Fixed-Point Blockset

Radix Point Interpretation

The radix point is the means by which fixed-point numbers are scaled. It is usually the software that determines the radix point. When performing basic math functions such as addition or subtraction, the hardware uses the same logic circuits regardless of the value of the scale factor. In essence, the logic circuits have no knowledge of a scale factor. They are performing signed or unsigned fixed-point binary algebra as if the radix point is to the right of b₀.

Within the Fixed-Point Blockset, the main difference between fixed-point data types is the default radix point. For integers and fractionals, the radix point is fixed at the default value. For generalized fixed-point data types, you must either explicitly specify the scaling by configuring dialog box parameters, or inherit the scaling from another block. The supported fixed-point data types are described below.

Integers

The default radix point for signed and unsigned integer data types is assumed to be just to the right of the LSB. You specify unsigned and signed integers with the uint and sint functions, respectively.

Fractionals

The default radix point for unsigned fractional data types is just to the left of the MSB, while for signed fractionals the radix point is just to the right of the MSB. If you specify guard bits, then they lie to the left of the radix point. You specify unsigned and signed fractional numbers with the ufrac and sfrac functions, respectively.

Generalized Fixed-Point Numbers

For signed and unsigned generalized fixed-point numbers, there is no default radix point. You specify unsigned and signed generalized fixed-point numbers with the ufix and sfix functions, respectively.

Signed Fixed-Point Numbers

Scaling