新版DSP库的三角函数sin和cos求解过程是通过查表再做简单的线性插值实现

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楼主 | 2018-8-4 16:04 | 只看该作者回帖奖励

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函数, DSP库, os, 线性, index

先做归一化，然查表代入公式(1.0f-fract)*a + fract*b获得结果。

float32_t arm_sin_f32(
  float32_t x)
{
  float32_t sinVal, 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 */
  in = x * 0.159154943092f;

  /* 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 &quot;in&quot; 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 sin table */
  a = sinTable_f32[index];
  b = sinTable_f32[index+1];

  /* Linear interpolation process */
  sinVal = (1.0f - fract) * a + fract * b;

  /* Return output value */
  return (sinVal);
}

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