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annotate src/inter_6.c @ 8:8b17df8f6340 default tip

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add README
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 17 Apr 2024 17:30:25 +0000
parents 56410792419a
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Interpol_6()
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4 *
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5 * PURPOSE: Interpolating the normalized correlation with 1/6 resolution.
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6 *
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7 *************************************************************************/
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8
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9 #include "typedef.h"
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10 #include "basic_op.h"
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11 #include "count.h"
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12
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13 #define UP_SAMP 6
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14 #define L_INTERPOL 4
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15 #define FIR_SIZE (UP_SAMP*L_INTERPOL+1)
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16
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17 /* 1/6 resolution interpolation filter (-3 dB at 3600 Hz) */
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18
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19 static const Word16 inter_6[FIR_SIZE] =
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20 {
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21 29519,
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22 28316, 24906, 19838, 13896, 7945, 2755,
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23 -1127, -3459, -4304, -3969, -2899, -1561,
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24 -336, 534, 970, 1023, 823, 516,
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25 220, 0, -131, -194, -215, 0
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26 };
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27
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28 Word16 Interpol_6 ( /* (o) : interpolated value */
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29 Word16 *x, /* (i) : input vector */
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30 Word16 frac /* (i) : fraction */
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31 )
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32 {
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33 Word16 i, k;
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34 Word16 *x1, *x2;
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35 const Word16 *c1, *c2;
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36 Word32 s;
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37
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38 test ();
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39 if (frac < 0)
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40 {
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41 frac = add (frac, UP_SAMP);
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42 x--;
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43 }
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44 x1 = &x[0]; move16 ();
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45 x2 = &x[1]; move16 ();
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46 c1 = &inter_6[frac]; move16 ();
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47 c2 = &inter_6[sub (UP_SAMP, frac)]; move16 ();
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48
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49 s = 0; move32 ();
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50 for (i = 0, k = 0; i < L_INTERPOL; i++, k += UP_SAMP)
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51 {
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52 s = L_mac (s, x1[-i], c1[k]);
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53 s = L_mac (s, x2[i], c2[k]);
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54 }
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55
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56 return round (s);
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57 }