mbed official / mbed-dsp

CMSIS DSP library

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cmsis_dsp/FastMathFunctions/arm_cos_f32.c@3:7a284390b0ce, 2013-11-08 (annotated)

Committer:
mbed_official
Date:
Fri Nov 08 13:45:10 2013 +0000
Revision:
3:7a284390b0ce
Parent:
2:da51fb522205 
Synchronized with git revision e69956aba2f68a2a26ac26b051f8d349deaa1ce8

Who changed what in which revision?

UserRevisionLine numberNew contents of line
emilmont 1:fdd22bb7aa52 1 /* ----------------------------------------------------------------------
mbed_official 3:7a284390b0ce 2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
emilmont 1:fdd22bb7aa52 3 *
mbed_official 3:7a284390b0ce 4 * $Date: 17. January 2013
mbed_official 3:7a284390b0ce 5 * $Revision: V1.4.1
emilmont 1:fdd22bb7aa52 6 *
emilmont 2:da51fb522205 7 * Project: CMSIS DSP Library
emilmont 2:da51fb522205 8 * Title: arm_cos_f32.c
emilmont 1:fdd22bb7aa52 9 *
emilmont 2:da51fb522205 10 * Description: Fast cosine calculation for floating-point values.
emilmont 1:fdd22bb7aa52 11 *
emilmont 1:fdd22bb7aa52 12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
emilmont 1:fdd22bb7aa52 13 *
mbed_official 3:7a284390b0ce 14 * Redistribution and use in source and binary forms, with or without
mbed_official 3:7a284390b0ce 15 * modification, are permitted provided that the following conditions
mbed_official 3:7a284390b0ce 16 * are met:
mbed_official 3:7a284390b0ce 17 * - Redistributions of source code must retain the above copyright
mbed_official 3:7a284390b0ce 18 * notice, this list of conditions and the following disclaimer.
mbed_official 3:7a284390b0ce 19 * - Redistributions in binary form must reproduce the above copyright
mbed_official 3:7a284390b0ce 20 * notice, this list of conditions and the following disclaimer in
mbed_official 3:7a284390b0ce 21 * the documentation and/or other materials provided with the
mbed_official 3:7a284390b0ce 22 * distribution.
mbed_official 3:7a284390b0ce 23 * - Neither the name of ARM LIMITED nor the names of its contributors
mbed_official 3:7a284390b0ce 24 * may be used to endorse or promote products derived from this
mbed_official 3:7a284390b0ce 25 * software without specific prior written permission.
mbed_official 3:7a284390b0ce 26 *
mbed_official 3:7a284390b0ce 27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
mbed_official 3:7a284390b0ce 28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
mbed_official 3:7a284390b0ce 29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
mbed_official 3:7a284390b0ce 30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
mbed_official 3:7a284390b0ce 31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
mbed_official 3:7a284390b0ce 32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
mbed_official 3:7a284390b0ce 33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
mbed_official 3:7a284390b0ce 34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
mbed_official 3:7a284390b0ce 35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
mbed_official 3:7a284390b0ce 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
mbed_official 3:7a284390b0ce 37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
mbed_official 3:7a284390b0ce 38 * POSSIBILITY OF SUCH DAMAGE.
emilmont 1:fdd22bb7aa52 39 * -------------------------------------------------------------------- */
emilmont 1:fdd22bb7aa52 40
emilmont 1:fdd22bb7aa52 41 #include "arm_math.h"
emilmont 1:fdd22bb7aa52 42 /**
emilmont 1:fdd22bb7aa52 43 * @ingroup groupFastMath
emilmont 1:fdd22bb7aa52 44 */
emilmont 1:fdd22bb7aa52 45
emilmont 1:fdd22bb7aa52 46 /**
emilmont 1:fdd22bb7aa52 47 * @defgroup cos Cosine
emilmont 1:fdd22bb7aa52 48 *
emilmont 1:fdd22bb7aa52 49 * Computes the trigonometric cosine function using a combination of table lookup
emilmont 1:fdd22bb7aa52 50 * and cubic interpolation. There are separate functions for
emilmont 1:fdd22bb7aa52 51 * Q15, Q31, and floating-point data types.
