Diff: FastMathFunctions/arm_sqrt_q15.c

Revision:

0:3d9c67d97d6f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FastMathFunctions/arm_sqrt_q15.c	Mon Jul 28 15:03:15 2014 +0000
@@ -0,0 +1,155 @@
+/* ----------------------------------------------------------------------     
+* Copyright (C) 2010-2014 ARM Limited. All rights reserved.  
+*     
+* $Date:        12. March 2014
+* $Revision: 	V1.4.3
+*     
+* Project:      CMSIS DSP Library  
+* Title:		arm_sqrt_q15.c     
+*     
+* Description:	Q15 square root function.    
+*     
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*  
+* Redistribution and use in source and binary forms, with or without 
+* modification, are permitted provided that the following conditions
+* are met:
+*   - Redistributions of source code must retain the above copyright
+*     notice, this list of conditions and the following disclaimer.
+*   - Redistributions in binary form must reproduce the above copyright
+*     notice, this list of conditions and the following disclaimer in
+*     the documentation and/or other materials provided with the 
+*     distribution.
+*   - Neither the name of ARM LIMITED nor the names of its contributors
+*     may be used to endorse or promote products derived from this
+*     software without specific prior written permission.
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
+* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+* POSSIBILITY OF SUCH DAMAGE. 
+* -------------------------------------------------------------------- */
+#include "arm_math.h"
+#include "arm_common_tables.h"
+
+
+/**     
+ * @ingroup groupFastMath     
+ */
+
+/**     
+ * @addtogroup SQRT     
+ * @{     
+ */
+
+  /**    
+   * @brief  Q15 square root function.    
+   * @param[in]   in     input value.  The range of the input value is [0 +1) or 0x0000 to 0x7FFF.    
+   * @param[out]  *pOut  square root of input value.    
+   * @return The function returns ARM_MATH_SUCCESS if the input value is positive
+   * and ARM_MATH_ARGUMENT_ERROR if the input is negative.  For
+   * negative inputs, the function returns *pOut = 0.
+   */
+
+arm_status arm_sqrt_q15(
+  q15_t in,
+  q15_t * pOut)
+{
+  q15_t number, temp1, var1, signBits1, half;
+  q31_t bits_val1;
+  float32_t temp_float1;
+  union
+  {
+    q31_t fracval;
+    float32_t floatval;
+  } tempconv;
+
+  number = in;
+
+  /* If the input is a positive number then compute the signBits. */
+  if(number > 0)
+  {
+    signBits1 = __CLZ(number) - 17;
+
+    /* Shift by the number of signBits1 */
+    if((signBits1 % 2) == 0)
+    {
+      number = number << signBits1;
+    }
+    else
+    {
+      number = number << (signBits1 - 1);
+    }
+
+    /* Calculate half value of the number */
+    half = number >> 1;
+    /* Store the number for later use */
+    temp1 = number;
+
+    /*Convert to float */
+    temp_float1 = number * 3.051757812500000e-005f;
+    /*Store as integer */
+    tempconv.floatval = temp_float1;
+    bits_val1 = tempconv.fracval;
+    /* Subtract the shifted value from the magic number to give intial guess */
+    bits_val1 = 0x5f3759df - (bits_val1 >> 1);  // gives initial guess  
+    /* Store as float */
+    tempconv.fracval = bits_val1;
+    temp_float1 = tempconv.floatval;
+    /* Convert to integer format */
+    var1 = (q31_t) (temp_float1 * 16384);
+
+    /* 1st iteration */
+    var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
+                                     ((q15_t)
+                                      ((((q15_t)
+                                         (((q31_t) var1 * var1) >> 15)) *
+                                        (q31_t) half) >> 15))) >> 15)) << 2;
+    /* 2nd iteration */
+    var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
+                                     ((q15_t)
+                                      ((((q15_t)
+                                         (((q31_t) var1 * var1) >> 15)) *
+                                        (q31_t) half) >> 15))) >> 15)) << 2;
+    /* 3rd iteration */
+    var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
+                                     ((q15_t)
+                                      ((((q15_t)
+                                         (((q31_t) var1 * var1) >> 15)) *
+                                        (q31_t) half) >> 15))) >> 15)) << 2;
+
+    /* Multiply the inverse square root with the original value */
+    var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
+
+    /* Shift the output down accordingly */
+    if((signBits1 % 2) == 0)
+    {
+      var1 = var1 >> (signBits1 / 2);
+    }
+    else
+    {
+      var1 = var1 >> ((signBits1 - 1) / 2);
+    }
+    *pOut = var1;
+
+    return (ARM_MATH_SUCCESS);
+  }
+  /* If the number is a negative number then store zero as its square root value */
+  else
+  {
+    *pOut = 0;
+    return (ARM_MATH_ARGUMENT_ERROR);
+  }
+}
+
+/**     
+ * @} end of SQRT group     
+ */