Fixed-Point Operations :: Using Fixed-Point Data in Stateflow (Stateflow User's Guide)

Stateflow User's Guide

Fixed-Point Operations

Now that you can express fixed-point numbers as , you can define operations between two fixed-point numbers.

The general equation for an operation between fixed-point operands is as follows:

c = a <op> b

where a, b, and c are all fixed-point numbers, and <op> refers to one of the binary operations: addition, subtraction, multiplication, or division.

The general form for a fixed-point number x is (see Fixed-Point Numbers). Substituting this form for the result and operands in the preceding equation yields the following:

The values for and are usually chosen by Stateflow for each operation (see Promotion Rules for Fixed-Point Operations) and are based on the values for , , , and , which are entered for each fixed-point data (see Specifying Fixed-Point Data in Stateflow).

Note Stateflow also offers a more precise means for choosing the values for

and

when you use the := assignment operator (that is, c := a <op> b). See Assignment (=, :=) Operations for more detail.

Using the values for , and , you can solve the preceding equation for for each binary operation as follows:

The operation c=a+b implies that
The operation c=a-b implies that
The operation c=a*b implies that
The operation c=a/b implies that

The fixed-point approximations of the real number result of the operation c = a <op> b are given by the preceding solutions for the value . In this way, all fixed-point operations are performed using only the stored integer for each fixed-point number and integer operation.

Fixed-Point Numbers Using Fixed-Point Data in Stateflow