How To Move A Decimal Value Into A Register In Arm

Associates - Numbers

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Numerical data is generally represented in binary system. Arithmetic instructions operate on binary information. When numbers are displayed on screen or entered from keyboard, they are in ASCII form.

Then far, we have converted this input data in ASCII form to binary for arithmetic calculations and converted the upshot dorsum to binary. The post-obit code shows this −

department	.text    global _start        ;must be declared for using gcc 	 _start:	                ;tell linker entry point    mov	eax,'3'    sub     eax, '0' 	    mov 	ebx, 'four'    sub     ebx, '0'    add together 	eax, ebx    add	eax, '0' 	    mov 	[sum], eax    mov	ecx,msg	    mov	edx, len    mov	ebx,1	         ;file descriptor (stdout)    mov	eax,4	         ;system call number (sys_write)    int	0x80	         ;call kernel 	    mov	ecx,sum    mov	edx, 1    mov	ebx,1	         ;file descriptor (stdout)    mov	eax,iv	         ;system telephone call number (sys_write)    int	0x80	         ;call kernel 	    mov	eax,ane	         ;system call number (sys_exit)    int	0x80	         ;phone call kernel 	 section .information msg db "The sum is:", 0xA,0xD  len equ $ - msg    segment .bss sum resb i        

When the above code is compiled and executed, it produces the following result −

The sum is: 7        

Such conversions, however, have an overhead, and associates linguistic communication programming allows processing numbers in a more than efficient way, in the binary form. Decimal numbers can exist represented in two forms −

• ASCII form
• BCD or Binary Coded Decimal form

ASCII Representation

In ASCII representation, decimal numbers are stored as string of ASCII characters. For example, the decimal value 1234 is stored every bit −

31	32	33	34H        

Where, 31H is ASCII value for 1, 32H is ASCII value for 2, so on. In that location are four instructions for processing numbers in ASCII representation −

• AAA − ASCII Adjust After Addition

• AAS − ASCII Adjust Afterwards Subtraction

• AAM − ASCII Suit Subsequently Multiplication

• AAD − ASCII Conform Earlier Division

These instructions exercise not have any operands and presume the required operand to be in the AL register.

The post-obit example uses the AAS instruction to demonstrate the concept −

section	.text    global _start        ;must be declared for using gcc 	 _start:	                ;tell linker entry indicate    sub     ah, ah    mov     al, '9'    sub     al, '3'    aas    or      al, 30h    mov     [res], ax 	    mov	edx,len	        ;message length    mov	ecx,msg	        ;message to write    mov	ebx,one	        ;file descriptor (stdout)    mov	eax,iv	        ;arrangement call number (sys_write)    int	0x80	        ;telephone call kernel 	    mov	edx,1	        ;message length    mov	ecx,res	        ;message to write    mov	ebx,one	        ;file descriptor (stdout)    mov	eax,4	        ;organization call number (sys_write)    int	0x80	        ;call kernel 	    mov	eax,1	        ;system call number (sys_exit)    int	0x80	        ;call kernel 	 section	.data msg db 'The Upshot is:',0xa	 len equ $ - msg			 section .bss res resb one        

When the above lawmaking is compiled and executed, information technology produces the following result −

The Result is: half dozen        

BCD Representation

There are two types of BCD representation −

• Unpacked BCD representation
• Packed BCD representation

In unpacked BCD representation, each byte stores the binary equivalent of a decimal digit. For instance, the number 1234 is stored as −

01	02	03	04H        

In that location are two instructions for processing these numbers −

• AAM − ASCII Adjust Afterwards Multiplication

• AAD − ASCII Adjust Before Division

The four ASCII arrange instructions, AAA, AAS, AAM, and AAD, can as well be used with unpacked BCD representation. In packed BCD representation, each digit is stored using four bits. Two decimal digits are packed into a byte. For example, the number 1234 is stored as −

12	34H        

There are two instructions for processing these numbers −

• DAA − Decimal Adjust Afterwards Addition

• DAS − decimal Adjust After Subtraction

There is no support for multiplication and division in packed BCD representation.

Example

The following program adds up two 5-digit decimal numbers and displays the sum. It uses the above concepts −

section	.text    global _start        ;must exist alleged for using gcc  _start:	                ;tell linker entry indicate     mov     esi, 4       ;pointing to the rightmost digit    mov     ecx, five       ;num of digits    clc add_loop:      mov 	al, [num1 + esi]    adc 	al, [num2 + esi]    aaa    pushf    or 	al, 30h    popf 	    mov	[sum + esi], al    dec	esi    loop	add_loop 	    mov	edx,len	        ;message length    mov	ecx,msg	        ;message to write    mov	ebx,1	        ;file descriptor (stdout)    mov	eax,4	        ;system call number (sys_write)    int	0x80	        ;telephone call kernel 	    mov	edx,five	        ;message length    mov	ecx,sum	        ;message to write    mov	ebx,ane	        ;file descriptor (stdout)    mov	eax,4	        ;system phone call number (sys_write)    int	0x80	        ;call kernel 	    mov	eax,1	        ;system call number (sys_exit)    int	0x80	        ;telephone call kernel  section	.data msg db 'The Sum is:',0xa	 len equ $ - msg			 num1 db '12345' num2 db '23456' sum db '     '        

When the above code is compiled and executed, it produces the post-obit result −

The Sum is: 35801        

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Source: https://www.tutorialspoint.com/assembly_programming/assembly_numbers.htm

Posted by: hullfurepought.blogspot.com

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