arm_cos_q15.c

00001 /* ----------------------------------------------------------------------
00002  * Project:      CMSIS DSP Library
00003  * Title:        arm_cos_q15.c
00004  * Description:  Fast cosine calculation for Q15 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 /**
00033  * @ingroup groupFastMath
00034  */
00035 
00036  /**
00037  * @addtogroup cos
00038  * @{
00039  */
00040 
00041 /**
00042  * @brief Fast approximation to the trigonometric cosine function for Q15 data.
00043  * @param[in] x Scaled input value in radians.
00044  * @return  cos(x).
00045  *
00046  * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
00047  * value in the range [0 2*pi).
00048  */
00049 
00050 q15_t arm_cos_q15(
00051   q15_t x)
00052 {
00053   q15_t cosVal;                                  /* Temporary variables for input, output */
00054   int32_t index;                                 /* Index variables */
00055   q15_t a, b;                                    /* Four nearest output values */
00056   q15_t fract;                                   /* Temporary values for fractional values */
00057 
00058   /* add 0.25 (pi/2) to read sine table */
00059   x = (uint16_t)x + 0x2000;
00060   if (x < 0)
00061   {   /* convert negative numbers to corresponding positive ones */
00062       x = (uint16_t)x + 0x8000;
00063   }
00064 
00065   /* Calculate the nearest index */
00066   index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
00067 
00068   /* Calculation of fractional value */
00069   fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
00070 
00071   /* Read two nearest values of input value from the sin table */
00072   a = sinTable_q15[index];
00073   b = sinTable_q15[index+1];
00074 
00075   /* Linear interpolation process */
00076   cosVal = (q31_t)(0x8000-fract)*a >> 16;
00077   cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16);
00078 
00079   return cosVal << 1;
00080 }
00081 
00082 /**
00083  * @} end of cos group
00084  */
00085