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| 56 | mjames | 1 | /* ---------------------------------------------------------------------- |
| 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 | |||
| 29 | #include "arm_math.h" |
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| 30 | #include "arm_common_tables.h" |
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| 31 | |||
| 32 | /** |
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| 33 | * @ingroup groupFastMath |
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| 34 | */ |
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| 35 | |||
| 36 | /** |
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| 37 | * @addtogroup cos |
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| 38 | * @{ |
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| 39 | */ |
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| 40 | |||
| 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 | |||
| 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 | |||
| 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 | |||
| 65 | /* Calculate the nearest index */ |
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| 66 | index = (uint32_t)x >> FAST_MATH_Q15_SHIFT; |
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| 67 | |||
| 68 | /* Calculation of fractional value */ |
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| 69 | fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9; |
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| 70 | |||
| 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 | |||
| 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 | |||
| 79 | return cosVal << 1; |
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| 80 | } |
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| 81 | |||
| 82 | /** |
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| 83 | * @} end of cos group |
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| 84 | */ |