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| bfc108 | 1 | /* ---------------------------------------------------------------------- |
| Q | 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 | ||
| 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 | */ | |
