1 /* ----------------------------------------------------------------------
2 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
3 *
4 * $Date: 19. October 2015
5 * $Revision: V.1.4.5 a
6 *
7 * Project: CMSIS DSP Library
8 * Title: arm_sqrt_q15.c
9 *
10 * Description: Q15 square root function.
11 *
12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 * - Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 * - Redistributions in binary form must reproduce the above copyright
20 * notice, this list of conditions and the following disclaimer in
21 * the documentation and/or other materials provided with the
22 * distribution.
23 * - Neither the name of ARM LIMITED nor the names of its contributors
24 * may be used to endorse or promote products derived from this
25 * software without specific prior written permission.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
38 * POSSIBILITY OF SUCH DAMAGE.
39 * -------------------------------------------------------------------- */
40 #include "arm_math.h"
41 #include "arm_common_tables.h"
42
43
44 /**
45 * @ingroup groupFastMath
46 */
47
48 /**
49 * @addtogroup SQRT
50 * @{
51 */
52
53 /**
54 * @brief Q15 square root function.
55 * @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
56 * @param[out] *pOut square root of input value.
57 * @return The function returns ARM_MATH_SUCCESS if the input value is positive
58 * and ARM_MATH_ARGUMENT_ERROR if the input is negative. For
59 * negative inputs, the function returns *pOut = 0.
60 */
61
arm_sqrt_q15(q15_t in,q15_t * pOut)62 arm_status arm_sqrt_q15(
63 q15_t in,
64 q15_t * pOut)
65 {
66 q15_t number, temp1, var1, signBits1, half;
67 q31_t bits_val1;
68 float32_t temp_float1;
69 union
70 {
71 q31_t fracval;
72 float32_t floatval;
73 } tempconv;
74
75 number = in;
76
77 /* If the input is a positive number then compute the signBits. */
78 if(number > 0)
79 {
80 signBits1 = __CLZ(number) - 17;
81
82 /* Shift by the number of signBits1 */
83 if((signBits1 % 2) == 0)
84 {
85 number = number << signBits1;
86 }
87 else
88 {
89 number = number << (signBits1 - 1);
90 }
91
92 /* Calculate half value of the number */
93 half = number >> 1;
94 /* Store the number for later use */
95 temp1 = number;
96
97 /* Convert to float */
98 temp_float1 = number * 3.051757812500000e-005f;
99 /*Store as integer */
100 tempconv.floatval = temp_float1;
101 bits_val1 = tempconv.fracval;
102 /* Subtract the shifted value from the magic number to give intial guess */
103 bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
104 /* Store as float */
105 tempconv.fracval = bits_val1;
106 temp_float1 = tempconv.floatval;
107 /* Convert to integer format */
108 var1 = (q31_t) (temp_float1 * 16384);
109
110 /* 1st 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 /* 2nd iteration */
117 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
118 ((q15_t)
119 ((((q15_t)
120 (((q31_t) var1 * var1) >> 15)) *
121 (q31_t) half) >> 15))) >> 15)) << 2;
122 /* 3rd iteration */
123 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
124 ((q15_t)
125 ((((q15_t)
126 (((q31_t) var1 * var1) >> 15)) *
127 (q31_t) half) >> 15))) >> 15)) << 2;
128
129 /* Multiply the inverse square root with the original value */
130 var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
131
132 /* Shift the output down accordingly */
133 if((signBits1 % 2) == 0)
134 {
135 var1 = var1 >> (signBits1 / 2);
136 }
137 else
138 {
139 var1 = var1 >> ((signBits1 - 1) / 2);
140 }
141 *pOut = var1;
142
143 return (ARM_MATH_SUCCESS);
144 }
145 /* If the number is a negative number then store zero as its square root value */
146 else
147 {
148 *pOut = 0;
149 return (ARM_MATH_ARGUMENT_ERROR);
150 }
151 }
152
153 /**
154 * @} end of SQRT group
155 */
156