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Прошу прощения за длинную цитату. Но я не понимаю, как оценивается количество циклов, что такое na и nflags?
acorr Auto-correlation
short oflag = acorr (DATA *x, DATA *r, ushort nx, ushort nr, type)
(defined in araw.asm, abias.asm, aubias.asm)
Arguments: x[nx] Pointer to real input vector of nx real elements. nx >= nr
r[nr] Pointer to real output vector containing the first nr elements of the positive
side of the auto-correlation function of vector a. r must be different than a
(in-place computation is not allowed).
nx Number of real elements in vector x
nr Number of real elements in vector r
type Auto-correlation type selector. Types supported:
· If type = raw, r will contain the raw autocorrelation of x
· If type = bias, r will contain the biased autocorrelation of x
· If type = unbias, r will contain the unbiased autocorrelation of x
oflag Overflow flag
· If oflag = 1 a 32-bit overflow has occurred
· If oflag =0 a 32-bit overflow has not occurred
Description: Computes the first nr points of the positive-side of the auto-correlation of the real
vector x and stores the results are stored in real output vector r. Notice that the
full-length auto-correlation of vector x will have 2*nx-1 points with even symmetry
around the lag 0 point (r[0]). This routine provides only the positive half of this for
memory and computational savings.
Algorithm: Raw Auto-correlation: r[j] = å
- -
=
+
1
0
] [ ] [
j nx
k
k x k j x 0 <=j <=nr
Biased Auto-correlation: r[j] = 1/nx å
- -
=
+
1
0
] [ ] [
j nx
k
k x k j x 0 <=j <=nr
Unbiased Auto-correlation: r[j] = 1/(nx-abs(j)) å
- -
=
+
1
0
] [ ] [
j nx
k
k x k j x 0 <=j <=nr
Overflow Handling Methodology: No scaling implemented for overflow prevention
Special Requirements: None
Implementation Notes:
· Special debugging consideration: This function is implemented as a macro that invokes different
autocorrelation routines according to the type selected. As a consequence the acorr symbol is not
defined. Instead the acorr_raw, acorr_bias, acorr_unbias symbols are defined.
· Autocorrelation is implemented using time-domain techniques.
Example: See examples/abias, examples/aubias, examples/araw subdirectories.
SPRA480B
14 Optimized DSP Library for C Programmers on the TMS320C54x
Benchmarks:
Cycles Abias
Core:
((na-1) * (na-2)) + ((nlags) * 13) + 26
Overhead 68
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