emilmont 1:fdd22bb7aa52 52 * The input to the floating-point version is in radians while the
emilmont 1:fdd22bb7aa52 53 * fixed-point Q15 and Q31 have a scaled input with the range
mbed_official 3:7a284390b0ce 54 * [0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
mbed_official 3:7a284390b0ce 55 * value of 2*pi wraps around to 0.
emilmont 1:fdd22bb7aa52 56 *
emilmont 1:fdd22bb7aa52 57 * The implementation is based on table lookup using 256 values together with cubic interpolation.
emilmont 1:fdd22bb7aa52 58 * The steps used are:
emilmont 1:fdd22bb7aa52 59 * -# Calculation of the nearest integer table index
emilmont 1:fdd22bb7aa52 60 * -# Fetch the four table values a, b, c, and d
emilmont 1:fdd22bb7aa52 61 * -# Compute the fractional portion (fract) of the table index.
emilmont 1:fdd22bb7aa52 62 * -# Calculation of wa, wb, wc, wd
emilmont 1:fdd22bb7aa52 63 * -# The final result equals <code>a*wa + b*wb + c*wc + d*wd</code>
emilmont 1:fdd22bb7aa52 64 *
emilmont 1:fdd22bb7aa52 65 * where
emilmont 1:fdd22bb7aa52 66 * <pre>
emilmont 1:fdd22bb7aa52 67 * a=Table[index-1];
emilmont 1:fdd22bb7aa52 68 * b=Table[index+0];
emilmont 1:fdd22bb7aa52 69 * c=Table[index+1];
emilmont 1:fdd22bb7aa52 70 * d=Table[index+2];
emilmont 1:fdd22bb7aa52 71 * </pre>
emilmont 1:fdd22bb7aa52 72 * and
emilmont 1:fdd22bb7aa52 73 * <pre>
emilmont 1:fdd22bb7aa52 74 * wa=-(1/6)*fract.^3 + (1/2)*fract.^2 - (1/3)*fract;
emilmont 1:fdd22bb7aa52 75 * wb=(1/2)*fract.^3 - fract.^2 - (1/2)*fract + 1;
emilmont 1:fdd22bb7aa52 76 * wc=-(1/2)*fract.^3+(1/2)*fract.^2+fract;
emilmont 1:fdd22bb7aa52 77 * wd=(1/6)*fract.^3 - (1/6)*fract;
emilmont 1:fdd22bb7aa52 78 * </pre>
emilmont 1:fdd22bb7aa52 79 */
emilmont 1:fdd22bb7aa52 80
emilmont 1:fdd22bb7aa52 81 /**
emilmont 1:fdd22bb7aa52 82 * @addtogroup cos
emilmont 1:fdd22bb7aa52 83 * @{
emilmont 1:fdd22bb7aa52 84 */
emilmont 1:fdd22bb7aa52 85
emilmont 1:fdd22bb7aa52 86
emilmont 1:fdd22bb7aa52 87 /**
emilmont 1:fdd22bb7aa52 88 * \par
mbed_official 3:7a284390b0ce 89 * <b>Example code for Generation of Cos Table:</b>
mbed_official 3:7a284390b0ce 90 * <pre>
emilmont 1:fdd22bb7aa52 91 * tableSize = 256;
mbed_official 3:7a284390b0ce 92 * for(n = -1; n < (tableSize + 2); n++)
emilmont 1:fdd22bb7aa52 93 * {
emilmont 2:da51fb522205 94 * cosTable[n+1]= cos(2*pi*n/tableSize);
emilmont 1:fdd22bb7aa52 95 * } </pre>
emilmont 1:fdd22bb7aa52 96 * where pi value is 3.14159265358979
emilmont 1:fdd22bb7aa52 97 */
emilmont 1:fdd22bb7aa52 98
emilmont 1:fdd22bb7aa52 99 static const float32_t cosTable[260] = {
emilmont 1:fdd22bb7aa52 100 0.999698817729949950f, 1.000000000000000000f, 0.999698817729949950f,
emilmont 1:fdd22bb7aa52 101 0.998795449733734130f, 0.997290432453155520f, 0.995184719562530520f,
emilmont 1:fdd22bb7aa52 102 0.992479562759399410f, 0.989176511764526370f,
emilmont 1:fdd22bb7aa52 103 0.985277652740478520f, 0.980785250663757320f, 0.975702106952667240f,
