| 1 | /* ----------------------------------------------------------------------
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| 2 | * Project: CMSIS DSP Library
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| 3 | * Title: arm_cos_f32.c
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| 4 | * Description: Fast cosine calculation for floating-point 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 | * @ingroup groupFastMath
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| 33 | */
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| 34 |
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| 35 | /**
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| 36 | * @defgroup cos Cosine
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| 37 | *
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| 38 | * Computes the trigonometric cosine function using a combination of table lookup
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| 39 | * and linear interpolation. There are separate functions for
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| 40 | * Q15, Q31, and floating-point data types.
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| 41 | * The input to the floating-point version is in radians and in the range [0 2*pi) while the
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| 42 | * fixed-point Q15 and Q31 have a scaled input with the range
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| 43 | * [0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
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| 44 | * value of 2*pi wraps around to 0.
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| 45 | *
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| 46 | * The implementation is based on table lookup using 256 values together with linear interpolation.
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| 47 | * The steps used are:
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| 48 | * -# Calculation of the nearest integer table index
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| 49 | * -# Compute the fractional portion (fract) of the table index.
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| 50 | * -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
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| 51 | *
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| 52 | * where
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| 53 | * <pre>
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| 54 | * b=Table[index+0];
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| 55 | * c=Table[index+1];
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| 56 | * </pre>
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| 57 | */
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| 58 |
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| 59 | /**
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| 60 | * @addtogroup cos
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| 61 | * @{
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| 62 | */
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| 63 |
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| 64 | /**
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| 65 | * @brief Fast approximation to the trigonometric cosine function for floating-point data.
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| 66 | * @param[in] x input value in radians.
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| 67 | * @return cos(x).
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| 68 | */
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| 69 |
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| 70 | float32_t arm_cos_f32(
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| 71 | float32_t x)
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| 72 | {
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| 73 | float32_t cosVal, fract, in; /* Temporary variables for input, output */
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| 74 | uint16_t index; /* Index variable */
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| 75 | float32_t a, b; /* Two nearest output values */
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| 76 | int32_t n;
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| 77 | float32_t findex;
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| 78 |
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| 79 | /* input x is in radians */
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| 80 | /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
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| 81 | in = x * 0.159154943092f + 0.25f;
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| 82 |
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| 83 | /* Calculation of floor value of input */
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| 84 | n = (int32_t) in;
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| 85 |
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| 86 | /* Make negative values towards -infinity */
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| 87 | if (in < 0.0f)
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| 88 | {
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| 89 | n--;
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| 90 | }
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| 91 |
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| 92 | /* Map input value to [0 1] */
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| 93 | in = in - (float32_t) n;
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| 94 |
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| 95 | /* Calculation of index of the table */
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| 96 | findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
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| 97 | index = ((uint16_t)findex) & 0x1ff;
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| 98 |
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| 99 | /* fractional value calculation */
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| 100 | fract = findex - (float32_t) index;
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| 101 |
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| 102 | /* Read two nearest values of input value from the cos table */
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| 103 | a = sinTable_f32[index];
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| 104 | b = sinTable_f32[index+1];
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| 105 |
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| 106 | /* Linear interpolation process */
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| 107 | cosVal = (1.0f-fract)*a + fract*b;
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| 108 |
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| 109 | /* Return the output value */
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| 110 | return (cosVal);
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| 111 | }
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| 112 |
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| 113 | /**
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| 114 | * @} end of cos group
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| 115 | */
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