IQmath Library

IQtoQN
GLOBAL_Q number to QN
Description
This Macro converts a 32-bit number in GLOBAL_Q format to 16-bit
number in QN format.
Declaration int _IQtoQN( _iq A)
Input
Output
IQ number in GLOBAL_Q format
Equivalent value of input in QN format (16-bit fixed point number)
Usage This macro may be used in cases where the input and output data is 16-
bits, but the intermediate operations are operated using IQ data types.
Example:
Sum of product computation using the input sequence that is not in
GLOBAL_Q format:
Y = X0*C0 + X1*C1 + X2*C2
// X0, X1, X2 in Q15 format
// C0, C1, C2 in GLOBAL_Q format
We can convert the Q15 values to IQ, perform the intermediate sums
using IQ and then store the result back as Q15:
short X0, X1, X2;
iq C0, C1, C2;
short Y;
_iq sum
// Q15 short
// GLOBAL_Q
// Q15
// IQ (GLOBAL_Q)
sum = _IQmpy(_Q15toIQ(X0), C0);
sum += _IQmpy(_Q15toIQ(X1), C1);
sum += _IQmpy(_Q15toIQ(X2), C2);
Y = _IQtoQ15(sum);
©Texas Instruments Inc., June 2002 21