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| bfc108 | 1 | /* ---------------------------------------------------------------------- |
| Q | 2 | * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| 3 | * | |
| 4 | * $Date: 07. September 2015 | |
| 5 | * $Revision: V.1.4.5 a | |
| 6 | * | |
| 7 | * Project: CMSIS DSP Library | |
| 8 | * Title: arm_cos_q15.c | |
| 9 | * | |
| 10 | * Description: Fast cosine calculation for Q15 values. | |
| 11 | * | |
| 12 | * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | |
| 13 | * | |
| 14 | * Redistribution and use in source and binary forms, with or without | |
| 15 | * modification, are permitted provided that the following conditions | |
| 16 | * are met: | |
| 17 | * - Redistributions of source code must retain the above copyright | |
| 18 | * notice, this list of conditions and the following disclaimer. | |
| 19 | * - Redistributions in binary form must reproduce the above copyright | |
| 20 | * notice, this list of conditions and the following disclaimer in | |
| 21 | * the documentation and/or other materials provided with the | |
| 22 | * distribution. | |
| 23 | * - Neither the name of ARM LIMITED nor the names of its contributors | |
| 24 | * may be used to endorse or promote products derived from this | |
| 25 | * software without specific prior written permission. | |
| 26 | * | |
| 27 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
| 28 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
| 29 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS | |
| 30 | * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE | |
| 31 | * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, | |
| 32 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, | |
| 33 | * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; | |
| 34 | * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER | |
| 35 | * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
| 36 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN | |
| 37 | * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE | |
| 38 | * POSSIBILITY OF SUCH DAMAGE. | |
| 39 | * -------------------------------------------------------------------- */ | |
| 40 | ||
| 41 | #include "arm_math.h" | |
| 42 | #include "arm_common_tables.h" | |
| 43 | ||
| 44 | /** | |
| 45 | * @ingroup groupFastMath | |
| 46 | */ | |
| 47 | ||
| 48 | /** | |
| 49 | * @addtogroup cos | |
| 50 | * @{ | |
| 51 | */ | |
| 52 | ||
| 53 | /** | |
| 54 | * @brief Fast approximation to the trigonometric cosine function for Q15 data. | |
| 55 | * @param[in] x Scaled input value in radians. | |
| 56 | * @return cos(x). | |
| 57 | * | |
| 58 | * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian | |
| 59 | * value in the range [0 2*pi). | |
| 60 | */ | |
| 61 | ||
| 62 | q15_t arm_cos_q15( | |
| 63 | q15_t x) | |
| 64 | { | |
| 65 | q15_t cosVal; /* Temporary variables for input, output */ | |
| 66 | int32_t index; /* Index variables */ | |
| 67 | q15_t a, b; /* Four nearest output values */ | |
| 68 | q15_t fract; /* Temporary values for fractional values */ | |
| 69 | ||
| 70 | /* add 0.25 (pi/2) to read sine table */ | |
| 71 | x = (uint16_t)x + 0x2000; | |
| 72 | if(x < 0) | |
| 73 | { /* convert negative numbers to corresponding positive ones */ | |
| 74 | x = (uint16_t)x + 0x8000; | |
| 75 | } | |
| 76 | ||
| 77 | /* Calculate the nearest index */ | |
| 78 | index = (uint32_t)x >> FAST_MATH_Q15_SHIFT; | |
| 79 | ||
| 80 | /* Calculation of fractional value */ | |
| 81 | fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9; | |
| 82 | ||
| 83 | /* Read two nearest values of input value from the sin table */ | |
| 84 | a = sinTable_q15[index]; | |
| 85 | b = sinTable_q15[index+1]; | |
| 86 | ||
| 87 | /* Linear interpolation process */ | |
| 88 | cosVal = (q31_t)(0x8000-fract)*a >> 16; | |
| 89 | cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16); | |
| 90 | ||
| 91 | return cosVal << 1; | |
| 92 | } | |
| 93 | ||
| 94 | /** | |
| 95 | * @} end of cos group | |
| 96 | */ | |
