| 1 | /* ----------------------------------------------------------------------
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| 2 | * Project: CMSIS DSP Library
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| 3 | * Title: arm_sqrt_q15.c
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| 4 | * Description: Q15 square root function
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| 5 | *
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| 6 | * $Date: 27. January 2017
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| 7 | * $Revision: V.1.5.1
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| 8 | *
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| 9 | * Target Processor: Cortex-M cores
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| 10 | * -------------------------------------------------------------------- */
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| 11 | /*
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| 12 | * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
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| 13 | *
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| 14 | * SPDX-License-Identifier: Apache-2.0
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| 15 | *
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| 16 | * Licensed under the Apache License, Version 2.0 (the License); you may
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| 17 | * not use this file except in compliance with the License.
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| 18 | * You may obtain a copy of the License at
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| 19 | *
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| 20 | * www.apache.org/licenses/LICENSE-2.0
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| 21 | *
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| 22 | * Unless required by applicable law or agreed to in writing, software
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| 23 | * distributed under the License is distributed on an AS IS BASIS, WITHOUT
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| 24 | * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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| 25 | * See the License for the specific language governing permissions and
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| 26 | * limitations under the License.
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| 27 | */
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| 28 |
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| 29 | #include "arm_math.h"
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| 30 | #include "arm_common_tables.h"
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| 31 |
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| 32 |
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| 33 | /**
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| 34 | * @ingroup groupFastMath
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| 35 | */
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| 36 |
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| 37 | /**
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| 38 | * @addtogroup SQRT
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| 39 | * @{
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| 40 | */
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| 41 |
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| 42 | /**
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| 43 | * @brief Q15 square root function.
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| 44 | * @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
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| 45 | * @param[out] *pOut square root of input value.
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| 46 | * @return The function returns ARM_MATH_SUCCESS if the input value is positive
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| 47 | * and ARM_MATH_ARGUMENT_ERROR if the input is negative. For
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| 48 | * negative inputs, the function returns *pOut = 0.
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| 49 | */
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| 50 |
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| 51 | arm_status arm_sqrt_q15(
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| 52 | q15_t in,
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| 53 | q15_t * pOut)
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| 54 | {
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| 55 | q15_t number, temp1, var1, signBits1, half;
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| 56 | q31_t bits_val1;
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| 57 | float32_t temp_float1;
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| 58 | union
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| 59 | {
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| 60 | q31_t fracval;
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| 61 | float32_t floatval;
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| 62 | } tempconv;
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| 63 |
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| 64 | number = in;
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| 65 |
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| 66 | /* If the input is a positive number then compute the signBits. */
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| 67 | if (number > 0)
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| 68 | {
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| 69 | signBits1 = __CLZ(number) - 17;
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| 70 |
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| 71 | /* Shift by the number of signBits1 */
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| 72 | if ((signBits1 % 2) == 0)
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| 73 | {
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| 74 | number = number << signBits1;
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| 75 | }
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| 76 | else
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| 77 | {
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| 78 | number = number << (signBits1 - 1);
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| 79 | }
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| 80 |
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| 81 | /* Calculate half value of the number */
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| 82 | half = number >> 1;
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| 83 | /* Store the number for later use */
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| 84 | temp1 = number;
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| 85 |
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| 86 | /* Convert to float */
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| 87 | temp_float1 = number * 3.051757812500000e-005f;
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| 88 | /*Store as integer */
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| 89 | tempconv.floatval = temp_float1;
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| 90 | bits_val1 = tempconv.fracval;
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| 91 | /* Subtract the shifted value from the magic number to give intial guess */
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| 92 | bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
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| 93 | /* Store as float */
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| 94 | tempconv.fracval = bits_val1;
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| 95 | temp_float1 = tempconv.floatval;
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| 96 | /* Convert to integer format */
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| 97 | var1 = (q31_t) (temp_float1 * 16384);
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| 98 |
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| 99 | /* 1st iteration */
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| 100 | var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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| 101 | ((q15_t)
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| 102 | ((((q15_t)
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| 103 | (((q31_t) var1 * var1) >> 15)) *
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| 104 | (q31_t) half) >> 15))) >> 15)) << 2;
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| 105 | /* 2nd iteration */
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| 106 | var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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| 107 | ((q15_t)
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| 108 | ((((q15_t)
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| 109 | (((q31_t) var1 * var1) >> 15)) *
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| 110 | (q31_t) half) >> 15))) >> 15)) << 2;
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| 111 | /* 3rd iteration */
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| 112 | var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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| 113 | ((q15_t)
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| 114 | ((((q15_t)
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| 115 | (((q31_t) var1 * var1) >> 15)) *
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| 116 | (q31_t) half) >> 15))) >> 15)) << 2;
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| 117 |
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| 118 | /* Multiply the inverse square root with the original value */
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| 119 | var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
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| 120 |
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| 121 | /* Shift the output down accordingly */
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| 122 | if ((signBits1 % 2) == 0)
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| 123 | {
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| 124 | var1 = var1 >> (signBits1 / 2);
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| 125 | }
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| 126 | else
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| 127 | {
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| 128 | var1 = var1 >> ((signBits1 - 1) / 2);
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| 129 | }
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| 130 | *pOut = var1;
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| 131 |
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| 132 | return (ARM_MATH_SUCCESS);
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| 133 | }
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| 134 | /* If the number is a negative number then store zero as its square root value */
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| 135 | else
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| 136 | {
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| 137 | *pOut = 0;
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| 138 | return (ARM_MATH_ARGUMENT_ERROR);
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| 139 | }
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| 140 | }
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| 141 |
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| 142 | /**
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| 143 | * @} end of SQRT group
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| 144 | */
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