这个函数就几个参数，看看说明就好了吧
void arm_biquad_cascade_df1_q15 ( const arm_biquad_casd_df1_inst_q15 * S,
q15_t * pSrc,
q15_t * pDst,
uint32_t blockSize
)
Parameters
[in] *S points to an instance of the Q15 Biquad cascade structure.
[in] *pSrc points to the block of input data.
[out] *pDst points to the location where the output result is written.
[in] blockSize number of samples to process per call.
Returns
none.
Scaling and Overflow Behavior:
The function is implemented using a 64-bit internal accumulator. Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result. The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format. There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved. The accumulator is then shifted by postShift bits to truncate the result to 1.15 format by discarding the low 16 bits. Finally, the result is saturated to 1.15 format.
Refer to the function arm_biquad_cascade_df1_fast_q15() for a faster but less precise implementation of this filter for Cortex-M3 and Cortex-M4.
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