Objective: Learn memory organization/layout, data transfer concepts and instruct
ID: 3598819 • Letter: O
Question
Objective: Learn memory organization/layout, data transfer concepts and instructions, memory access modes, memory allocation, memory size, type and length operators, and single and nested loop instruction.
Requirements:
1. (5 points) Write an assembly program that does the following:
- Define the following value 0506030704080102h in the .data segment using the 64-bit unsigned identifier.
- Find the sum of its words using the PTR operator. The sum should be D17h.
- Store the result in the appropriate N-bit register.
- The direction of adding two words goes from left to right.
2. (5 points) Use a loop instruction with indirect addressing to reverse the elements of an array in place.
- Do not copy the elements to any other array.
- Use the SIZEOF, TYPE, and LENGTHOF operators to make the program as flexible as possible if the array size and type should be changed in the future.
- Use the XCHG instruction.
- The array’s elements are: B, A, D, C, F, E, H, G.
- The array’s elements after running the program should look like: A, B, C, D, E, F, G, H.
3. (5 points) Implement the following expression in assembly language:
for (i = 5; i > 0; i--)
{
for(j = 3; j > 0; j--)
{
y = i + j ;
}
}
- Assume I and j are 32-bit registers and y is a list.
Explanation / Answer
public basmain
basmain proc far
assume cs:cseg,ds:cseg,ss:nothing,es:nothing
push ds ; save ds
xor ax,ax
mov ds,ax ; ds=0
mov si,4f2h ; dos communications area
mov ax,es ; get psp seg
mov [si],ax ; save psp in dos comm area
pop ds ; restore ds
mov si,80h ; point to command line
mov ch,0
mov cl,[si] ; get length of command line
jcxz p025 ; it's zero
p010: inc si
mov al,[si] ; get char from command line
cmp al,'/' ; is it a slash?
jnz p020 ; no
mov ax,[si+1] ; get next 2 chars
cmp ax,':M' ; is it M: ?
jz p030 ; yes
cmp ax,':m' ; is it m: ?
jz p030 ; yes
p020: loop p010 ; check next char
p025: jmp p080 ; no /m: or /M: found
p030: ; found /m: or /M:
add si,3 ; point to first number
mov ax,0
mov bx,0
mov cx,10
p040: mov bl,[si] ; get character
cmp bl,'0' ; out of range?
jb p050 ; yes
cmp bl,'9' ; out of range?
ja p050 ; yes
sub bl,'0' ; convert to binary
mul cx ; multiply ax by 10
add ax,bx ; add new digit
inc si ; point to next char
jmp p040 ; continue
p050: ; got value in ax
cmp ax,64 ; less than 64K?
jb p060 ; yes - print msg
cmp ax,1024 ; greater than 1024K?
ja p060 ; yes - print msg
mov cl,6
sal ax,cl ; convert from KB to paragraphs (*64)
mov bx,es ; get psp
add bx,ax ; new top of memory
mov si,2 ; point to top of memory in psp
mov ax,[si] ; get current top of memory
cmp ax,bx ; is new setting larger?
jae p055 ; no
mov dx,offset msg2 ; yes - print msg
jmp p065
p055: mov [si],bx ; save new top of memory
jmp p080
p060: mov dx,offset msg1 ; print the message
p065: add dx,100h ; fudge for the psp
mov ah,9
int 21h
p080: jmp $$main ; jump to BASIC's start point
msg1 db 'Memory specification must be from 64 to 1024',7,10,13,'$'
msg2 db 'Unable to limit memory',7,10,13,'$'
basmain endp
cseg ends
end basmain ; must be a main program!
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