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TYPE and SIZE Operators

TYPE and SIZE Operators. TYPE returns the size, in bytes of a single element of a data label (variable) LENGTH returns a count of the number of individual elements in a data label that uses the DUP operator SIZE returns the product of TYPE * LENGTH. TYPE.

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TYPE and SIZE Operators

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  1. TYPE and SIZE Operators • TYPE • returns the size, in bytes of a single element of a data label (variable) • LENGTH • returns a count of the number of individual elements in a data label that uses the DUP operator • SIZE • returns the product of TYPE * LENGTH Irvine, Kip R. Assembly Language For Intel-Based Computers

  2. TYPE TYPE returns the size attribute: .data myByte db 1,2,3,4 myWord dw 1000h,2000h,3000h myDouble dd 12345678h myQuad dq 1,2,3 .code mov ax,TYPE myByte ; 1 mov ax,TYPE myWord ; 2 mov ax,TYPE myDouble ; 4 mov ax,TYPE myQuad ; 8 Irvine, Kip R. Assembly Language For Intel-Based Computers

  3. LENGTH Returns a count of the number of individual elements in a data label that uses the DUP operator: .data myByte db 20 dup(?) myWord dw 5 dup(0) .code mov ax,LENGTH myByte ; 20 mov ax,LENGTH myWord ; 5 Irvine, Kip R. Assembly Language For Intel-Based Computers

  4. SIZE Returns TYPE multiplied by LENGTH: .data myByte db 20 dup(?) myWord dw 5 dup(0) .code mov ax,SIZE myByte ; 20 (20 * 1) mov ax,SIZE myWord ; 10 (5 * 2) Irvine, Kip R. Assembly Language For Intel-Based Computers

  5. JMP and LOOP Instructions • JMP is an unconditional jump to a code label • LOOP creates a counting loop, using CX as the default counter • LOOPD uses ECX as the counter register • LOOPW uses CX as the counter register • (only necessary in 32-bit mode programming) Irvine, Kip R. Assembly Language For Intel-Based Computers

  6. JMP: Distance Modifiers • JMP SHORT destination • +/- 127 bytes • JMP NEAR PTR destination • same code segment • (default in the small and compact memory models) • JMP FAR PTR destination • different code segment • (default in the large, medium, and huge memory models) Irvine, Kip R. Assembly Language For Intel-Based Computers

  7. JMP Example Label1: . . jmp Label1 Unconditional Transfer of control to a label: Irvine, Kip R. Assembly Language For Intel-Based Computers

  8. LOOP Instruction • Automatically uses CX as the counter • decrements it automatically • If CX > 0, LOOP transfers control to a label • otherwise, excecution drops through Irvine, Kip R. Assembly Language For Intel-Based Computers

  9. LOOP Example Task: sum the integers { 1,2,3,4,5 } mov cx,5 ; loop counter mov bx,1 ; value to be added mov ax,0 ; holds the sum L1: add ax,bx inc bx Loop L1 ; AX=000F, BX=0006, CX=0000 Irvine, Kip R. Assembly Language For Intel-Based Computers

  10. Indirect Addressing • Indirect Operands [si]. [di], [bx], [bp] • Based and Indexed Operands array[si], array[di], array[bx] • Base-Index Operands [bx+si], [bx+di] • Base-Index with Displacement array[bx+si], array[bx+di] Irvine, Kip R. Assembly Language For Intel-Based Computers

  11. Indirect Operand Example .data aString db "ABCDEFG“ .code mov bx,offset aString add bx,5 mov dl,[bx] Irvine, Kip R. Assembly Language For Intel-Based Computers

  12. Adding 8-bit Integers .data aList db 10h,20h,30h sum   db 0 .code mov bx,offset aList    mov al,[bx] ; AL = 10h inc bx add al,[bx] ; AL = 30h inc bx add al,[bx] ; AL = 60h mov si,offset sum ; get offset of sum mov [si],al ; store the sum If you want to paste a code example such as this into a program, remember that the code segment must always begin with the following statements: mov ax,@data mov ds,ax Irvine, Kip R. Assembly Language For Intel-Based Computers

  13. Adding 16-bit Integers .data wordList dw 1000h,2000h,3000h, 0 .code mov bx,offset wordList mov ax,[bx] ; first number add ax,[bx+2] ; second number add ax,[bx+4] ; third number mov [bx+6],ax ; store the sum Irvine, Kip R. Assembly Language For Intel-Based Computers

  14. 32-Bit Registers The .386 directive permits any of the following registers to be used as indirect operands: EAX, EBX, ECX, EDX, ESI, EDI, EBP .386 mov ax,[ebx+3] mov dl,string[edx] mov ecx,[esi] mov ebx,[eax] Irvine, Kip R. Assembly Language For Intel-Based Computers

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