To Next Page

To Previous Page

IQmath

8 - 20 C2000 Microcontroller Workshop - Numerical Concepts

Using the operator overloading features of C++, we can overload the multiplication operand "*"

such that when a particular data type is encountered, it will automatically implement the scaled

multiply operation. Let’s define a data type called "iq" and assign the linear variables to this data

type:

iq Y, M, X, B // numbers are all Q24

The overloading of the multiply operand in C++ can be defined as follows:

iq operator*(const iq &M, const iq &X){return((int64)M*(int64) X) >> 24;}

Then the linear equation, in C++, becomes:

Y = M * X + B;

This final equation looks identical to the floating-point representation. It looks "natural". The

four approaches are summarized in the table below:

Math Implementations

Linear Equation Code

32-bit floating-point math in C

Y = M * X + B;

32-bit fixed-point "Q" math in C

Y = ((int64) M * (int64) X) + (int64) B << 24) >> 24;

32-bit IQmath in C

Y = _IQ24mpy(M, X) + B;

32-bit IQmath in C++

Y = M * X + B;

Essentially, the mathematical approach of scaling the multiplier operand enables a cleaner and a

more "natural" approach to coding fixed-point problems. For want of a better term, we call this

approach "IQmath" or can also be described as "virtual floating-point".

Texas Instruments C2000 Workshop Guide And Lab Manual

Other manuals for Texas Instruments C2000