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| 2 | mjames | 1 | /* ---------------------------------------------------------------------- |
| 2 | * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
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| 3 | * |
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| 4 | * $Date: 19. March 2015 |
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| 5 | * $Revision: V.1.4.5 |
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| 6 | * |
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| 7 | * Project: CMSIS DSP Library |
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| 8 | * Title: arm_cos_q31.c |
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| 9 | * |
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| 10 | * Description: Fast cosine calculation for Q31 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 | |||
| 41 | #include "arm_math.h" |
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| 42 | #include "arm_common_tables.h" |
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| 43 | |||
| 44 | /** |
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| 45 | * @ingroup groupFastMath |
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| 46 | */ |
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| 47 | |||
| 48 | /** |
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| 49 | * @addtogroup cos |
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| 50 | * @{ |
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| 51 | */ |
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| 52 | |||
| 53 | /** |
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| 54 | * @brief Fast approximation to the trigonometric cosine function for Q31 data. |
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| 55 | * @param[in] x Scaled input value in radians. |
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| 56 | * @return cos(x). |
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| 57 | * |
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| 58 | * The Q31 input value is in the range [0 +0.9999] and is mapped to a radian |
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| 59 | * value in the range [0 2*pi). |
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| 60 | */ |
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| 61 | |||
| 62 | q31_t arm_cos_q31( |
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| 63 | q31_t x) |
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| 64 | { |
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| 65 | q31_t cosVal; /* Temporary variables for input, output */ |
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| 66 | int32_t index; /* Index variables */ |
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| 67 | q31_t a, b; /* Four nearest output values */ |
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| 68 | q31_t fract; /* Temporary values for fractional values */ |
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| 69 | |||
| 70 | /* add 0.25 (pi/2) to read sine table */ |
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| 71 | x += 0x20000000; |
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| 72 | if(x < 0) |
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| 73 | { /* convert negative numbers to corresponding positive ones */ |
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| 74 | x = x + 0x80000000; |
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| 75 | } |
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| 76 | |||
| 77 | /* Calculate the nearest index */ |
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| 78 | index = (uint32_t)x >> FAST_MATH_Q31_SHIFT; |
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| 79 | |||
| 80 | /* Calculation of fractional value */ |
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| 81 | fract = (x - (index << FAST_MATH_Q31_SHIFT)) << 9; |
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| 82 | |||
| 83 | /* Read two nearest values of input value from the sin table */ |
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| 84 | a = sinTable_q31[index]; |
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| 85 | b = sinTable_q31[index+1]; |
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| 86 | |||
| 87 | /* Linear interpolation process */ |
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| 88 | cosVal = (q63_t)(0x80000000-fract)*a >> 32; |
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| 89 | cosVal = (q31_t)((((q63_t)cosVal << 32) + ((q63_t)fract*b)) >> 32); |
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| 90 | |||
| 91 | return cosVal << 1; |
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| 92 | } |
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| 93 | |||
| 94 | /** |
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| 95 | * @} end of cos group |
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| 96 | */ |