In computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 processor

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 the negative flag or sign flag is a single bit in a system status (flag) register used to indicate whether the result of last mathematic operation resulted in a value whose most significant bit was set. In a two's complement

Two's complement

The two's complement of a binary number is defined as the value obtained by subtracting the number from a large power of two...

 interpretation of the result, the negative flag is set if the result was negative.

For example, in an 8-bit signed number system, -37 will be represented as 1101 1011 in binary (the most significant bit is 1), while +37 will be represented as 0010 0101 (the most significant bit is 0).

The negative flag is changed in the x86

X86 architecture

The term x86 refers to a family of instruction set architectures based on the Intel 8086 CPU. The 8086 was launched in 1978 as a fully 16-bit extension of Intel's 8-bit based 8080 microprocessor and also introduced segmentation to overcome the 16-bit addressing barrier of such designs...

 series processors by the following instructions (referring to the Intel 80386

Intel 80386

The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...

 manual ):

• All arithmetic operations except multiplication and division;
• compare instructions (equivalent to subtract instructions without storing the result);
• Logical instructions - XOR, AND, OR;
• TEST
  TEST (x86 instruction)
  In the x86 assembly language, the TEST instruction performs a bitwise AND on two operands. The flags SF, ZF, PF, CF, OF and AF are modified while the result of the AND is discarded. There are 9 different opcodes for the TEST instruction depending on the type and size of the operands. It can compare...
  
  instructions (equivalent to AND instructions without storing the result).