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  1. /* ----------------------------------------------------------------------    
  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.  */
  156.