|
|
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 "in" 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);
}
|
|
发表于 2019-10-19 13:21:04
发表于 2019-10-19 15:08:33
楼主