emilmont 1:fdd22bb7aa52 104 0.970031261444091800f, 0.963776051998138430f, 0.956940352916717530f,
emilmont 1:fdd22bb7aa52 105 0.949528157711029050f, 0.941544055938720700f,
emilmont 1:fdd22bb7aa52 106 0.932992815971374510f, 0.923879504203796390f, 0.914209783077239990f,
emilmont 1:fdd22bb7aa52 107 0.903989315032958980f, 0.893224298954010010f, 0.881921291351318360f,
emilmont 1:fdd22bb7aa52 108 0.870086967945098880f, 0.857728600502014160f,
emilmont 1:fdd22bb7aa52 109 0.844853579998016360f, 0.831469595432281490f, 0.817584812641143800f,
emilmont 1:fdd22bb7aa52 110 0.803207516670227050f, 0.788346409797668460f, 0.773010432720184330f,
emilmont 1:fdd22bb7aa52 111 0.757208824157714840f, 0.740951120853424070f,
emilmont 1:fdd22bb7aa52 112 0.724247097969055180f, 0.707106769084930420f, 0.689540565013885500f,
emilmont 1:fdd22bb7aa52 113 0.671558976173400880f, 0.653172850608825680f, 0.634393274784088130f,
emilmont 1:fdd22bb7aa52 114 0.615231573581695560f, 0.595699310302734380f,
emilmont 1:fdd22bb7aa52 115 0.575808167457580570f, 0.555570244789123540f, 0.534997642040252690f,
emilmont 1:fdd22bb7aa52 116 0.514102756977081300f, 0.492898195981979370f, 0.471396744251251220f,
emilmont 1:fdd22bb7aa52 117 0.449611335992813110f, 0.427555084228515630f,
emilmont 1:fdd22bb7aa52 118 0.405241310596466060f, 0.382683426141738890f, 0.359895050525665280f,
emilmont 1:fdd22bb7aa52 119 0.336889863014221190f, 0.313681751489639280f, 0.290284663438797000f,
emilmont 1:fdd22bb7aa52 120 0.266712754964828490f, 0.242980182170867920f,
emilmont 1:fdd22bb7aa52 121 0.219101235270500180f, 0.195090323686599730f, 0.170961886644363400f,
emilmont 1:fdd22bb7aa52 122 0.146730467677116390f, 0.122410677373409270f, 0.098017141222953796f,
emilmont 1:fdd22bb7aa52 123 0.073564566671848297f, 0.049067676067352295f,
emilmont 1:fdd22bb7aa52 124 0.024541229009628296f, 0.000000000000000061f, -0.024541229009628296f,
emilmont 1:fdd22bb7aa52 125 -0.049067676067352295f, -0.073564566671848297f, -0.098017141222953796f,
emilmont 1:fdd22bb7aa52 126 -0.122410677373409270f, -0.146730467677116390f,
emilmont 1:fdd22bb7aa52 127 -0.170961886644363400f, -0.195090323686599730f, -0.219101235270500180f,
emilmont 1:fdd22bb7aa52 128 -0.242980182170867920f, -0.266712754964828490f, -0.290284663438797000f,
emilmont 1:fdd22bb7aa52 129 -0.313681751489639280f, -0.336889863014221190f,
emilmont 1:fdd22bb7aa52 130 -0.359895050525665280f, -0.382683426141738890f, -0.405241310596466060f,
emilmont 1:fdd22bb7aa52 131 -0.427555084228515630f, -0.449611335992813110f, -0.471396744251251220f,
emilmont 1:fdd22bb7aa52 132 -0.492898195981979370f, -0.514102756977081300f,
emilmont 1:fdd22bb7aa52 133 -0.534997642040252690f, -0.555570244789123540f, -0.575808167457580570f,
emilmont 1:fdd22bb7aa52 134 -0.595699310302734380f, -0.615231573581695560f, -0.634393274784088130f,
emilmont 1:fdd22bb7aa52 135 -0.653172850608825680f, -0.671558976173400880f,
