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yaokon/Drivers/CMSIS/DSP/Source/FastMathFunctions/arm_cos_f32.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_cos_f32.c
+ * Description:  Fast cosine calculation for floating-point values
+ *
+ * $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
+ */
+
+/**
+ * @defgroup cos Cosine
+ *
+ * Computes the trigonometric cosine function using a combination of table lookup
+ * and linear interpolation.  There are separate functions for
+ * Q15, Q31, and floating-point data types.
+ * The input to the floating-point version is in radians and in the range [0 2*pi) while the
+ * fixed-point Q15 and Q31 have a scaled input with the range
+ * [0 +0.9999] mapping to [0 2*pi).  The fixed-point range is chosen so that a
+ * value of 2*pi wraps around to 0.
+ *
+ * The implementation is based on table lookup using 256 values together with linear interpolation.
+ * The steps used are:
+ *  -# Calculation of the nearest integer table index
+ *  -# Compute the fractional portion (fract) of the table index.
+ *  -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
+ *
+ * where
+ * <pre>
+ *    b=Table[index+0];
+ *    c=Table[index+1];
+ * </pre>
+ */
+
+ /**
+ * @addtogroup cos
+ * @{
+ */
+
+/**
+ * @brief  Fast approximation to the trigonometric cosine function for floating-point data.
+ * @param[in] x input value in radians.
+ * @return cos(x).
+ */
+
+float32_t arm_cos_f32(
+  float32_t x)
+{
+  float32_t cosVal, fract, in;                   /* Temporary variables for input, output */
+  uint16_t index;                                /* Index variable */
+  float32_t a, b;                                /* Two nearest output values */
+  int32_t n;
+  float32_t findex;
+
+  /* input x is in radians */
+  /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
+  in = x * 0.159154943092f + 0.25f;
+
+  /* Calculation of floor value of input */
+  n = (int32_t) in;
+
+  /* Make negative values towards -infinity */
+  if (in < 0.0f)
+  {
+    n--;
+  }
+
+  /* Map input value to [0 1] */
+  in = in - (float32_t) n;
+
+  /* Calculation of index of the table */
+  findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
+  index = ((uint16_t)findex) & 0x1ff;
+
+  /* fractional value calculation */
+  fract = findex - (float32_t) index;
+
+  /* Read two nearest values of input value from the cos table */
+  a = sinTable_f32[index];
+  b = sinTable_f32[index+1];
+
+  /* Linear interpolation process */
+  cosVal = (1.0f-fract)*a + fract*b;
+
+  /* Return the output value */
+  return (cosVal);
+}
+
+/**
+ * @} end of cos group
+ */