1 /* ----------------------------------------------------------------------
2 * Project: CMSIS DSP Library
3 * Title: arm_cos_q15.c
4 * Description: Fast cosine calculation for Q15 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 @addtogroup cos
38 @{
39 */
40
41 /**
42 @brief Fast approximation to the trigonometric cosine function for Q15 data.
43 @param[in] x Scaled input value in radians
44 @return cos(x)
45
46 The Q15 input value is in the range [0 +0.9999] and is mapped to a radian value in the range [0 2*PI).
47 */
48
arm_cos_q15(q15_t x)49 q15_t arm_cos_q15(
50 q15_t x)
51 {
52 q15_t cosVal; /* Temporary input, output variables */
53 int32_t index; /* Index variable */
54 q15_t a, b; /* Two nearest output values */
55 q15_t fract; /* Temporary values for fractional values */
56
57 /* add 0.25 (pi/2) to read sine table */
58 x = (uint16_t)x + 0x2000;
59 if (x < 0)
60 { /* convert negative numbers to corresponding positive ones */
61 x = (uint16_t)x + 0x8000;
62 }
63
64 /* Calculate the nearest index */
65 index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
66
67 /* Calculation of fractional value */
68 fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
69
70 /* Read two nearest values of input value from the sin table */
71 a = sinTable_q15[index];
72 b = sinTable_q15[index+1];
73
74 /* Linear interpolation process */
75 cosVal = (q31_t) (0x8000 - fract) * a >> 16;
76 cosVal = (q15_t) ((((q31_t) cosVal << 16) + ((q31_t) fract * b)) >> 16);
77
78 /* Return output value */
79 return (cosVal << 1);
80 }
81
82 /**
83 @} end of cos group
84 */
85
