Assembly language (Example with mapping from C++ to Assembly)
- 2. Introduction Each family of processors has its own set of instructions, These set of instructions are called 'machine language instructions. A processor understands only machine language instructions, which are strings of 1's and 0's. However, machine language is too obscure and complex for using in software development. So, the low-level ASSEMBLY LANGUAGE is designed for a specific family of processors that represents various instructions in symbolic code and a more understandable form.
- 3. Advantages of using Assembly Language It requires less memory and execution time; It allows hardware-specific complex jobs in an easier way It is suitable for time-critical jobs It is most suitable for writing interrupt service routines and other memory resident programs.
- 4. Assembly Language - Basic Syntax An assembly program can be divided into three sections: The DATA section is used for declaring initialized data or constants. This data does not change at runtime. You can declare various constant values, file names, or buffer size, etc., in this section. The BSS section is used for declaring variables. The TEXT section is used for keeping the actual code. This section must begin with the declaration global _start, which tells the kernel where the program execution begins.
- 5. Syntax of Assembly Language Statements Assembly language statements are entered one statement per line. Each statement follows the following format: Following are some examples of typical assembly language statements:
- 6. Registers General registers Control registers Segment registers Data registers Pointer registers Index registers
- 7. Data Register AX is the primary accumulator − It is used in input/output and most arithmetic instructions. For example, in multiplication operation, one operand is stored in EAX or AX or AL register according to the size of the operand. BX is known as the base register − As it could be used in indexed addressing. CX is known as the count register − As the ECX, CX registers store the loop count in iterative operations. DX is known as the data register − It is also used in input/output operations. It is also used with AX register along with DX for multiply and divide operations involving large values.
- 8. Pointer Registers Instruction Pointer (IP) − The 16-bit IP register stores the offset address of the next instruction to be executed. Stack Pointer (SP) − The 16-bit SP register provides the offset value within the program stack. Base Pointer (BP) − The 16-bit BP register mainly helps in referencing the parameter variables passed to a subroutine.
- 9. Index Registers Source Index (SI) − It is used as source index for string operations. Destination Index (DI) − It is used as destination index for string operations.
- 10. Flag Registers The FLAGs register is the status register in microprocessors that contains the current state of the processor: Overflow Flag (OF) - It indicates the overflow of a high-order bit (leftmost bit) of data after a signed arithmetic operation. Direction Flag (DF) - It determines left or right direction for moving or comparing string data Interrupt Flag (IF) - It determines whether the external interrupts like keyboard entry, etc., are to be ignored or processed. Sign Flag (SF) - It shows the sign of the result of an arithmetic operation
- 11. Flag Registers Continue… Zero Flag (ZF) - It indicates the result of an arithmetic or comparison operation Auxiliary Carry Flag (AF) - It contains the carry from bit 3 to bit 4 following an arithmetic operation; used for specialized arithmetic Parity Flag (PF) - It indicates the total number of 1-bits in the result obtained from an arithmetic operation Carry Flag (CF) - It contains the carry of 0 or 1 from a high-order bit (leftmost) after an arithmetic operation.
- 12. Assembly - Conditions Unconditional jump − This is performed by the JMP instruction. Conditional execution often involves a transfer of control to the address of an instruction that does not follow the currently executing instruction. Transfer of control may be forward, to execute a new set of instructions or backward, to re-execute the same steps. Conditional jump − This is performed by a set of jump instructions j<condition> depending upon the condition. The conditional instructions transfer the control by breaking the sequential flow and they do it by changing the offset value in IP.
- 13. Example C++ language Code Assembly language Code
- 14. Example English Term: Assigned the Result of sum of A multiplied by B plus 10. High-Level Language: Result = A * B + 10 Intel Assembly Language: mov eax, A mul B add eax, 10 mov Result, eax Intel Machine Language: A1 00404000 F7 25 00404004 83 C0 0A A3 00404008
- 15. Thank You !!!
Editor's Notes
- #3: Each personal computer has a microprocessor that manages the computer's arithmetical, logical, and control activities. for handling various operations such as getting input from keyboard, displaying information on screen and performing various other jobs.