lib/main/CMSIS/DSP/Source/FastMathFunctions/arm_sqrt_q15.c

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