CODEWITHSUNDEEP
assemblydosx86-16tasm
Chanchal Roshan
Chanchal Roshan

Reputation: 174

Rotate count out of Range error

I am new to assembly language programming.
Can anyone figure out where I am going wrong?
The error while assembling is

Rotate count out of Range error
Error is at line: rol bl, 04

This is my code:

disp macro var
    lea dx, var
    mov ah, 09H
    int 21H
endm

ending macro
    mov ah, 4cH
    int 21H
endm

.model small
.stack 100H
.data
        msg1 db 10, 13, "_____STRING OPERATION_____$"
        msg2 db 10, 13, "1.Length", 10, 13, "2.Reverse $"
        msg3 db 10, 13, "3.Exit", 10, 13, "--->$"
        error db 10, 13, "Enter a valid choice ",10, 13, "$"
        msg4 db 10, 13, "Enter the string: $"
        msg5 db 10, 13, "Length of the string: $"
        msg6 db 10, 13, "Reversed String: $"
        choice db ?
        str1 db 20, ?, 20 dup(0)
.code
        mov ax, @data
        mov ds, ax

menu:   disp msg1
        disp msg2
        disp msg3

        mov ah, 01H
        int 21H
        mov choice, al

        cmp choice, 31H
        je str_len
        cmp choice, 32H
        je Reverse
        cmp choice, 33H
        je Exit
        disp error
        jmp menu

str_len:disp msg4
        mov ah, 0aH
        lea dx, str1
        int 21H

        disp msg5

        lea si, str1[1]
        mov bl, [si]
        mov cl, 02
back:   rol bl, 04
        mov dl, bl

        mov ah, 02H
        int 21H
        loop back

        ending

Reverse:

Exit:   ending

end

Upvotes: 0

Views: 2244

Answers (2)

Govind Parmar
Govind Parmar

Reputation: 21552

Real mode has a lot more limitations than protected mode about which registers do what and which instructions are valid. If you're used to programming in protected mode and long mode you should probably become familiar with these restrictions.

Another really commonly encountered restriction is that only the registers BX and BP are valid as base address offsets; the instruction 00 00 (add byte ptr [eax], al) in protected mode becomes add [bx+si], al in real mode, for example.

If the amount you are rotating by is not exactly 1, you need to put the count in CL and use that as the second operand for the ro[l|r] instruction - immediate values other than 1 are not valid.

Upvotes: 0

David Hoelzer
David Hoelzer

Reputation: 16351

The ROR and ROL instructions in the 8086 instruction set take either an immediate value of 1 or a count stored in CL. To rotate 4 bits, you would need to do this:

 MOV  CL, 4
 ROR  BL, CL

Upvotes: 4

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