| DT | Define Ten Bytes | 10 bytes |
| Define Directive | Description |
|---|---|
| RESB | Reserve a Byte |
| RESW | Reserve a Word |
| RESD | Reserve a Doubleword |
| RESQ | Reserve a Quadword |
| REST | Reserve a Ten Bytes |
Constants can be defined using
CONSTANT_NAME EQU regular-exp or value
%assign constant_name value
%define constant_name value
Loops are used to iterate a set of statements for a specific number of times.
mov ECX,n
L1:
;<loop body>
loop L1
where n specifies the no of times loops should iterate.
Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.
procedure_name:
;procedure body
ret