| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| * |
| * $Date: 07. September 2015 |
| * $Revision: V.1.4.5 a |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_cos_q15.c |
| * |
| * Description: Fast cosine calculation for Q15 values. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * - Neither the name of ARM LIMITED nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| * -------------------------------------------------------------------- */ |
| |
| #include "arm_math.h" |
| #include "arm_common_tables.h" |
| |
| /** |
| * @ingroup groupFastMath |
| */ |
| |
| /** |
| * @addtogroup cos |
| * @{ |
| */ |
| |
| /** |
| * @brief Fast approximation to the trigonometric cosine function for Q15 data. |
| * @param[in] x Scaled input value in radians. |
| * @return cos(x). |
| * |
| * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian |
| * value in the range [0 2*pi). |
| */ |
| |
| q15_t arm_cos_q15( |
| q15_t x) |
| { |
| q15_t cosVal; /* Temporary variables for input, output */ |
| int32_t index; /* Index variables */ |
| q15_t a, b; /* Four nearest output values */ |
| q15_t fract; /* Temporary values for fractional values */ |
| |
| /* add 0.25 (pi/2) to read sine table */ |
| x = (uint16_t)x + 0x2000; |
| if(x < 0) |
| { /* convert negative numbers to corresponding positive ones */ |
| x = (uint16_t)x + 0x8000; |
| } |
| |
| /* Calculate the nearest index */ |
| index = (uint32_t)x >> FAST_MATH_Q15_SHIFT; |
| |
| /* Calculation of fractional value */ |
| fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9; |
| |
| /* Read two nearest values of input value from the sin table */ |
| a = sinTable_q15[index]; |
| b = sinTable_q15[index+1]; |
| |
| /* Linear interpolation process */ |
| cosVal = (q31_t)(0x8000-fract)*a >> 16; |
| cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16); |
| |
| return cosVal << 1; |
| } |
| |
| /** |
| * @} end of cos group |
| */ |