FreeCalypso > hg > gsm-codec-lib
annotate libtwamr/inv_sqrt.h @ 406:85e9768d497f
libtwamr: integrate cl_ltp.c
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 06 May 2024 23:32:59 +0000 |
parents | 54f6bc41ed10 |
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rev | line source |
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libtwamr: integrate a* modules
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1 /* |
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2 ******************************************************************************** |
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3 * |
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4 * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001 |
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5 * R99 Version 3.3.0 |
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6 * REL-4 Version 4.1.0 |
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7 * |
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8 ******************************************************************************** |
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9 * |
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10 * File : inv_sqrt.h |
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11 * Purpose : Computes 1/sqrt(L_x), where L_x is positive. |
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12 * : If L_x is negative or zero, the result is |
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13 * : 1 (3fff ffff). |
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14 * Description : The function 1/sqrt(L_x) is approximated by a table |
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15 * : and linear interpolation. The inverse square root is |
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16 * : computed using the following steps: |
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17 * 1- Normalization of L_x. |
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18 * 2- If (30-exponent) is even then shift right once. |
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19 * 3- exponent = (30-exponent)/2 +1 |
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20 * 4- i = bit25-b31 of L_x; 16<=i<=63 because of normalization. |
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21 * 5- a = bit10-b24 |
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22 * 6- i -=16 |
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23 * 7- L_y = table[i]<<16 - (table[i] - table[i+1]) * a * 2 |
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24 * 8- L_y >>= exponent |
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25 * |
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26 ******************************************************************************** |
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27 */ |
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28 #ifndef inv_sqrt_h |
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29 #define inv_sqrt_h "$Id $" |
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30 |
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31 /* |
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32 ******************************************************************************** |
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33 * INCLUDE FILES |
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34 ******************************************************************************** |
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35 */ |
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36 #include "typedef.h" |
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37 |
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38 /* |
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39 ******************************************************************************** |
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40 * DEFINITION OF DATA TYPES |
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41 ******************************************************************************** |
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42 */ |
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43 |
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44 /* |
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45 ******************************************************************************** |
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46 * DECLARATION OF PROTOTYPES |
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47 ******************************************************************************** |
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48 */ |
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49 |
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50 Word32 Inv_sqrt ( /* (o) : output value (range: 0<=val<1) */ |
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51 Word32 L_x /* (i) : input value (range: 0<=val<=7fffffff) */ |
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52 ); |
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53 |
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54 #endif |