Assembly Language 5

I. 8086 16-bit CPU registers

16 Registers: Ax,bx,cx,dx,ah,al,bh,bl,ch,cl,dh,dl,sp,bp,si,di
4 General-Purpose registers: AX,BX,CX,DX
8-bit General purpose register: AH,AL,BH,BL,CH,CL,DH,DL, high 8-bit and 8th-bit for general purpose registers.

SP: stack pointer register, pointing to the top of the stack
BP: pointer register, equivalent to SP
SI,DI: Variable address register, with BX,BP, [Bx+si],

Segment Registers: DS, SS, CS, ES
DS data segment, SS stack segment, CS instruction segment, ES extension segment

Conventions: 1. Function return values are saved in Microsoft Dynamics AX, 2. Loop count saved in CX

Two. 32-bit CPU register equals 8086CPU, front plus E
General Register: Eax,ebx,ecx,edx
Stack pointer register: ESP, EBP
Variable address register: Esi,edi
Segment Register: EDS, ESS, ECS, EES

Segment Register: EDS, ESS, ECS, EES
EDS data segment, ESS stack segment, ECS instruction segment, EES extension segment

Convention: 1. Function return value is saved in eax, 2. Loop count is saved in ECX

Program 0: Convert "AAA", "BBB", "CCC" to uppercase

1.C Language Implementation code:
Char st1[3][4]={"AAA", "BBB", "CCC"};
void Ctwodlg::onbnclickedbutton2 ()
{
for (int i=0; i<3; i++)
{
int cc = 0;
for (int j=0;j <3; j + +)
{
char s = st1[i][j] & 0x5f;
ST1[I][J] =s;
}
}
}
Disassembly :
238:char st1[3][4]={"AAA", "BBB", "CCC"};
239:void Ctwodlg::onbnclickedbutton2 ()
240: {
011d2920. Ebp//Save the EBP content for recovery after the call is finished
011d2921 8B EC mov ebp,esp//Set EBP pointer to top of stack
011d2923-EC Ten sub esp,10h//sp-10h
011d2926 4D F0 mov dword ptr [EBP-10H],ECX

242:for (int i=0; i<3; i++)
011d2929 C7 FC xx/xx mov dword ptr [i],0
011d2930 EB, jmp ctwodlg::onbnclickedbutton2+1bh (11D293BH)//Jump down 4 lines cmp dword ptr [i],3
011d2932 8B FC mov eax,dword ptr [i]//Save to register EAX
011d2935 C0 Add eax,1//Register plus 1
011d2938-FC mov dword ptr [I],eax//Put in memory unit
011d293b 7D FC, CMP dword ptr [i],3//dword PTR indicates a memory unit pointing to a 32b, and a size of 3
011d293f 7D jge ctwodlg::onbnclickedbutton2+61h (11d2981h)//greater than 3 to jump out of the loop
243: {
244:for (int j=0;j <3; j + +)
011d2941 C7 F8/xx/mov dword ptr [j],0
011d2948 EB, jmp ctwodlg::onbnclickedbutton2+33h (11D2953H)
011d294a 8B 4D F8 mov ecx,dword ptr [j]
011d294d C1 Add ecx,1
011d2950 4D F8 mov dword ptr [J],ECX
011d2953 7D F8 cmp dword ptr [j],3
011d2957 7D jge ctwodlg::onbnclickedbutton2+5fh (11D297FH)
245: {
246:char s = st1[i][j] & 0x5f;
011d2959 8B FC mov edx,dword ptr [i]
011d295c 8B F8 mov eax,dword ptr [j]
011d295f 0F be 8C movsx ecx,byte ptr st1 (1335650h) [eax+edx*4]
011d2967 E1 5F and ECX,5FH
011d296a 4D F7 mov byte ptr [s],cl
247:ST1[I][J] =s;
011d296d 8B FC mov edx,dword ptr [i]
011d2970 8B F8 mov eax,dword ptr [j]
011d2973 8A 4D F7 mov cl,byte ptr [s]
011d2976 8C (1335650h) [EAX+EDX*4],CL], ST1 mov byte ptr
248:}
011d297d EB CB jmp ctwodlg::onbnclickedbutton2+2ah (11D294AH)
249:}
011d297f EB B1 jmp ctwodlg::onbnclickedbutton2+12h (11d2932h)//Jump up to mov eax,dword ptr [i]
250:}
011d2981 8B E5 mov esp,ebp
011d2983 5D Pop Ebp//Recover EBP content
011d2984 C3 RET

2. Assemble the implementation code:

Assume Cs:code, Ds:data, Ss:stack
Data segment
DB ' AAAA '
DB ' bbbb '
DB ' CCCC '
DB ' dddd '
Data ends

stack segment ; Defines a segment that is used as a stack segment and has a capacity of 4 bytes
DW 0,0
Stack ends

Code segment
Start
MOV Ax,data
MOV Ds,ax
MOV bx,0
MOV cx,4

MOV Ax,stack
mov ss, ax
MOV sp,4

S:push CX ; stack the CX value of the outer loop
mov cx,4 ; CX set as the number of inner loops
MOV si,0

S1:mov Al,ds:[bx+si]
and al,1011111b
MOV Ds:[bx+si],al
Inc si
Loop S1
Add bx,10
Pop cx ; eject the original CX value from the top of the stack and restore the outer loop CX
loop s ; loop instruction with outer loops minus 1 of the count value in CX

MOV ax,4c00h
int 21h
Code ends
End Start

Program 1: Use the Si,di implementation to copy the string to the buffer behind it
Assume Cs:code, Ds:data

Data segment
DB ' Welcome to Shiyan '
DB ' ........... '
Data ends

Code segment

Start
MOV Ax,data
MOV Ds,ax

MOV cx,17
MOV di,0
MOV si,17

S:mov Al,ds:[di]
MOV Ds:[si],al
Add di,1
Add si,1
Loop s

MOV ax,4c00h
int 21h
Code ends
End Start

Simpler code
Assume Cs:code, Ds:data
Data segment
DB ' Welcome to Shiyan ...................... ... '
Data ends

Code segment
Start
MOV Ax,data
MOV Ds,ax
MOV cx,17
MOV di,0

S:mov Al,ds:[di]
MOV Ds:[di+17],al
Add di,1
Loop s

MOV ax,4c00h
int 21h
Code ends
End Start

An equivalent notation
Assume Cs:code, Ds:data
Data segment
DB ' Welcome to Shiyan ...................... ... '
Data ends

Code segment
Start
MOV Ax,data
MOV Ds,ax
MOV cx,17

MOV dx,0
MOV di,0
MOV si,0

S:mov Al,ds:[bx][di]
MOV Ds:[bx][si].17,al
Add di,1
Add si,1
Loop s

MOV ax,4c00h
int 21h
Code ends
End Start

Assembly Language 5