Floating point versus fixed point: what are the pros/cons?

Question

Floating point type represents a number by storing its significant digits and its exponent separately on separate binary words so it fits in 16, 32, 64 or 128 bits.

Fixe

Answer 1

Fixed point is widely used in DSP and embedded-systems where often the target processor has no FPU, and fixed point can be implemented reasonably efficiently using an integer ALU.

In terms of performance, that is likley to vary depending on the target architecture and application. Obviously if there is no FPU, then fixed point will be considerably faster. When you have an FPU it will depend on the application too. For example performing some functions such as sqrt() or log() will be much faster when directly supported in the instruction set rather thna implemented algorithmically.

There is no built-in fixed point type in C or C++ I imagine because they (or at least C) were envisaged as systems level languages and the need fixed point is somewhat domain specific, and also perhaps because on a general purpose processor there is typically no direct hardware support for fixed point.

In C++ defining a fixed-point data type class with suitable operator overloads and associated math functions can easily overcome this shortcomming. However there are good and bad solutions to this problem. A good example can be found here: http://www.drdobbs.com/cpp/207000448. The link to the code in that article is broken, but I tracked it down to ftp://66.77.27.238/sourcecode/ddj/2008/0804.zip