| 1 | /* ----------------------------------------------------------------------
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| 2 | * Project: CMSIS DSP Library
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| 3 | * Title: arm_cos_q15.c
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| 4 | * Description: Fast cosine calculation for Q15 values
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| 5 | *
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| 6 | * $Date: 27. January 2017
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| 7 | * $Revision: V.1.5.1
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| 8 | *
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| 9 | * Target Processor: Cortex-M cores
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| 10 | * -------------------------------------------------------------------- */
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| 11 | /*
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| 12 | * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
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| 13 | *
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| 14 | * SPDX-License-Identifier: Apache-2.0
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| 15 | *
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| 16 | * Licensed under the Apache License, Version 2.0 (the License); you may
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| 17 | * not use this file except in compliance with the License.
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| 18 | * You may obtain a copy of the License at
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| 19 | *
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| 20 | * www.apache.org/licenses/LICENSE-2.0
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| 21 | *
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| 22 | * Unless required by applicable law or agreed to in writing, software
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| 23 | * distributed under the License is distributed on an AS IS BASIS, WITHOUT
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| 24 | * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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| 25 | * See the License for the specific language governing permissions and
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| 26 | * limitations under the License.
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| 27 | */
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| 28 |
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| 29 | #include "arm_math.h"
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| 30 | #include "arm_common_tables.h"
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| 31 |
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| 32 | /**
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| 33 | * @ingroup groupFastMath
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| 34 | */
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| 35 |
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| 36 | /**
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| 37 | * @addtogroup cos
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| 38 | * @{
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| 39 | */
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| 40 |
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| 41 | /**
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| 42 | * @brief Fast approximation to the trigonometric cosine function for Q15 data.
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| 43 | * @param[in] x Scaled input value in radians.
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| 44 | * @return cos(x).
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| 45 | *
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| 46 | * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
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| 47 | * value in the range [0 2*pi).
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| 48 | */
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| 49 |
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| 50 | q15_t arm_cos_q15(
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| 51 | q15_t x)
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| 52 | {
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| 53 | q15_t cosVal; /* Temporary variables for input, output */
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| 54 | int32_t index; /* Index variables */
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| 55 | q15_t a, b; /* Four nearest output values */
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| 56 | q15_t fract; /* Temporary values for fractional values */
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| 57 |
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| 58 | /* add 0.25 (pi/2) to read sine table */
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| 59 | x = (uint16_t)x + 0x2000;
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| 60 | if (x < 0)
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| 61 | { /* convert negative numbers to corresponding positive ones */
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| 62 | x = (uint16_t)x + 0x8000;
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| 63 | }
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| 64 |
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| 65 | /* Calculate the nearest index */
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| 66 | index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
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| 67 |
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| 68 | /* Calculation of fractional value */
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| 69 | fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
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| 70 |
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| 71 | /* Read two nearest values of input value from the sin table */
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| 72 | a = sinTable_q15[index];
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| 73 | b = sinTable_q15[index+1];
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| 74 |
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| 75 | /* Linear interpolation process */
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| 76 | cosVal = (q31_t)(0x8000-fract)*a >> 16;
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| 77 | cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16);
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| 78 |
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| 79 | return cosVal << 1;
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| 80 | }
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| 81 |
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| 82 | /**
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| 83 | * @} end of cos group
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| 84 | */
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