emilmont 1:fdd22bb7aa52 136 -0.689540565013885500f, -0.707106769084930420f, -0.724247097969055180f,
emilmont 1:fdd22bb7aa52 137 -0.740951120853424070f, -0.757208824157714840f, -0.773010432720184330f,
emilmont 1:fdd22bb7aa52 138 -0.788346409797668460f, -0.803207516670227050f,
emilmont 1:fdd22bb7aa52 139 -0.817584812641143800f, -0.831469595432281490f, -0.844853579998016360f,
emilmont 1:fdd22bb7aa52 140 -0.857728600502014160f, -0.870086967945098880f, -0.881921291351318360f,
emilmont 1:fdd22bb7aa52 141 -0.893224298954010010f, -0.903989315032958980f,
emilmont 1:fdd22bb7aa52 142 -0.914209783077239990f, -0.923879504203796390f, -0.932992815971374510f,
emilmont 1:fdd22bb7aa52 143 -0.941544055938720700f, -0.949528157711029050f, -0.956940352916717530f,
emilmont 1:fdd22bb7aa52 144 -0.963776051998138430f, -0.970031261444091800f,
emilmont 1:fdd22bb7aa52 145 -0.975702106952667240f, -0.980785250663757320f, -0.985277652740478520f,
emilmont 1:fdd22bb7aa52 146 -0.989176511764526370f, -0.992479562759399410f, -0.995184719562530520f,
emilmont 1:fdd22bb7aa52 147 -0.997290432453155520f, -0.998795449733734130f,
emilmont 1:fdd22bb7aa52 148 -0.999698817729949950f, -1.000000000000000000f, -0.999698817729949950f,
emilmont 1:fdd22bb7aa52 149 -0.998795449733734130f, -0.997290432453155520f, -0.995184719562530520f,
emilmont 1:fdd22bb7aa52 150 -0.992479562759399410f, -0.989176511764526370f,
emilmont 1:fdd22bb7aa52 151 -0.985277652740478520f, -0.980785250663757320f, -0.975702106952667240f,
emilmont 1:fdd22bb7aa52 152 -0.970031261444091800f, -0.963776051998138430f, -0.956940352916717530f,
emilmont 1:fdd22bb7aa52 153 -0.949528157711029050f, -0.941544055938720700f,
emilmont 1:fdd22bb7aa52 154 -0.932992815971374510f, -0.923879504203796390f, -0.914209783077239990f,
emilmont 1:fdd22bb7aa52 155 -0.903989315032958980f, -0.893224298954010010f, -0.881921291351318360f,
emilmont 1:fdd22bb7aa52 156 -0.870086967945098880f, -0.857728600502014160f,
emilmont 1:fdd22bb7aa52 157 -0.844853579998016360f, -0.831469595432281490f, -0.817584812641143800f,
emilmont 1:fdd22bb7aa52 158 -0.803207516670227050f, -0.788346409797668460f, -0.773010432720184330f,
emilmont 1:fdd22bb7aa52 159 -0.757208824157714840f, -0.740951120853424070f,
emilmont 1:fdd22bb7aa52 160 -0.724247097969055180f, -0.707106769084930420f, -0.689540565013885500f,
emilmont 1:fdd22bb7aa52 161 -0.671558976173400880f, -0.653172850608825680f, -0.634393274784088130f,
emilmont 1:fdd22bb7aa52 162 -0.615231573581695560f, -0.595699310302734380f,
emilmont 1:fdd22bb7aa52 163 -0.575808167457580570f, -0.555570244789123540f, -0.534997642040252690f,
emilmont 1:fdd22bb7aa52 164 -0.514102756977081300f, -0.492898195981979370f, -0.471396744251251220f,
emilmont 1:fdd22bb7aa52 165 -0.449611335992813110f, -0.427555084228515630f,
emilmont 1:fdd22bb7aa52 166 -0.405241310596466060f, -0.382683426141738890f, -0.359895050525665280f,
emilmont 1:fdd22bb7aa52 167 -0.336889863014221190f, -0.313681751489639280f, -0.290284663438797000f,
