arm_cos_q15.c

00001 /* ----------------------------------------------------------------------
00002 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
00003 *
00004 * $Date:        07. September 2015
00005 * $Revision:    V.1.4.5 a
00006 *
00007 * Project:      CMSIS DSP Library
00008 * Title:        arm_cos_q15.c
00009 *
00010 * Description:  Fast cosine calculation for Q15 values.
00011 *
00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
00013 *
00014 * Redistribution and use in source and binary forms, with or without
00015 * modification, are permitted provided that the following conditions
00016 * are met:
00017 *   - Redistributions of source code must retain the above copyright
00018 *     notice, this list of conditions and the following disclaimer.
00019 *   - Redistributions in binary form must reproduce the above copyright
00020 *     notice, this list of conditions and the following disclaimer in
00021 *     the documentation and/or other materials provided with the
00022 *     distribution.
00023 *   - Neither the name of ARM LIMITED nor the names of its contributors
00024 *     may be used to endorse or promote products derived from this
00025 *     software without specific prior written permission.
00026 *
00027 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
00028 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
00029 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
00030 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
00031 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
00032 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
00033 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
00034 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
00035 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00036 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
00037 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
00038 * POSSIBILITY OF SUCH DAMAGE.
00039 * -------------------------------------------------------------------- */
00040 
00041 #include "arm_math.h"
00042 #include "arm_common_tables.h"
00043 
00044 /**
00045  * @ingroup groupFastMath
00046  */
00047 
00048  /**
00049  * @addtogroup cos
00050  * @{
00051  */
00052 
00053 /**
00054  * @brief Fast approximation to the trigonometric cosine function for Q15 data.
00055  * @param[in] x Scaled input value in radians.
00056  * @return  cos(x).
00057  *
00058  * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
00059  * value in the range [0 2*pi).
00060  */
00061 
00062 q15_t arm_cos_q15(
00063   q15_t x)
00064 {
00065   q15_t cosVal;                                  /* Temporary variables for input, output */
00066   int32_t index;                                 /* Index variables */
00067   q15_t a, b;                                    /* Four nearest output values */
00068   q15_t fract;                                   /* Temporary values for fractional values */
00069 
00070   /* add 0.25 (pi/2) to read sine table */
00071   x = (uint16_t)x + 0x2000;
00072   if(x < 0)
00073   {   /* convert negative numbers to corresponding positive ones */
00074       x = (uint16_t)x + 0x8000;
00075   }
00076 
00077   /* Calculate the nearest index */
00078   index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
00079 
00080   /* Calculation of fractional value */
00081   fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
00082 
00083   /* Read two nearest values of input value from the sin table */
00084   a = sinTable_q15[index];
00085   b = sinTable_q15[index+1];
00086 
00087   /* Linear interpolation process */
00088   cosVal = (q31_t)(0x8000-fract)*a >> 16;
00089   cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16);
00090 
00091   return cosVal << 1;
00092 }
00093 
00094 /**
00095  * @} end of cos group
00096  */