IQmath Library

IQtoIQN
GLOBAL_Q number to IQN
Description
This Macro converts an IQ number in GLOBAL_Q format to the specified
IQ format.
Declaration _iqN _IQtoIQN( _iq A)
Input
Output
IQ number in GLOBAL_Q format
Equivalent value of input in IQN format
Usage
This macro may be used in cases where a calculation may temporarily
overflow the IQ value resolution and hence require a different IQ value to
be used for the intermediate operations.
Example:
Following example calculates the magnitude of complex number (X+jY)
in Q26 format:
Z = sqrt(X^2 + Y^2)
The values Z, X, Y are given as GLOBAL_Q = 26, but the equation itself
may generate an overflow.
To guard against this, the intermediate calculations will be performed
using Q = 23 and the value converted back at the end as shown below:
_iq Z, Y, X; // GLOBAL_Q = 26
_iq23 temp;
temp = _IQ23sqrt( _IQ23mpy(_IQtoIQ23(X), _IQtoIQ23(X)) +
_IQ23mpy(_IQtoIQ23(Y), _IQtoIQ23(Y)) );
Y = _IQ23toIQ(temp);
©Texas Instruments Inc., June 2002 19