computer processor Cryptominer, In computing and computer science, a processor or processing unit is an electrical component (circuit (computer science), digital circuit) that performs operations on an external data source, usually Memory (computing), memory or som ...

s the parity flag indicates if the numbers of set bits is odd or even in the binary representation of the result of the last operation. It is normally a single bit in a processor status register. For example, assume a machine where a set parity flag indicates even parity. If the result of the last operation were 26 (11010 in binary), the parity flag would be 0 since the number of set bits is odd. Similarly, if the result were 10 (1010 in binary) then the parity flag would be 1. Some

microcontroller A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...

s, notably the ubiquitous 8051, include a parity flag to help with implementing

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

and other

serial communication In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits a ...

protocols, in lieu of a

UART A universal asynchronous receiver-transmitter (UART ) is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to ...

with parity support.

x86 processors

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

processors include a parity flag because they are descended (via the

Intel 8086 The 8086 (also called iAPX 86) is a 16-bit computing, 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-b ...

8080 The Intel 8080 is Intel's second 8-bit microprocessor. Introduced in April 1974, the 8080 was an enhanced successor to the earlier Intel 8008 microprocessor, although without binary compatibility.'' Electronic News'' was a weekly trade newspa ...

and 8008) from the

Datapoint 2200 The Datapoint 2200 was a mass-produced programmable terminal usable as a computer, designed by Computer Terminal Corporation (CTC) founders Phil Ray and Gus Roche and announced by CTC in June 1970 (with units shipping in 1971). It was initially ...

terminal, which was designed for serial communication duties. In x86 processors, the parity flag reflects the parity of only the ''

least significant byte In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a binary integer representing the lowes ...

'' of the result, and is set if the number of set bits of ones is even (put another way, the parity bit is set if the sum of the bits is even). According to the

Intel 80386 The Intel 386, originally released as the 80386 and later renamed i386, is the third-generation x86 architecture microprocessor from Intel. It was the first 32-bit computing, 32-bit processor in the line, making it a significant evolution in ...

manual, the parity flag is changed in the x86 processor family by the following instructions: * All arithmetic instructions; * Compare instruction (equivalent to a subtract instruction without storing the result); * Logical instructions - XOR, AND, OR; * the

TEST Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film) ...

instruction (equivalent to the AND instruction without storing the result). * Instructions which write to the entire flags register: POPF, IRET, interrupts, or any other instruction which causes a hardware task switch. The parity flag is tested by conditional jump instructions; the JP instruction jumps to the given target when the parity flag is set and the JNP instruction jumps if it is not set. The flag may be also read directly with instructions such as PUSHF, which pushes the flags register on the stack. One common reason to test the parity flag is to check an unrelated x87-FPU flag. The FPU has four condition flags (C0 to C3), but they can not be tested directly, and must instead be first copied to the flags register. When this happens, C0 is placed in the

carry flag In computer processors, the carry flag (usually indicated as the C flag) is a single bit in a system status register A status register, flag register, or condition code register (CCR) is a collection of status Flag (computing), flag bits for a ...

, C2 in the parity flag and C3 in the zero flag.{{cite web , url=http://www.intel.com/products/processor/manuals/index.htm , title=Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture , date=January 2011 , pages=97–98 The C2 flag is set when e.g. incomparable

floating point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a signed sequence of a fixed number of digits in some base) multiplied by an integer power of that base. Numbers of this form ...

values ( NaN or unsupported format) are compared with the FUCOM instructions.

x86 processors

References

See also