emilmont 1:fdd22bb7aa52 168 -0.266712754964828490f, -0.242980182170867920f,
emilmont 1:fdd22bb7aa52 169 -0.219101235270500180f, -0.195090323686599730f, -0.170961886644363400f,
emilmont 1:fdd22bb7aa52 170 -0.146730467677116390f, -0.122410677373409270f, -0.098017141222953796f,
emilmont 1:fdd22bb7aa52 171 -0.073564566671848297f, -0.049067676067352295f,
emilmont 1:fdd22bb7aa52 172 -0.024541229009628296f, -0.000000000000000184f, 0.024541229009628296f,
emilmont 1:fdd22bb7aa52 173 0.049067676067352295f, 0.073564566671848297f, 0.098017141222953796f,
emilmont 1:fdd22bb7aa52 174 0.122410677373409270f, 0.146730467677116390f,
emilmont 1:fdd22bb7aa52 175 0.170961886644363400f, 0.195090323686599730f, 0.219101235270500180f,
emilmont 1:fdd22bb7aa52 176 0.242980182170867920f, 0.266712754964828490f, 0.290284663438797000f,
emilmont 1:fdd22bb7aa52 177 0.313681751489639280f, 0.336889863014221190f,
emilmont 1:fdd22bb7aa52 178 0.359895050525665280f, 0.382683426141738890f, 0.405241310596466060f,
emilmont 1:fdd22bb7aa52 179 0.427555084228515630f, 0.449611335992813110f, 0.471396744251251220f,
emilmont 1:fdd22bb7aa52 180 0.492898195981979370f, 0.514102756977081300f,
emilmont 1:fdd22bb7aa52 181 0.534997642040252690f, 0.555570244789123540f, 0.575808167457580570f,
emilmont 1:fdd22bb7aa52 182 0.595699310302734380f, 0.615231573581695560f, 0.634393274784088130f,
emilmont 1:fdd22bb7aa52 183 0.653172850608825680f, 0.671558976173400880f,
emilmont 1:fdd22bb7aa52 184 0.689540565013885500f, 0.707106769084930420f, 0.724247097969055180f,
emilmont 1:fdd22bb7aa52 185 0.740951120853424070f, 0.757208824157714840f, 0.773010432720184330f,
emilmont 1:fdd22bb7aa52 186 0.788346409797668460f, 0.803207516670227050f,
emilmont 1:fdd22bb7aa52 187 0.817584812641143800f, 0.831469595432281490f, 0.844853579998016360f,
emilmont 1:fdd22bb7aa52 188 0.857728600502014160f, 0.870086967945098880f, 0.881921291351318360f,
emilmont 1:fdd22bb7aa52 189 0.893224298954010010f, 0.903989315032958980f,
emilmont 1:fdd22bb7aa52 190 0.914209783077239990f, 0.923879504203796390f, 0.932992815971374510f,
emilmont 1:fdd22bb7aa52 191 0.941544055938720700f, 0.949528157711029050f, 0.956940352916717530f,
emilmont 1:fdd22bb7aa52 192 0.963776051998138430f, 0.970031261444091800f,
emilmont 1:fdd22bb7aa52 193 0.975702106952667240f, 0.980785250663757320f, 0.985277652740478520f,
emilmont 1:fdd22bb7aa52 194 0.989176511764526370f, 0.992479562759399410f, 0.995184719562530520f,
emilmont 1:fdd22bb7aa52 195 0.997290432453155520f, 0.998795449733734130f,
emilmont 1:fdd22bb7aa52 196 0.999698817729949950f, 1.000000000000000000f, 0.999698817729949950f,
emilmont 1:fdd22bb7aa52 197 0.998795449733734130f
emilmont 1:fdd22bb7aa52 198 };
emilmont 1:fdd22bb7aa52 199
emilmont 1:fdd22bb7aa52 200 /**
emilmont 1:fdd22bb7aa52 201 * @brief Fast approximation to the trigonometric cosine function for floating-point data.
