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yaokon/Drivers/CMSIS/DSP/Source/FastMathFunctions/arm_sqrt_q15.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_sqrt_q15.c
+ * Description:  Q15 square root function
+ *
+ * $Date:        27. January 2017
+ * $Revision:    V.1.5.1
+ *
+ * Target Processor: Cortex-M cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#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
+ */