|
A floating-point unit (FPU, colloquially a math coprocessor) is a part of a computer system specially designed to carry out operations on floating point numbers. Typical operations are addition, subtraction, multiplication, division, square root, and bitshifting. Some systems (particularly older, microcode-based architectures) can also perform various transcendental functions such as exponential or trigonometric calculations, though in most modern processors these are done with software library routines. In general purpose computer architectures, one or more FPUs may be integrated with the central processing unit; however many embedded processors do not have hardware support for floating-point operations. When a CPU is executing a program that calls for a floating-point operation, there are three ways to carry it out: * A floating-point unit emulator (a floating-point library) * Add-on FPU * Integrated FPU Some systems implemented floating point via a coprocessor rather than as an integrated unit. This could be a single integrated circuit, an entire circuit board or a cabinet. Where floating-point calculation hardware has not been provided, floating point calculations are done in software, which takes more processor time but which avoids the cost of the extra hardware. For a particular computer architecture, the floating point unit instructions may be emulated by a library of software functions; this may permit the same object code to run on systems with or without floating point hardware. Emulation can be implemented on any of several levels: in the CPU as microcode (not a common practice), as an operating system function, or in user space code. When only integer functionality is available the CORDIC floating point emulation methods are most commonly used. In most modern computer architectures, there is some division of floating-point operations from integer operations. This division varies significantly by architecture; some, like the Intel x86 have dedicated floating-point registers, while some take it as far as independent clocking schemes. Floating-point operations are often pipelined. In earlier superscalar architectures without general out-of-order execution, floating-point operations were sometimes pipelined separately from integer operations. Since the early and mid-1990s, many microprocessors for desktops and servers have more than one FPU. == Floating-point library == Some floating-point hardware only supports the simplest operations - addition, subtraction, and multiplication. But even the most complex floating-point hardware has a finite number of operations it can support - for example, none of them directly support arbitrary-precision arithmetic. When a CPU is executing a program that calls for a floating-point operation that is not directly supported by the hardware, the CPU uses a series of simpler floating-point operations. In systems without any floating-point hardware, the CPU emulates it using a series of simpler fixed-point arithmetic operations that run on the integer arithmetic logic unit. The software that lists the necessary series of operations to emulate floating-point operations is often packaged in a floating-point library. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Floating-point unit」の詳細全文を読む スポンサード リンク
|