Assembler commands for beginners low-level programmers

All commands can be executed only with the help of machine language. Assembler-commands – symbolic representation of that language. With it, write a small but a very fast program. But despite their size, the writing process is very labor intensive. Therefore the Assembly instructions used to interact with a hardware component, or when the program doesn't have memory. Therefore, the Assembly code is executed in the form of subroutines and integrates code of high level. Since the assembler may vary depending on the type of architecture, it is necessary to consider his specific case, this article is the architecture of the Win. But the description of commands of the assembler usually does not change much, and they can be used in microcontrollers and other electronics devices that use an assembler.

Arithmetic commands used in Assembly language

Despite such a paradox, as the universality, only 4 arithmetic Assembly instructions there are and can be used by programmers. Nevertheless, through them and created a high-level programming languages that run computers, appliances, cell phones, smartphones, laptops, etc. you can Work with them, and very successfully. The list of commands assembler takov:

• Slojenie;
• Wikimania;
• Umnojeniya;
• Delanie.

Zlozenie

Arithmetic, known since school. You need to take into account only the feature addition, which is associated with the representation of the numbers to add in the memory of the computer. General view of the operation is as follows:

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ADD <Ячейка1/Регистр1> <Ячейка2/ - Range2>

Command takes the number of cells, adds them together and writes the “Ячейку1”. Now about the conditions of the operation: both the number of cells must have the same size. If first is the case, then it is possible to add on all. If first comes the cell, then it is possible to add or immediate operand or register.

The Description of Assembly instructions and their implementation requires a more comprehensive approach than can provide one article. According to the Assembly instructions, in spite of their meager number, written so many books that have hundreds of pages. Therefore, despite the apparent ease, we recommend you to see more details describing the team's work, which will allow you to learn all the nuances for different architectures.

Subtraction

This operation is executed according to the same algorithm as the previous one. Even the record type commands like:

SUB <Ячейка1/Регистр1> <Ячейка2/ - Range2>

The Principle of counting is that of the number 1 is subtracted No. 2, and recorded at site # 1. Conditions of operation are the same as the conditions of passage of the addition operation.

Multiplication

If division and addition have the same commands as for unsigned and for signed numbers, then the multiplication and division for them, there are various algorithms. So, to multiply unsigned numbers, use a command such as:

MUL <operand>

Specified in the command operand is one of the factors. The place of the second factor and place the result of the operation are recorded in advance, depending on the size of the MUL in bytes. Their location – the subject of a separate article. For signed multiplication, use the command:

IMUL<operand No. 1>, <operand No. 2>

You Can find other variants of implementation, but this is more understandable and familiar. We specify two factor, and the result is the operand number 1. Thus as the operand No. 1 is definitely the register, and the operand number 2 – register or memory cell. But other options will also be described:

IMUL<operand No. 1>

IMUL<operand No. 1>> <operand No. 2>, <immediate operand>

IMUL<operand No. 1>, <immediate operand>

The First option is similar to the MUL on the device, so the rules for him can be attributed here. The second option allows you to explicitly specify the location – as a result, and cofactor. The third option specifies the register that will be the first factor in which will be placed the result of the multiplication. Under the immediate operand is implied by not specifying a particular register, and the number by which to multiply the operand.

Division

As mentioned above, are used to divide the two teams. For unsigned numbers use:

DIV <operand>

For signed integers, use the command:

For idiv <operand>

A Feature of the use of teams in the division is that use only the operand-the divisor, which acts as a register or a memory cell. Numerator the number always has a definite location that depends on the size of the number. Your place has, and the result of the operation.

According to the search definition, you can say the same thing about multiplication: requires a separate article, as the amount of information is very significant.

Useful conclusion

Also in the category of "relatively useful the Assembly instructions" should also include the command NEG <Cell/Register>. She takessign in the number that is in the operand. That's all, I hope that article has helped you understand arithmetic Assembly instructions.

Useful and the operations increment and decrementing (increasing or decreasing the operand by one). To increment the operand, you must specify the following command:

INC <operand>

For decremental, you should write:

DEC <operand>

The operand may be a memory cell or register. Exclusive benefits from these operations is that they take up less space than the same Assembly instructions offered by addition or subtraction.