arm_cos_f32.c

00001 /* ----------------------------------------------------------------------
00002  * Project:      CMSIS DSP Library
00003  * Title:        arm_cos_f32.c
00004  * Description:  Fast cosine calculation for floating-point values
00005  *
00006  * $Date:        27. January 2017
00007  * $Revision:    V.1.5.1
00008  *
00009  * Target Processor: Cortex-M cores
00010  * -------------------------------------------------------------------- */
00011 /*
00012  * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
00013  *
00014  * SPDX-License-Identifier: Apache-2.0
00015  *
00016  * Licensed under the Apache License, Version 2.0 (the License); you may
00017  * not use this file except in compliance with the License.
00018  * You may obtain a copy of the License at
00019  *
00020  * www.apache.org/licenses/LICENSE-2.0
00021  *
00022  * Unless required by applicable law or agreed to in writing, software
00023  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
00024  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00025  * See the License for the specific language governing permissions and
00026  * limitations under the License.
00027  */
00028 
00029 #include "arm_math.h"
00030 #include "arm_common_tables.h"
00031 /**
00032  * @ingroup groupFastMath
00033  */
00034 
00035 /**
00036  * @defgroup cos Cosine
00037  *
00038  * Computes the trigonometric cosine function using a combination of table lookup
00039  * and linear interpolation.  There are separate functions for
00040  * Q15, Q31, and floating-point data types.
00041  * The input to the floating-point version is in radians and in the range [0 2*pi) while the
00042  * fixed-point Q15 and Q31 have a scaled input with the range
00043  * [0 +0.9999] mapping to [0 2*pi).  The fixed-point range is chosen so that a
00044  * value of 2*pi wraps around to 0.
00045  *
00046  * The implementation is based on table lookup using 256 values together with linear interpolation.
00047  * The steps used are:
00048  *  -# Calculation of the nearest integer table index
00049  *  -# Compute the fractional portion (fract) of the table index.
00050  *  -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
00051  *
00052  * where
00053  * <pre>
00054  *    b=Table[index+0];
00055  *    c=Table[index+1];
00056  * </pre>
00057  */
00058 
00059  /**
00060  * @addtogroup cos
00061  * @{
00062  */
00063 
00064 /**
00065  * @brief  Fast approximation to the trigonometric cosine function for floating-point data.
00066  * @param[in] x input value in radians.
00067  * @return cos(x).
00068  */
00069 
00070 float32_t arm_cos_f32(
00071   float32_t x)
00072 {
00073   float32_t cosVal, fract, in;                   /* Temporary variables for input, output */
00074   uint16_t index;                                /* Index variable */
00075   float32_t a, b;                                /* Two nearest output values */
00076   int32_t n;
00077   float32_t findex;
00078 
00079   /* input x is in radians */
00080   /* 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 */
00081   in = x * 0.159154943092f + 0.25f;
00082 
00083   /* Calculation of floor value of input */
00084   n = (int32_t) in;
00085 
00086   /* Make negative values towards -infinity */
00087   if (in < 0.0f)
00088   {
00089     n--;
00090   }
00091 
00092   /* Map input value to [0 1] */
00093   in = in - (float32_t) n;
00094 
00095   /* Calculation of index of the table */
00096   findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
00097   index = ((uint16_t)findex) & 0x1ff;
00098 
00099   /* fractional value calculation */
00100   fract = findex - (float32_t) index;
00101 
00102   /* Read two nearest values of input value from the cos table */
00103   a = sinTable_f32[index];
00104   b = sinTable_f32[index+1];
00105 
00106   /* Linear interpolation process */
00107   cosVal = (1.0f-fract)*a + fract*b;
00108 
00109   /* Return the output value */
00110   return (cosVal);
00111 }
00112 
00113 /**
00114  * @} end of cos group
00115  */
00116