FreeCalypso > hg > gsm-codec-lib
annotate libtwamr/log2.c @ 486:f35c8fd9ceba
CHANGES: document gsmrec-dump improvements
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 20 May 2024 02:07:30 +0000 |
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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 : log2.c |
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11 * Purpose : Computes log2(L_x) |
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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 "log2.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 "log2.tab" /* Table for Log2() */ |
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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 * |
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47 * FUNCTION: Log2_norm() |
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48 * |
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49 * PURPOSE: Computes log2(L_x, exp), where L_x is positive and |
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50 * normalized, and exp is the normalisation exponent |
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51 * If L_x is negative or zero, the result is 0. |
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52 * |
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53 * DESCRIPTION: |
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54 * The function Log2(L_x) is approximated by a table and linear |
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55 * interpolation. The following steps are used to compute Log2(L_x) |
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56 * |
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57 * 1- exponent = 30-norm_exponent |
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58 * 2- i = bit25-b31 of L_x; 32<=i<=63 (because of normalization). |
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59 * 3- a = bit10-b24 |
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60 * 4- i -=32 |
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61 * 5- fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 |
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62 * |
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63 *************************************************************************/ |
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64 void Log2_norm ( |
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65 Word32 L_x, /* (i) : input value (normalized) */ |
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66 Word16 exp, /* (i) : norm_l (L_x) */ |
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67 Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30) */ |
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68 Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ |
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69 ) |
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70 { |
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71 Word16 i, a, tmp; |
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72 Word32 L_y; |
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73 |
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74 test (); |
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75 if (L_x <= (Word32) 0) |
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76 { |
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77 *exponent = 0; move16 (); |
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78 *fraction = 0; move16 (); |
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79 return; |
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80 } |
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81 |
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82 *exponent = sub (30, exp); move16 (); |
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83 |
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84 L_x = L_shr (L_x, 9); |
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85 i = extract_h (L_x); /* Extract b25-b31 */ |
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86 L_x = L_shr (L_x, 1); |
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87 a = extract_l (L_x); /* Extract b10-b24 of fraction */ |
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88 a = a & (Word16) 0x7fff; logic16 (); |
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89 |
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90 i = sub (i, 32); |
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91 |
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92 L_y = L_deposit_h (table[i]); /* table[i] << 16 */ |
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93 tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */ |
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94 L_y = L_msu (L_y, tmp, a); /* L_y -= tmp*a*2 */ |
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95 |
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96 *fraction = extract_h (L_y);move16 (); |
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97 |
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98 return; |
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99 } |
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100 |
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101 /************************************************************************* |
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102 * |
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103 * FUNCTION: Log2() |
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104 * |
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105 * PURPOSE: Computes log2(L_x), where L_x is positive. |
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106 * If L_x is negative or zero, the result is 0. |
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107 * |
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108 * DESCRIPTION: |
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109 * normalizes L_x and then calls Log2_norm(). |
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110 * |
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111 *************************************************************************/ |
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112 void Log2 ( |
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113 Word32 L_x, /* (i) : input value */ |
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114 Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30) */ |
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115 Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ |
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116 ) |
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117 { |
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118 Word16 exp; |
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119 |
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120 exp = norm_l (L_x); |
bfe74a9edd5a
libtwamr: integrate log2.c
Mychaela Falconia <falcon@freecalypso.org>
parents:
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121 Log2_norm (L_shl (L_x, exp), exp, exponent, fraction); |
bfe74a9edd5a
libtwamr: integrate log2.c
Mychaela Falconia <falcon@freecalypso.org>
parents:
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122 } |