1 /* ----------------------------------------------------------------------
2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
4 * $Date: 17. January 2013
7 * Project: CMSIS DSP Library
8 * Title: arm_sqrt_q15.c
10 * Description: Q15 square root function.
12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
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
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.
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
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38 * POSSIBILITY OF SUCH DAMAGE.
39 * -------------------------------------------------------------------- */
41 #include "arm_common_tables.h"
45 * @ingroup groupFastMath
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.
62 arm_status arm_sqrt_q15(
66 q15_t number, temp1, var1, signBits1, half;
68 float32_t temp_float1;
77 /* If the input is a positive number then compute the signBits. */
80 signBits1 = __CLZ(number) - 17;
82 /* Shift by the number of signBits1 */
83 if((signBits1 % 2) == 0)
85 number = number << signBits1;
89 number = number << (signBits1 - 1);
92 /* Calculate half value of the number */
94 /* Store the number for later use */
98 temp_float1 = number * 3.051757812500000e-005f;
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
105 tempconv.fracval = bits_val1;
106 temp_float1 = tempconv.floatval;
107 /* Convert to integer format */
108 var1 = (q31_t) (temp_float1 * 16384);
111 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
114 (((q31_t) var1 * var1) >> 15)) *
115 (q31_t) half) >> 15))) >> 15)) << 2;
117 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
120 (((q31_t) var1 * var1) >> 15)) *
121 (q31_t) half) >> 15))) >> 15)) << 2;
123 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
126 (((q31_t) var1 * var1) >> 15)) *
127 (q31_t) half) >> 15))) >> 15)) << 2;
129 /* Multiply the inverse square root with the original value */
130 var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
132 /* Shift the output down accordingly */
133 if((signBits1 % 2) == 0)
135 var1 = var1 >> (signBits1 / 2);
139 var1 = var1 >> ((signBits1 - 1) / 2);
143 return (ARM_MATH_SUCCESS);
145 /* If the number is a negative number then store zero as its square root value */
149 return (ARM_MATH_ARGUMENT_ERROR);
154 * @} end of SQRT group