Official ARM version: v5.6.0

DSP/Source/FastMathFunctions/arm_cos_f32.c

@@ -3,13 +3,13 @@
  * Title:        arm_cos_f32.c
  * Description:  Fast cosine calculation for floating-point values
  *
- * $Date:        27. January 2017
- * $Revision:    V.1.5.1
+ * $Date:        18. March 2019
+ * $Revision:    V1.6.0
  *
  * Target Processor: Cortex-M cores
  * -------------------------------------------------------------------- */
 /*
- * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
+ * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -28,56 +28,57 @@
 
 #include "arm_math.h"
 #include "arm_common_tables.h"
+
 /**
- * @ingroup groupFastMath
+  @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>
- */
+  @defgroup cos Cosine
 
- /**
- * @addtogroup cos
- * @{
+  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 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];
+     c = Table[index+1];
+  </pre>
  */
 
 /**
- * @brief  Fast approximation to the trigonometric cosine function for floating-point data.
- * @param[in] x input value in radians.
- * @return cos(x).
+  @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 */
+  float32_t cosVal, fract, in;                   /* Temporary input, output variables */
   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 */
+  /* Scale 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 */
@@ -93,8 +94,14 @@ float32_t arm_cos_f32(
   in = in - (float32_t) n;
 
   /* Calculation of index of the table */
-  findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
-  index = ((uint16_t)findex) & 0x1ff;
+  findex = (float32_t)FAST_MATH_TABLE_SIZE * in;
+  index = (uint16_t)findex;
+
+  /* when "in" is exactly 1, we need to rotate the index down to 0 */
+  if (index >= FAST_MATH_TABLE_SIZE) {
+    index = 0;
+    findex -= (float32_t)FAST_MATH_TABLE_SIZE;
+  }
 
   /* fractional value calculation */
   fract = findex - (float32_t) index;
@@ -104,12 +111,12 @@ float32_t arm_cos_f32(
   b = sinTable_f32[index+1];
 
   /* Linear interpolation process */
-  cosVal = (1.0f-fract)*a + fract*b;
+  cosVal = (1.0f - fract) * a + fract * b;
 
-  /* Return the output value */
+  /* Return output value */
   return (cosVal);
 }
 
 /**
- * @} end of cos group
+  @} end of cos group
  */