Diff: DSP/source/FastMathFunctions/arm_sqrt_q31.c

Revision:

0:eedb7d567a5d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DSP/source/FastMathFunctions/arm_sqrt_q31.c	Thu Apr 12 01:31:58 2018 +0000
@@ -0,0 +1,143 @@
+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_sqrt_q31.c
+ * Description:  Q31 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 Q31 square root function.
+ * @param[in]   in    input value.  The range of the input value is [0 +1) or 0x00000000 to 0x7FFFFFFF.
+ * @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_q31(
+  q31_t in,
+  q31_t * pOut)
+{
+  q31_t number, temp1, bits_val1, var1, signBits1, half;
+  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) - 1;
+
+    /* 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 * 4.6566128731e-010f;
+    /*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 * 1073741824);
+
+    /* 1st iteration */
+    var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
+                                     ((q31_t)
+                                      ((((q31_t)
+                                         (((q63_t) var1 * var1) >> 31)) *
+                                        (q63_t) half) >> 31))) >> 31)) << 2;
+    /* 2nd iteration */
+    var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
+                                     ((q31_t)
+                                      ((((q31_t)
+                                         (((q63_t) var1 * var1) >> 31)) *
+                                        (q63_t) half) >> 31))) >> 31)) << 2;
+    /* 3rd iteration */
+    var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
+                                     ((q31_t)
+                                      ((((q31_t)
+                                         (((q63_t) var1 * var1) >> 31)) *
+                                        (q63_t) half) >> 31))) >> 31)) << 2;
+
+    /* Multiply the inverse square root with the original value */
+    var1 = ((q31_t) (((q63_t) temp1 * var1) >> 31)) << 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
+ */
+