arm_sin_q15.c

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/* ----------------------------------------------------------------------    
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
*    
* $Date:        19. March 2015
* $Revision:    V.1.4.5
*    
* Project:      CMSIS DSP Library    
* Title:        arm_sin_q15.c    
*    
* Description:  Fast sine 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
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*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
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* -------------------------------------------------------------------- */

#include "arm_math.h"
#include "arm_common_tables.h"

q15_t arm_sin_q15(
  q15_t x)
{
  q15_t sinVal;                                  /* 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 */

  /* 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 */
  sinVal = (q31_t)(0x8000-fract)*a >> 16;
  sinVal = (q15_t)((((q31_t)sinVal << 16) + ((q31_t)fract*b)) >> 16);

  return sinVal << 1;
}