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In computer programming, an arithmetic shift is a shift operator, sometimes termed a signed shift. The two basic types are the arithmetic left shift and the arithmetic right shift. For binary numbers it is a bitwise operation that shifts all of the bits of its operand; every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in. Instead of being filled with all 0s, as in logical shift, when shifting to the right, the leftmost bit is replicated to fill in all the vacant positions.
x86 assembly language is a family of backward-compatible assembly languages, which provide some level of compatibility all the way back to the Intel 8008 introduced in April 1972. x86 assembly languages are used to produce object code for the x86 class of processors. Like all assembly languages, it uses short mnemonics to represent the fundamental instructions that the CPU in a computer can understand and follow. Compilers sometimes produce assembly code as an intermediate step when translating a high level program into machine code. Regarded as a programming language, assembly coding is machine-specific and low level. Assembly languages are more typically used for detailed and time critical applications such as small real-time embedded systems or operating system kernels and device drivers.
In software engineering, a spinlock is a lock which causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking if the lock is available. Since the thread remains active but is not performing a useful task, the use of such a lock is a kind of busy waiting. Once acquired, spinlocks will usually be held until they are explicitly released, although in some implementations they may be automatically released if the thread being waited on blocks, or "goes to sleep".
In computer programming, a bitwise operation operates on a bit string, a bit array or a binary numeral at the level of its individual bits. It is a fast and simple action, basic to the higher level arithmetic operations and directly supported by the processor. Most bitwise operations are presented as two-operand instructions where the result replaces one of the input operands.
The NEC V20 was a microprocessor made by NEC. It was both pin and object-code compatible with the Intel 8088, with an instruction set similar to that of the Intel 80188 with some extensions. The V20 was introduced in March 1984.
A status register, flag register, or condition code register (CCR) is a collection of status flag bits for a processor. Examples of such registers include FLAGS register in the x86 architecture, flags in the program status word (PSW) register in the IBM System/360 architecture through z/Architecture, and the application program status register (APSR) in the ARM Cortex-A architecture.
The Western Design Center (WDC) 65C02 microprocessor is an enhanced CMOS version of the popular nMOS-based 8-bit MOS Technology 6502. While the 65C02 fixed several problems in the original 6502 and added some new instructions, its main feature was greatly lowered power usage, on the order of 10 to 20 times less than the NMOS 6502 running at the same speed. The reduced power consumption made the 65C02 useful in portable computer roles and microcontroller systems in industrial settings. It has been used in some home computers, as well as in embedded applications, including medical-grade implanted devices.
A bit field is a data structure used in computer programming. It consists of a number of adjacent computer memory locations which have been allocated to hold a sequence of bits, stored so that any single bit or group of bits within the set can be addressed. A bit field is most commonly used to represent integral types of known, fixed bit-width.
Bit manipulation is the act of algorithmically manipulating bits or other pieces of data shorter than a word. Computer programming tasks that require bit manipulation include low-level device control, error detection and correction algorithms, data compression, encryption algorithms, and optimization. For most other tasks, modern programming languages allow the programmer to work directly with abstractions instead of bits that represent those abstractions. Source code that does bit manipulation makes use of the bitwise operations: AND, OR, XOR, NOT, and possibly other operations analogous to the boolean operators; there are also bit shifts and operations to count ones and zeros, find high and low one or zero, set, reset and test bits, extract and insert fields, mask and zero fields, gather and scatter bits to and from specified bit positions or fields. Integer arithmetic operators can also effect bit-operations in conjunction with the other operators.
Sign extension is the operation, in computer arithmetic, of increasing the number of bits of a binary number while preserving the number's sign (positive/negative) and value. This is done by appending digits to the most significant side of the number, following a procedure dependent on the particular signed number representation used.
In the x86 architecture, the CPUID instruction is a processor supplementary instruction allowing software to discover details of the processor. It was introduced by Intel in 1993 with the launch of the Pentium and SL-enhanced 486 processors.
The FLAGS register is the status register in Intel x86 microprocessors that contains the current state of the processor. This register is 16 bits wide. Its successors, the EFLAGS and RFLAGS registers, are 32 bits and 64 bits wide, respectively. The wider registers retain compatibility with their smaller predecessors.
In computer processors the carry flag is a single bit in a system status register/flag register used to indicate when an arithmetic carry or borrow has been generated out of the most significant arithmetic logic unit (ALU) bit position. The carry flag enables numbers larger than a single ALU width to be added/subtracted by carrying (adding) a binary digit from a partial addition/subtraction to the least significant bit position of a more significant word. It is also used to extend bit shifts and rotates in a similar manner on many processors. For subtractive operations, two (opposite) conventions are employed as most machines set the carry flag on borrow while some machines instead reset the carry flag on borrow.
In a computer processor the negative flag or sign flag is a single bit in a system status (flag) register used to indicate whether the result of the last mathematical operation produced a value in which the most significant bit was set. In a two's complement interpretation of the result, the negative flag is set if the result was negative.
In the x86 assembly language, the TEST instruction performs a bitwise AND on two operands. The flags SF, ZF, PF are modified while the result of the AND is discarded. The OF and CF flags are set to 0, while AF flag is undefined. There are 9 different opcodes for the TEST instruction depending on the type and size of the operands. It can compare 8-bit, 16-bit, 32-bit or 64-bit values. It can also compare registers, immediate values and register indirect values.
C# Open Source Managed Operating System (Cosmos) is a toolkit for building operating systems, written mostly in the programming language C# and small amounts of a high level assembly language named X#. Cosmos is a backronym, in that the acronym was chosen before the meaning. It is open-source software released under a BSD license.
The zero flag is a single bit flag that is a central feature on most conventional CPU architectures. It is often stored in a dedicated register, typically called status register or flag register, along with other flags. The zero flag is typically abbreviated Z or ZF or similar in most documentation and assembly languages.
In the C programming language, operations can be performed on a bit level using bitwise operators.
Intel microcode is microcode that runs inside x86 processors made by Intel. Since the P6 microarchitecture introduced in the mid-1990s, the microcode programs can be patched by the operating system or BIOS firmware to workaround bugs found in the CPU after release. Intel had originally designed microcode updates for processor debugging under its design for testing (DFT) initiative.
The Alternate Instruction Set (AIS) is a second 32-bit instruction set architecture found in some x86 CPUs made by VIA Technologies. On these VIA C3 processors, the second hidden processor mode is accessed by executing the x86 instruction ALTINST. If AIS mode has been enabled, the processor will perform a JMP EAX and begin executing AIS instructions at the address of the EAX register. Using AIS allows native access to the Centaur Technology-designed RISC core inside the processor.
References
- ↑ "BT – Bit Test" . Retrieved 2011-08-21.
- ↑ "BTS – Bit Test and Set" . Retrieved 2011-08-21.
- ↑ "BTR – Bit Test and Reset" . Retrieved 2011-08-21.
- ↑ "BTC – Bit Test and Complement" . Retrieved 2012-11-04.