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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 example, the number 1234 is stored as: 01 02 03 04H There are two instructions for processing these numbers: AAM - ASCII Adjust After Multiplication AAD - ASCII Adjust Before Division The four ASCII adjust instructions, AAA, AAS, AAM and AAD can also 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 After 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 main ;must be declared for using gcc main: ;tell linker entry point mov mov clc add_loop: mov adc aaa pushf or popf mov dec loop mov esi, 4 ;pointing to the rightmost digit ecx, 5 ;num of digits al, [num1 + esi] al, [num2 + esi] al, 30h [sum + esi], al esi add_loop edx,len ;message length TUTORIALS POINT Simply Easy Learning
mov ecx,msg ;message to write mov ebx,1 ;file descriptor (stdout) mov eax,4 ;system call number (sys_write) int 0x80 ;call kernel mov edx,5 ;message length mov ecx,sum ;message to write mov ebx,1 ;file descriptor (stdout) mov eax,4 ;system 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 Sum is:',0xa len equ $ - msg num1 db '12345' num2 db '23456' sum db ' ' When the above code is compiled and executed, it produces following result: The Sum is: 35801 TUTORIALS POINT Simply Easy Learning
Page 1 and 2:
Assembly Language Tutorial
Page 3 and 4:
ABOUT THE TUTORIAL Assembly Program
Page 5 and 6:
Table of Content Assembly Programmi
Page 7 and 8: The XOR Instruction ...............
Page 9 and 10: CHAPTER 1 Assembly Introduction Wha
Page 11 and 12: Main use of hexadecimal numbers in
Page 13 and 14: x: memory address When the processo
Page 15 and 16: Check The netwide assembler (NASM)
Page 17 and 18: ; This program displays a message o
Page 19 and 20: CHAPTER 4 Assembly Memory Segments
Page 21 and 22: CHAPTER 5 Assembly Registers Proces
Page 23 and 24: Control Registers The 32-bit instru
Page 25 and 26: CHAPTER 6 Assembly System Calls Sys
Page 27 and 28: Please enter a number: 1234 You hav
Page 29 and 30: Direct Memory Addressing When opera
Page 31 and 32: int 0x80 ;call kernel mov eax,1 ;sy
Page 33 and 34: Processor uses the little-endian by
Page 35 and 36: CHAPTER 9 Assembly Constants There
Page 37 and 38: The above code replaces PTR by [EBP
Page 39 and 40: dec [value] mov ebx, count inc word
Page 41 and 42: int 0x80 When the above code is com
Page 43 and 44: global main ;must be declared for u
Page 45 and 46: mov [res], ax mov ecx,msg mov edx,
Page 47 and 48: AND AL, 01H ; ANDing with 0000 0001
Page 49 and 50: The TEST Instruction The TEST instr
Page 51 and 52: L7: ... CMP is often used for compa
Page 53 and 54: jg _exit mov ecx, [num3] _exit: mov
Page 55 and 56: section .bss num resb 1 mov ecx, nu
Page 57: Such conversions are however, has a
Page 61 and 62: LODS - This instruction loads from
Page 63 and 64: mov ecx, len mov esi, s1 mov edi, s
Page 65 and 66: found! Repetition Prefixes The REP
Page 67 and 68: Example: The following example demo
Page 69 and 70: mov ecx, res mov edx, 1 mov ebx, 1
Page 71 and 72: CHAPTER 18 Assembly Recursion Arecu
Page 73 and 74: CHAPTER 19 Assembly Macros Writing
Page 75 and 76: CHAPTER 20 Assembly File Management
Page 77 and 78: Put the buffer size, i.e., the numb
Page 79 and 80: int 0x80 ;call kernel section .data
Page 81: mov eax, 1 xor ebx, ebx int 80h sec
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