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DSP_autocor_rA8
4-6
AutoCorrelation
DSP_autocor_rA8
Function void DSP_autocor_rA8(short * restrict r, const short * restrict x, int nx, int nr)
Arguments r[nr] Output array, Must be double word aligned.
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.
- r[ ] must be double-word aligned.
Implementation Notes
- Bank Conflicts: No bank conflicts occur.
- Interruptibility: The code is interruptible.
- The inner loop is unrolled 8 times.
- The outer loop is unrolled 4 times.