Logic instructions

They are used to perform logic operations on the operators.

AND

NEG

NOT

OR

TEST

XOR

AND INSTRUCTION

Purpose: It performs the conjunction of the operators bit by bit.

Syntax:

AND destiny, source

With this instruction the "y" logic operation for both operators is carried out:

Source Destiny | Destiny

1 1 | 1

1 0 | 0

0 1 | 0

0 0 | 0

The result of this operation is stored on the destiny operator.

NEG INSTRUCTION

Purpose: It generates the complement to 2.

Syntax:

NEG destiny

This instruction generates the complement to 2 of the destiny operator and stores it on the same operator.

For example, if AX stores the value of 1234H, then:

NEG AX

This would leave the EDCCH value stored on the AX register.

NOT INSTRUCTION

Purpose: It carries out the negation of the destiny operator bit by bit.

Syntax:

NOT destiny

The result is stored on the same destiny operator.

OR INSTRUCTION

Purpose: Logic inclusive OR

Syntax:

OR destiny, source

The OR instruction carries out, bit by bit, the logic inclusive disjunction of the two operators:

Source Destiny | Destiny

1 1 | 1

1 0 | 1

0 1 | 1

0 0 | 0

TEST INSTRUCTION

Purpose: It logically compares the operators

Syntax:

TEST destiny, source

It performs a conjunction, bit by bit, of the operators, but differing from AND, this instruction does not place the result on the destiny operator, it only has effect on the state of the flags.

XOR INSTRUCTION

Purpose: OR exclusive

Syntax:

XOR destiny, source

Its function is to perform the logic exclusive disjunction of the two operators bit by bit.

Source Destiny | Destiny

1 1 | 0

0 0 | 1

0 1 | 1

0 0 | 0

4.5 Arithmetic instructions

They are used to perform arithmetic operations on the operators.

ADC

ADD

DIV

IDIV

MUL

IMUL

SBB

SUB

ADC INSTRUCTION

Purpose: Cartage addition

Syntax:

ADC destiny, source

It carries out the addition of two operators and adds one to the result in case the CF flag is activated, this is in case there is carried.

The result is stored on the destiny operator.

ADD INSTRUCTION

Purpose: Addition of the operators.

Syntax:

ADD destiny, source

It adds the two operators and stores the result on the destiny operator.

DIV INSTRUCTION

Purpose: Division without sign.

Syntax:

DIV source

The divider can be a byte or a word and it is the operator which is given the instruction.

If the divider is 8 bits, the 16 bits AX register is taken as dividend and if the divider is 16 bits the even DX:AX register will be taken as dividend, taking the DX high word and AX as the low.

If the divider was a byte then the quotient will be stored on the AL register and the residue on AH, if it was a word then the quotient is stored on AX and the residue on DX.

IDIV INSTRUCTION

Purpose: Division with sign.

Syntax:

IDIV source

It basically consists on the same as the DIV instruction, and the only difference is that this one performs the operation with sign.

For its results it used the same registers as the DIV instruction.

MUL INSTRUCTION

Purpose: Multiplication with sign.

Syntax:

MUL source

The assembler assumes that the multiplicand will be of the same size as the

multiplier, therefore it multiplies the value stored on the register given as operator by the one found to be contained in AH if the multiplier is 8 bits or by AX if the multiplier is 16 bits.

When a multiplication is done with 8 bit values, the result is stored on the AX register and when the multiplication is with 16 bit values the result is stored on the even DX:AX register.

IMUL INSTRUCTION

Purpose: Multiplication of two whole numbers with sign.

Syntax:

IMUL source

This command does the same as the one before, only that this one does take

into account the signs of the numbers being multiplied.

The results are kept in the same registers that the MOV instruction uses.

SBB INSTRUCTION

Purpose: Subtraction with cartage.

Syntax:

SBB destiny, source

This instruction subtracts the operators and subtracts one to the result if CF is activated. The source operator is always subtracted from the destiny.

This kind of subtraction is used when one is working with 32 bits quantities.

SUB INSTRUCTION

Purpose: Subtraction.

Syntax:

SUB destiny, source

It subtracts the source operator from the destiny.

Date: 2014-12-22; view: 758