arm_cos_q15.c 3.4 KB

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  1. /* ----------------------------------------------------------------------
  2. * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
  3. *
  4. * $Date: 12. March 2014
  5. * $Revision: V1.4.4
  6. *
  7. * Project: CMSIS DSP Library
  8. * Title: arm_cos_q15.c
  9. *
  10. * Description: Fast cosine calculation for Q15 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. #include "arm_math.h"
  41. #include "arm_common_tables.h"
  42. /**
  43. * @ingroup groupFastMath
  44. */
  45. /**
  46. * @addtogroup cos
  47. * @{
  48. */
  49. /**
  50. * @brief Fast approximation to the trigonometric cosine function for Q15 data.
  51. * @param[in] x Scaled input value in radians.
  52. * @return cos(x).
  53. *
  54. * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
  55. * value in the range [0 2*pi).
  56. */
  57. q15_t arm_cos_q15(
  58. q15_t x)
  59. {
  60. q15_t sinVal; /* Temporary variables for input, output */
  61. int32_t index; /* Index variables */
  62. q15_t a, b; /* Four nearest output values */
  63. q15_t fract; /* Temporary values for fractional values */
  64. /* add 0.25 (pi/2) to read sine table */
  65. x += 0x2000;
  66. if(x < 0)
  67. { /* convert negative numbers to corresponding positive ones */
  68. x = x + 0x8000;
  69. }
  70. /* Calculate the nearest index */
  71. index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
  72. /* Calculation of fractional value */
  73. fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
  74. /* Read two nearest values of input value from the sin table */
  75. a = sinTable_q15[index];
  76. b = sinTable_q15[index+1];
  77. /* Linear interpolation process */
  78. sinVal = (q31_t)(0x8000-fract)*a >> 16;
  79. sinVal = (q15_t)((((q31_t)sinVal << 16) + ((q31_t)fract*b)) >> 16);
  80. return sinVal << 1;
  81. }
  82. /**
  83. * @} end of cos group
  84. */