tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/FastMathFunctions/arm_sqrt_q15.c

   1 /* ----------------------------------------------------------------------
   2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
   3 *
   4 * $Date:        17. January 2013
   5 * $Revision:    V1.4.1
   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  */