emilmont 1:fdd22bb7aa52 202 * @param[in] x input value in radians.
emilmont 1:fdd22bb7aa52 203 * @return cos(x).
emilmont 1:fdd22bb7aa52 204 */
emilmont 1:fdd22bb7aa52 205
emilmont 1:fdd22bb7aa52 206
emilmont 1:fdd22bb7aa52 207 float32_t arm_cos_f32(
emilmont 1:fdd22bb7aa52 208 float32_t x)
emilmont 1:fdd22bb7aa52 209 {
emilmont 1:fdd22bb7aa52 210 float32_t cosVal, fract, in;
emilmont 1:fdd22bb7aa52 211 int32_t index;
emilmont 1:fdd22bb7aa52 212 uint32_t tableSize = (uint32_t) TABLE_SIZE;
emilmont 1:fdd22bb7aa52 213 float32_t wa, wb, wc, wd;
emilmont 1:fdd22bb7aa52 214 float32_t a, b, c, d;
emilmont 1:fdd22bb7aa52 215 float32_t *tablePtr;
emilmont 1:fdd22bb7aa52 216 int32_t n;
emilmont 1:fdd22bb7aa52 217 float32_t fractsq, fractby2, fractby6, fractby3, fractsqby2;
emilmont 1:fdd22bb7aa52 218 float32_t oneminusfractby2;
emilmont 1:fdd22bb7aa52 219 float32_t frby2xfrsq, frby6xfrsq;
emilmont 1:fdd22bb7aa52 220
emilmont 1:fdd22bb7aa52 221 /* input x is in radians */
emilmont 1:fdd22bb7aa52 222 /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi */
emilmont 1:fdd22bb7aa52 223 in = x * 0.159154943092f;
emilmont 1:fdd22bb7aa52 224
emilmont 1:fdd22bb7aa52 225 /* Calculation of floor value of input */
emilmont 1:fdd22bb7aa52 226 n = (int32_t) in;
emilmont 1:fdd22bb7aa52 227
emilmont 1:fdd22bb7aa52 228 /* Make negative values towards -infinity */
emilmont 1:fdd22bb7aa52 229 if(x < 0.0f)
emilmont 1:fdd22bb7aa52 230 {
emilmont 1:fdd22bb7aa52 231 n = n - 1;
emilmont 1:fdd22bb7aa52 232 }
emilmont 1:fdd22bb7aa52 233
emilmont 1:fdd22bb7aa52 234 /* Map input value to [0 1] */
emilmont 1:fdd22bb7aa52 235 in = in - (float32_t) n;
emilmont 1:fdd22bb7aa52 236
emilmont 1:fdd22bb7aa52 237 /* Calculation of index of the table */
emilmont 1:fdd22bb7aa52 238 index = (uint32_t) (tableSize * in);
emilmont 1:fdd22bb7aa52 239
emilmont 1:fdd22bb7aa52 240 /* fractional value calculation */
emilmont 1:fdd22bb7aa52 241 fract = ((float32_t) tableSize * in) - (float32_t) index;
emilmont 1:fdd22bb7aa52 242
emilmont 1:fdd22bb7aa52 243 /* Checking min and max index of table */
emilmont 1:fdd22bb7aa52 244 if(index < 0)
emilmont 1:fdd22bb7aa52 245 {
