Texas Instruments TMS320C64X User Manual
Page 32
DSP_autocor
4-4
4.2
Correlation
AutoCorrelation
DSP_autocor
Function
void DSP_autocor(short * restrict r, const short * restrict x, int nx, int nr)
Arguments
r[nr]
Output array
x[nx+nr]
Input array. Must be double-word aligned.
nx
Length of autocorrelation. Must be a multiple of 8.
nr
Number of lags. Must be a multiple of 4.
Description
This routine accepts an input array of length nx + nr and performs nr
autocorrelations each of length nx producing nr output results. This is typically
used in VSELP code.
Algorithm
This is the C equivalent of the assembly code without restrictions. Note that
the assembly code is hand optimized and restrictions may apply.
void DSP_autocor(short r[ ],short x[ ], int nx, int nr)
{
int i,k,sum;
for (i = 0; i < nr; i++){
sum = 0;
for (k = nr; k < nx+nr; k++)
sum += x[k] * x[k−i];
r[i] = (sum >> 15);
}
}
Special Requirements
-
nx must be a multiple of 8.
-
nr must be a multiple of 4.
-
x[ ] must be double-word aligned.