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1 /* ----------------------------------------------------------------------
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2 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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3 *
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4 * $Date: 21. September 2015
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5 * $Revision: V.1.4.5 a
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6 *
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7 * Project: CMSIS DSP Library
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8 * Title: arm_cos_f32.c
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9 *
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10 * Description: Fast cosine calculation for floating-point values.
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11 *
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12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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13 *
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14 * Redistribution and use in source and binary forms, with or without
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15 * modification, are permitted provided that the following conditions
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16 * are met:
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17 * - Redistributions of source code must retain the above copyright
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18 * notice, this list of conditions and the following disclaimer.
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19 * - Redistributions in binary form must reproduce the above copyright
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20 * notice, this list of conditions and the following disclaimer in
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21 * the documentation and/or other materials provided with the
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22 * distribution.
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23 * - Neither the name of ARM LIMITED nor the names of its contributors
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24 * may be used to endorse or promote products derived from this
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25 * software without specific prior written permission.
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26 *
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27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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38 * POSSIBILITY OF SUCH DAMAGE.
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39 * -------------------------------------------------------------------- */
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40
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41 #include "arm_math.h"
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42 #include "arm_common_tables.h"
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43 /**
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44 * @ingroup groupFastMath
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45 */
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46
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47 /**
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48 * @defgroup cos Cosine
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49 *
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50 * Computes the trigonometric cosine function using a combination of table lookup
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51 * and linear interpolation. There are separate functions for
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52 * Q15, Q31, and floating-point data types.
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53 * The input to the floating-point version is in radians while the
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54 * fixed-point Q15 and Q31 have a scaled input with the range
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55 * [0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
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56 * value of 2*pi wraps around to 0.
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57 *
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58 * The implementation is based on table lookup using 256 values together with linear interpolation.
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59 * The steps used are:
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60 * -# Calculation of the nearest integer table index
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61 * -# Compute the fractional portion (fract) of the table index.
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62 * -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
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63 *
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64 * where
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65 * <pre>
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66 * b=Table[index+0];
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67 * c=Table[index+1];
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68 * </pre>
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69 */
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70
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71 /**
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72 * @addtogroup cos
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73 * @{
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74 */
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75
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76 /**
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77 * @brief Fast approximation to the trigonometric cosine function for floating-point data.
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78 * @param[in] x input value in radians.
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79 * @return cos(x).
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80 */
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81
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82 float32_t arm_cos_f32(
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83 float32_t x)
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84 {
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85 float32_t cosVal, fract, in; /* Temporary variables for input, output */
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86 uint16_t index; /* Index variable */
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87 float32_t a, b; /* Two nearest output values */
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88 int32_t n;
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89 float32_t findex;
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90
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91 /* input x is in radians */
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92 /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
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93 in = x * 0.159154943092f + 0.25f;
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94
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95 /* Calculation of floor value of input */
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96 n = (int32_t) in;
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97
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98 /* Make negative values towards -infinity */
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99 if(in < 0.0f)
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100 {
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101 n--;
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102 }
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103
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104 /* Map input value to [0 1] */
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105 in = in - (float32_t) n;
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106
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107 /* Calculation of index of the table */
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108 findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
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109 index = ((uint16_t)findex) & 0x1ff;
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110
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111 /* fractional value calculation */
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112 fract = findex - (float32_t) index;
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113
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114 /* Read two nearest values of input value from the cos table */
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115 a = sinTable_f32[index];
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116 b = sinTable_f32[index+1];
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117
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118 /* Linear interpolation process */
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119 cosVal = (1.0f-fract)*a + fract*b;
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120
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121 /* Return the output value */
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122 return (cosVal);
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123 }
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124
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125 /**
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126 * @} end of cos group
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127 */
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