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1 /* ----------------------------------------------------------------------
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2 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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3 *
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4 * $Date: 19. October 2015
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5 * $Revision: V.1.4.5 a
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6 *
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7 * Project: CMSIS DSP Library
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8 * Title: arm_sqrt_q15.c
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9 *
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10 * Description: Q15 square root function.
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11 *
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12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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13 *
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14 * Redistribution and use in source and binary forms, with or without
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15 * modification, are permitted provided that the following conditions
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16 * are met:
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17 * - Redistributions of source code must retain the above copyright
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18 * notice, this list of conditions and the following disclaimer.
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19 * - Redistributions in binary form must reproduce the above copyright
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20 * notice, this list of conditions and the following disclaimer in
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21 * the documentation and/or other materials provided with the
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22 * distribution.
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23 * - Neither the name of ARM LIMITED nor the names of its contributors
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24 * may be used to endorse or promote products derived from this
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25 * software without specific prior written permission.
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26 *
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27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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38 * POSSIBILITY OF SUCH DAMAGE.
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39 * -------------------------------------------------------------------- */
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40 #include "arm_math.h"
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41 #include "arm_common_tables.h"
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42
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43
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44 /**
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45 * @ingroup groupFastMath
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46 */
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47
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48 /**
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49 * @addtogroup SQRT
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50 * @{
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51 */
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52
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53 /**
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54 * @brief Q15 square root function.
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55 * @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
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56 * @param[out] *pOut square root of input value.
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57 * @return The function returns ARM_MATH_SUCCESS if the input value is positive
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58 * and ARM_MATH_ARGUMENT_ERROR if the input is negative. For
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59 * negative inputs, the function returns *pOut = 0.
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60 */
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61
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62 arm_status arm_sqrt_q15(
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63 q15_t in,
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64 q15_t * pOut)
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65 {
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66 q15_t number, temp1, var1, signBits1, half;
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67 q31_t bits_val1;
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68 float32_t temp_float1;
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69 union
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70 {
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71 q31_t fracval;
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72 float32_t floatval;
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73 } tempconv;
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74
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75 number = in;
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76
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77 /* If the input is a positive number then compute the signBits. */
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78 if(number > 0)
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79 {
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80 signBits1 = __CLZ(number) - 17;
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81
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82 /* Shift by the number of signBits1 */
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83 if((signBits1 % 2) == 0)
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84 {
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85 number = number << signBits1;
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86 }
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87 else
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88 {
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89 number = number << (signBits1 - 1);
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90 }
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91
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92 /* Calculate half value of the number */
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93 half = number >> 1;
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94 /* Store the number for later use */
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95 temp1 = number;
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96
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97 /* Convert to float */
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98 temp_float1 = number * 3.051757812500000e-005f;
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99 /*Store as integer */
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100 tempconv.floatval = temp_float1;
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101 bits_val1 = tempconv.fracval;
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102 /* Subtract the shifted value from the magic number to give intial guess */
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103 bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */
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104 /* Store as float */
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105 tempconv.fracval = bits_val1;
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106 temp_float1 = tempconv.floatval;
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107 /* Convert to integer format */
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108 var1 = (q31_t) (temp_float1 * 16384);
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109
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110 /* 1st iteration */
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111 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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112 ((q15_t)
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113 ((((q15_t)
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114 (((q31_t) var1 * var1) >> 15)) *
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115 (q31_t) half) >> 15))) >> 15)) << 2;
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116 /* 2nd iteration */
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117 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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118 ((q15_t)
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119 ((((q15_t)
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120 (((q31_t) var1 * var1) >> 15)) *
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121 (q31_t) half) >> 15))) >> 15)) << 2;
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122 /* 3rd iteration */
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123 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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124 ((q15_t)
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125 ((((q15_t)
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126 (((q31_t) var1 * var1) >> 15)) *
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127 (q31_t) half) >> 15))) >> 15)) << 2;
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128
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129 /* Multiply the inverse square root with the original value */
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130 var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
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131
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132 /* Shift the output down accordingly */
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133 if((signBits1 % 2) == 0)
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134 {
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135 var1 = var1 >> (signBits1 / 2);
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136 }
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137 else
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138 {
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139 var1 = var1 >> ((signBits1 - 1) / 2);
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140 }
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141 *pOut = var1;
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142
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143 return (ARM_MATH_SUCCESS);
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144 }
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145 /* If the number is a negative number then store zero as its square root value */
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146 else
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147 {
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148 *pOut = 0;
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149 return (ARM_MATH_ARGUMENT_ERROR);
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150 }
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151 }
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152
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153 /**
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154 * @} end of SQRT group
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155 */
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