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annotate libtwamr/inv_sqrt.h @ 256:a33edf624061

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libgsmfr2: start with API definition and port of libgsmfrp code
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 12 Apr 2024 20:49:53 +0000
parents 54f6bc41ed10
children
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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