FreeCalypso > hg > gsm-codec-lib
annotate libtwamr/pow2.c @ 479:616b7ba1135b
doc/AMR-library-API: document AMR-EFR hybrid decoder
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sun, 19 May 2024 22:22:40 +0000 |
parents | 190c4c9a3693 |
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libtwamr: integrate pow2.c
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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 : pow2.c |
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11 * Purpose : computes L_x = pow(2.0, exponent.fraction) |
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12 * |
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13 ******************************************************************************** |
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14 */ |
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15 /* |
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16 ******************************************************************************** |
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17 * MODULE INCLUDE FILE AND VERSION ID |
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18 ******************************************************************************** |
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19 */ |
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20 #include "namespace.h" |
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21 #include "pow2.h" |
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22 |
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23 /* |
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24 ******************************************************************************** |
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25 * INCLUDE FILES |
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26 ******************************************************************************** |
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27 */ |
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28 #include "typedef.h" |
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29 #include "basic_op.h" |
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30 #include "no_count.h" |
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31 |
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32 /* |
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33 ******************************************************************************** |
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34 * LOCAL VARIABLES AND TABLES |
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35 ******************************************************************************** |
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36 */ |
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37 #include "pow2.tab" /* Table for Pow2() */ |
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38 |
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39 /* |
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40 ******************************************************************************** |
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41 * PUBLIC PROGRAM CODE |
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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 * FUNCTION: Pow2() |
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47 * |
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48 * PURPOSE: computes L_x = pow(2.0, exponent.fraction) |
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49 * |
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50 * DESCRIPTION: |
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51 * The function Pow2(L_x) is approximated by a table and linear |
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52 * interpolation. |
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53 * 1- i = bit10-b15 of fraction, 0 <= i <= 31 |
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54 * 2- a = bit0-b9 of fraction |
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55 * 3- L_x = table[i]<<16 - (table[i] - table[i+1]) * a * 2 |
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56 * 4- L_x = L_x >> (30-exponent) (with rounding) |
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57 * |
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58 *************************************************************************/ |
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59 Word32 Pow2 ( /* (o) : result (range: 0<=val<=0x7fffffff) */ |
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60 Word16 exponent, /* (i) : Integer part. (range: 0<=val<=30) */ |
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61 Word16 fraction /* (i) : Fractional part. (range: 0.0<=val<1.0) */ |
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62 ) |
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63 { |
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64 Word16 exp, i, a, tmp; |
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65 Word32 L_x; |
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66 |
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67 L_x = L_mult (fraction, 32);/* L_x = fraction<<6 */ |
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68 i = extract_h (L_x); /* Extract b10-b16 of fraction */ |
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69 L_x = L_shr (L_x, 1); |
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70 a = extract_l (L_x); /* Extract b0-b9 of fraction */ |
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71 a = a & (Word16) 0x7fff; logic16 (); |
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72 |
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73 L_x = L_deposit_h (table[i]); /* table[i] << 16 */ |
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74 tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */ |
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75 L_x = L_msu (L_x, tmp, a); /* L_x -= tmp*a*2 */ |
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76 |
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77 exp = sub (30, exponent); |
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78 L_x = L_shr_r (L_x, exp); |
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79 |
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80 return (L_x); |
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81 } |