1 /* ----------------------------------------------------------------------
2 * Project: CMSIS DSP Library
3 * Title: arm_sqrt_q15.c
4 * Description: Q15 square root function
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 SQRT
38 @{
39 */
40
41 /**
42 @brief Q15 square root function.
43 @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF
44 @param[out] pOut points to square root of input value
45 @return execution status
46 - \ref ARM_MATH_SUCCESS : input value is positive
47 - \ref ARM_MATH_ARGUMENT_ERROR : input value is negative; *pOut is set to 0
48 */
49
arm_sqrt_q15(q15_t in,q15_t * pOut)50 arm_status arm_sqrt_q15(
51 q15_t in,
52 q15_t * pOut)
53 {
54 q31_t bits_val1;
55 q15_t number, temp1, var1, signBits1, half;
56 float32_t temp_float1;
57 union
58 {
59 q31_t fracval;
60 float32_t floatval;
61 } tempconv;
62
63 number = in;
64
65 /* If the input is a positive number then compute the signBits. */
66 if (number > 0)
67 {
68 signBits1 = __CLZ(number) - 17;
69
70 /* Shift by the number of signBits1 */
71 if ((signBits1 % 2) == 0)
72 {
73 number = number << signBits1;
74 }
75 else
76 {
77 number = number << (signBits1 - 1);
78 }
79
80 /* Calculate half value of the number */
81 half = number >> 1;
82 /* Store the number for later use */
83 temp1 = number;
84
85 /* Convert to float */
86 temp_float1 = number * 3.051757812500000e-005f;
87 /* Store as integer */
88 tempconv.floatval = temp_float1;
89 bits_val1 = tempconv.fracval;
90 /* Subtract the shifted value from the magic number to give intial guess */
91 bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
92 /* Store as float */
93 tempconv.fracval = bits_val1;
94 temp_float1 = tempconv.floatval;
95 /* Convert to integer format */
96 var1 = (q31_t) (temp_float1 * 16384);
97
98 /* 1st iteration */
99 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
100 ((q15_t)
101 ((((q15_t)
102 (((q31_t) var1 * var1) >> 15)) *
103 (q31_t) half) >> 15))) >> 15)) << 2;
104 /* 2nd iteration */
105 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
106 ((q15_t)
107 ((((q15_t)
108 (((q31_t) var1 * var1) >> 15)) *
109 (q31_t) half) >> 15))) >> 15)) << 2;
110 /* 3rd iteration */
111 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
112 ((q15_t)
113 ((((q15_t)
114 (((q31_t) var1 * var1) >> 15)) *
115 (q31_t) half) >> 15))) >> 15)) << 2;
116
117 /* Multiply the inverse square root with the original value */
118 var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
119
120 /* Shift the output down accordingly */
121 if ((signBits1 % 2) == 0)
122 {
123 var1 = var1 >> (signBits1 / 2);
124 }
125 else
126 {
127 var1 = var1 >> ((signBits1 - 1) / 2);
128 }
129 *pOut = var1;
130
131 return (ARM_MATH_SUCCESS);
132 }
133 /* If the number is a negative number then store zero as its square root value */
134 else
135 {
136 *pOut = 0;
137
138 return (ARM_MATH_ARGUMENT_ERROR);
139 }
140 }
141
142 /**
143 @} end of SQRT group
144 */
145
