00:29
myString: db 'HaZa CS is very helpful',0
x: db 15
y: db 12
This assembly language routine ReverseWordwise (str,x,y)
reverses the contents of this ASCII string, word-wise without using any temporary
array (in place). Following is the sample output for the given
string:
helpful very is CS HaZa
Also, only
string instructions have been
used for string processing (scanning/reading /writing).
Assembly Language
Code
[org 0x0100]
jmp start
clearScreen:
mov ax , 0xB800
mov es , ax
mov di , 0
mov ax , 0x0720
mov cx , 2000
rep stosw
ret
strlen:
push bp
mov bp , sp
push ax
push cx
push es
push di
les di , [bp+4]
mov cx , 0xFFFF
xor al , al
repne scasb
mov ax , 0xFFFF
sub ax , cx
dec ax
mov [bp+8] , ax
pop di
pop es
pop cx
pop ax
pop bp
ret 4
printStr: ;[BP+10]=string [BP+8]=strlen
[BP+6]=x-coordinate
[BP+4]=y-coordinate
push bp
mov bp , sp
push ax
push cx
push si
push di
push es
mov ax , 0xB800
mov es , ax
mov al , 80
mul byte[bp+4]
add ax , [bp+6]
shl ax , 1
mov di , ax
mov si , [bp+10]
mov cx , [bp+8]
mov ah , 0x07
print:
lodsb
stosw
loop print
pop es
pop di
pop si
pop cx
pop ax
pop bp
ret 8
ReverseAlphabets: ;[BP+6]=string [BP+4]=strlen
push bp
mov bp , sp
push ax
push cx
push dx
push si
push di
mov dx , 0
mov ax , [bp+4]
mov cx , 2
div cx
mov dx , ax
mov cx , 0
mov ax , ds
mov es , ax
mov si , [bp+6]
mov di , [bp+6]
workReverseAlphabets:
lodsb
add si , [bp+4]
sub si , 2
sub si , cx
sub si , cx
movsb
mov di , si
dec di
stosb
inc cx
cmp cx , dx
jnl
finishReverseAlphabets
mov si , [bp+6]
add si , cx
mov di , [bp+6]
add di , cx
jmp
workReverseAlphabets
finishReverseAlphabets:
pop di
pop si
pop dx
pop cx
pop ax
pop bp
ret
ReverseWordwise: ; [BP+10]=local variable [BP+8]=string
[BP+6]=x-coordinate
[BP+4]=y-coordinate
push bp
mov bp , sp
push ax
push bx
push cx
push dx
push si
push di
push es
mov di , [bp+8]
sub sp , 2
push ds
push di
call strlen
pop ax
mov [bp+10] , ax ;[BP+6]=strlen
push word [bp+8] ;push string
push word [bp+10] ;push strlen
call
ReverseAlphabets
add sp , 4
mov ax , ds
mov es , ax
mov di , [bp+8]
push di
mov al , ' '
mov cx , [bp+10]
reverseNext:
repne scasb
mov dx , [bp+10]
sub dx , cx
dec dx
pop bx
sub dx , bx
add dx , [bp+8]
push bx
jcxz size_inc
jmp proceed
size_inc:
inc dx
proceed:
push dx
call
ReverseAlphabets
jcxz Printing
pop dx
pop bx
add bx , dx
inc bx
push bx
jmp reverseNext
Printing:
add sp , 4 ;clears the stack
call clearScreen
push word [bp+8]
push word [bp+10]
push word [bp+6]
push word [bp+4]
call printStr
pop es
pop di
pop si
pop dx
pop cx
pop bx
pop ax
pop bp
ret 4
start:
sub sp , 2 ;local variable
push string
mov ax , 0
mov al , [posX]
push ax
mov al , [posY]
push ax
call ReverseWordwise
mov ax , 0x4c00
int 0x21
posX: db 15
posY: db 12
string:db
'HaZa CS is very helpful',0
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