Subversion Repositories DashDisplay

Rev

Rev 5 | 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_f32.c    
  9. *    
  10. * Description:  Fast cosine calculation for floating-point 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.  * @ingroup groupFastMath    
  45.  */
  46.  
  47. /**    
  48.  * @defgroup cos Cosine    
  49.  *    
  50.  * Computes the trigonometric cosine function using a combination of table lookup  
  51.  * and cubic interpolation.  There are separate functions for  
  52.  * Q15, Q31, and floating-point data types.  
  53.  * The input to the floating-point version is in radians while the  
  54.  * fixed-point Q15 and Q31 have a scaled input with the range  
  55.  * [0 +0.9999] mapping to [0 2*pi).  The fixed-point range is chosen so that a
  56.  * value of 2*pi wraps around to 0.
  57.  *  
  58.  * The implementation is based on table lookup using 256 values together with cubic interpolation.  
  59.  * The steps used are:  
  60.  *  -# Calculation of the nearest integer table index  
  61.  *  -# Fetch the four table values a, b, c, and d    
  62.  *  -# Compute the fractional portion (fract) of the table index.  
  63.  *  -# Calculation of wa, wb, wc, wd    
  64.  *  -# The final result equals <code>a*wa + b*wb + c*wc + d*wd</code>  
  65.  *  
  66.  * where  
  67.  * <pre>    
  68.  *    a=Table[index-1];    
  69.  *    b=Table[index+0];    
  70.  *    c=Table[index+1];    
  71.  *    d=Table[index+2];    
  72.  * </pre>  
  73.  * and  
  74.  * <pre>    
  75.  *    wa=-(1/6)*fract.^3 + (1/2)*fract.^2 - (1/3)*fract;    
  76.  *    wb=(1/2)*fract.^3 - fract.^2 - (1/2)*fract + 1;    
  77.  *    wc=-(1/2)*fract.^3+(1/2)*fract.^2+fract;    
  78.  *    wd=(1/6)*fract.^3 - (1/6)*fract;    
  79.  * </pre>    
  80.  */
  81.  
  82.  /**    
  83.  * @addtogroup cos    
  84.  * @{    
  85.  */
  86.  
  87. /**  
  88.  * @brief  Fast approximation to the trigonometric cosine function for floating-point data.  
  89.  * @param[in] x input value in radians.  
  90.  * @return cos(x).  
  91.  */
  92.  
  93. float32_t arm_cos_f32(
  94.   float32_t x)
  95. {
  96.   float32_t cosVal, fract, in;                   /* Temporary variables for input, output */
  97.   uint16_t index;                                /* Index variable */
  98.   float32_t a, b;                                /* Two nearest output values */
  99.   int32_t n;
  100.   float32_t findex;
  101.  
  102.   /* input x is in radians */
  103.   /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
  104.   in = x * 0.159154943092f + 0.25f;
  105.  
  106.   /* Calculation of floor value of input */
  107.   n = (int32_t) in;
  108.  
  109.   /* Make negative values towards -infinity */
  110.   if(in < 0.0f)
  111.   {
  112.     n--;
  113.   }
  114.  
  115.   /* Map input value to [0 1] */
  116.   in = in - (float32_t) n;
  117.  
  118.   /* Calculation of index of the table */
  119.   findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
  120.   index = ((uint16_t)findex) & 0x1ff;
  121.  
  122.   /* fractional value calculation */
  123.   fract = findex - (float32_t) index;
  124.  
  125.   /* Read two nearest values of input value from the cos table */
  126.   a = sinTable_f32[index];
  127.   b = sinTable_f32[index+1];
  128.  
  129.   /* Linear interpolation process */
  130.   cosVal = (1.0f-fract)*a + fract*b;
  131.  
  132.   /* Return the output value */
  133.   return (cosVal);
  134. }
  135.  
  136. /**    
  137.  * @} end of cos group    
  138.  */
  139.