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 /* ---------------------------------------------------------------------- * Project: CMSIS DSP Library * Title: arm_cos_f32.c * Description: Fast cosine calculation for floating-point values * * \$Date: 18. March 2019 * \$Revision: V1.6.0 * * Target Processor: Cortex-M cores * -------------------------------------------------------------------- */ /* * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved. * * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the License); you may * not use this file except in compliance with the License. * You may obtain a copy of the License at * * www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an AS IS BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "arm_math.h" #include "arm_common_tables.h" /** @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 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 (1.0f-fract)*a + fract*b; where
b = Table[index];
c = Table[index+1];
*/ /** @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 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 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 */ n = (int32_t) in; /* Make negative values towards -infinity */ if (in < 0.0f) { n--; } /* Map input value to [0 1] */ in = in - (float32_t) n; /* Calculation of index of the table */ 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; /* Read two nearest values of input value from the cos table */ a = sinTable_f32[index]; b = sinTable_f32[index+1]; /* Linear interpolation process */ cosVal = (1.0f - fract) * a + fract * b; /* Return output value */ return (cosVal); } /** @} end of cos group */