Subversion Repositories DashDisplay

Rev

Go to most recent revision | Blame | Compare with Previous | Last modification | View Log | Download | RSS feed

  1. /* ----------------------------------------------------------------------    
  2. * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
  3. *    
  4. * $Date:        19. March 2015
  5. * $Revision:    V.1.4.5
  6. *    
  7. * Project:          CMSIS DSP Library    
  8. * Title:                arm_cos_q31.c    
  9. *    
  10. * Description:  Fast cosine calculation for Q31 values.  
  11. *    
  12. * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13. *  
  14. * Redistribution and use in source and binary forms, with or without
  15. * modification, are permitted provided that the following conditions
  16. * are met:
  17. *   - Redistributions of source code must retain the above copyright
  18. *     notice, this list of conditions and the following disclaimer.
  19. *   - Redistributions in binary form must reproduce the above copyright
  20. *     notice, this list of conditions and the following disclaimer in
  21. *     the documentation and/or other materials provided with the
  22. *     distribution.
  23. *   - Neither the name of ARM LIMITED nor the names of its contributors
  24. *     may be used to endorse or promote products derived from this
  25. *     software without specific prior written permission.
  26. *
  27. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28. * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29. * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30. * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31. * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32. * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33. * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34. * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35. * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36. * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37. * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38. * POSSIBILITY OF SUCH DAMAGE.  
  39. * -------------------------------------------------------------------- */
  40.  
  41. #include "arm_math.h"
  42. #include "arm_common_tables.h"
  43.  
  44. /**    
  45.  * @ingroup groupFastMath    
  46.  */
  47.  
  48.  /**    
  49.  * @addtogroup cos    
  50.  * @{    
  51.  */
  52.  
  53. /**  
  54.  * @brief Fast approximation to the trigonometric cosine function for Q31 data.  
  55.  * @param[in] x Scaled input value in radians.  
  56.  * @return  cos(x).  
  57.  *  
  58.  * The Q31 input value is in the range [0 +0.9999] and is mapped to a radian
  59.  * value in the range [0 2*pi).
  60.  */
  61.  
  62. q31_t arm_cos_q31(
  63.   q31_t x)
  64. {
  65.   q31_t cosVal;                                  /* Temporary variables for input, output */
  66.   int32_t index;                                 /* Index variables */
  67.   q31_t a, b;                                    /* Four nearest output values */
  68.   q31_t fract;                                   /* Temporary values for fractional values */
  69.  
  70.   /* add 0.25 (pi/2) to read sine table */
  71.   x += 0x20000000;
  72.   if(x < 0)
  73.   {   /* convert negative numbers to corresponding positive ones */
  74.       x = x + 0x80000000;
  75.   }
  76.  
  77.   /* Calculate the nearest index */
  78.   index = (uint32_t)x >> FAST_MATH_Q31_SHIFT;
  79.  
  80.   /* Calculation of fractional value */
  81.   fract = (x - (index << FAST_MATH_Q31_SHIFT)) << 9;
  82.  
  83.   /* Read two nearest values of input value from the sin table */
  84.   a = sinTable_q31[index];
  85.   b = sinTable_q31[index+1];
  86.  
  87.   /* Linear interpolation process */
  88.   cosVal = (q63_t)(0x80000000-fract)*a >> 32;
  89.   cosVal = (q31_t)((((q63_t)cosVal << 32) + ((q63_t)fract*b)) >> 32);
  90.  
  91.   return cosVal << 1;
  92. }
  93.  
  94. /**    
  95.  * @} end of cos group    
  96.  */
  97.