1 /* ----------------------------------------------------------------------
2 * Project: CMSIS DSP Library
3 * Title: arm_cos_f32.c
4 * Description: Fast cosine calculation for floating-point values
5 *
6 * $Date: 23 April 2021
7 * $Revision: V1.9.0
8 *
9 * Target Processor: Cortex-M and Cortex-A cores
10 * -------------------------------------------------------------------- */
11 /*
12 * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
13 *
14 * SPDX-License-Identifier: Apache-2.0
15 *
16 * Licensed under the Apache License, Version 2.0 (the License); you may
17 * not use this file except in compliance with the License.
18 * You may obtain a copy of the License at
19 *
20 * www.apache.org/licenses/LICENSE-2.0
21 *
22 * Unless required by applicable law or agreed to in writing, software
23 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
24 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
25 * See the License for the specific language governing permissions and
26 * limitations under the License.
27 */
28
29 #include "dsp/fast_math_functions.h"
30 #include "arm_common_tables.h"
31
32 /**
33 @ingroup groupFastMath
34 */
35
36 /**
37 @defgroup cos Cosine
38
39 Computes the trigonometric cosine function using a combination of table lookup
40 and linear interpolation. There are separate functions for
41 Q15, Q31, and floating-point data types.
42 The input to the floating-point version is in radians while the
43 fixed-point Q15 and Q31 have a scaled input with the range
44 [0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
45 value of 2*pi wraps around to 0.
46
47 The implementation is based on table lookup using 512 values together with linear interpolation.
48 The steps used are:
49 -# Calculation of the nearest integer table index
50 -# Compute the fractional portion (fract) of the table index.
51 -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
52
53 where
54 <pre>
55 a = Table[index];
56 b = Table[index+1];
57 </pre>
58 */
59
60 /**
61 @addtogroup cos
62 @{
63 */
64
65 /**
66 @brief Fast approximation to the trigonometric cosine function for floating-point data.
67 @param[in] x input value in radians
68 @return cos(x)
69 */
arm_cos_f32(float32_t x)70 float32_t arm_cos_f32(
71 float32_t x)
72 {
73 float32_t cosVal, fract, in; /* Temporary input, output variables */
74 uint16_t index; /* Index variable */
75 float32_t a, b; /* Two nearest output values */
76 int32_t n;
77 float32_t findex;
78
79 /* input x is in radians */
80 /* Scale input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
81 in = x * 0.159154943092f + 0.25f;
82
83 /* Calculation of floor value of input */
84 n = (int32_t) in;
85
86 /* Make negative values towards -infinity */
87 if (in < 0.0f)
88 {
89 n--;
90 }
91
92 /* Map input value to [0 1] */
93 in = in - (float32_t) n;
94
95 /* Calculation of index of the table */
96 findex = (float32_t)FAST_MATH_TABLE_SIZE * in;
97 index = (uint16_t)findex;
98
99 /* when "in" is exactly 1, we need to rotate the index down to 0 */
100 if (index >= FAST_MATH_TABLE_SIZE) {
101 index = 0;
102 findex -= (float32_t)FAST_MATH_TABLE_SIZE;
103 }
104
105 /* fractional value calculation */
106 fract = findex - (float32_t) index;
107
108 /* Read two nearest values of input value from the cos table */
109 a = sinTable_f32[index];
110 b = sinTable_f32[index+1];
111
112 /* Linear interpolation process */
113 cosVal = (1.0f - fract) * a + fract * b;
114
115 /* Return output value */
116 return (cosVal);
117 }
118
119 /**
120 @} end of cos group
121 */
122