emilmont 1:fdd22bb7aa52 246 index = 0;
emilmont 1:fdd22bb7aa52 247 }
emilmont 1:fdd22bb7aa52 248 else if(index > 256)
emilmont 1:fdd22bb7aa52 249 {
emilmont 1:fdd22bb7aa52 250 index = 256;
emilmont 1:fdd22bb7aa52 251 }
emilmont 1:fdd22bb7aa52 252
emilmont 1:fdd22bb7aa52 253 /* Initialise table pointer */
emilmont 1:fdd22bb7aa52 254 tablePtr = (float32_t *) & cosTable[index];
emilmont 1:fdd22bb7aa52 255
emilmont 1:fdd22bb7aa52 256 /* Read four nearest values of input value from the cos table */
emilmont 1:fdd22bb7aa52 257 a = tablePtr[0];
emilmont 1:fdd22bb7aa52 258 b = tablePtr[1];
emilmont 1:fdd22bb7aa52 259 c = tablePtr[2];
emilmont 1:fdd22bb7aa52 260 d = tablePtr[3];
emilmont 1:fdd22bb7aa52 261
emilmont 1:fdd22bb7aa52 262 /* Cubic interpolation process */
emilmont 1:fdd22bb7aa52 263 fractsq = fract * fract;
emilmont 1:fdd22bb7aa52 264 fractby2 = fract * 0.5f;
emilmont 1:fdd22bb7aa52 265 fractby6 = fract * 0.166666667f;
emilmont 1:fdd22bb7aa52 266 fractby3 = fract * 0.3333333333333f;
emilmont 1:fdd22bb7aa52 267 fractsqby2 = fractsq * 0.5f;
emilmont 1:fdd22bb7aa52 268 frby2xfrsq = (fractby2) * fractsq;
emilmont 1:fdd22bb7aa52 269 frby6xfrsq = (fractby6) * fractsq;
emilmont 1:fdd22bb7aa52 270 oneminusfractby2 = 1.0f - fractby2;
emilmont 1:fdd22bb7aa52 271 wb = fractsqby2 - fractby3;
emilmont 1:fdd22bb7aa52 272 wc = (fractsqby2 + fract);
emilmont 1:fdd22bb7aa52 273 wa = wb - frby6xfrsq;
emilmont 1:fdd22bb7aa52 274 wb = frby2xfrsq - fractsq;
emilmont 1:fdd22bb7aa52 275 cosVal = wa * a;
emilmont 1:fdd22bb7aa52 276 wc = wc - frby2xfrsq;
emilmont 1:fdd22bb7aa52 277 wd = (frby6xfrsq) - fractby6;
emilmont 1:fdd22bb7aa52 278 wb = wb + oneminusfractby2;
emilmont 1:fdd22bb7aa52 279
emilmont 1:fdd22bb7aa52 280 /* Calculate cos value */
emilmont 1:fdd22bb7aa52 281 cosVal = (cosVal + (b * wb)) + ((c * wc) + (d * wd));
emilmont 1:fdd22bb7aa52 282
emilmont 1:fdd22bb7aa52 283 /* Return the output value */
emilmont 1:fdd22bb7aa52 284 return (cosVal);
emilmont 1:fdd22bb7aa52 285
emilmont 1:fdd22bb7aa52 286 }
emilmont 1:fdd22bb7aa52 287
emilmont 1:fdd22bb7aa52 288 /**
emilmont 1:fdd22bb7aa52 289 * @} end of cos group
emilmont 1:fdd22bb7aa52 290 */