Eli Hughes / CMSIS_DSP_401

V4.0.1 of the ARM CMSIS DSP libraries. Note that arm_bitreversal2.s, arm_cfft_f32.c and arm_rfft_fast_f32.c had to be removed. arm_bitreversal2.s will not assemble with the online tools. So, the fast f32 FFT functions are not yet available. All the other FFT functions are available.

Dependents:   MPU9150_Example fir_f32 fir_f32 MPU9150_nucleo_noni2cdev ... more

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Variance
Functions

Variance
[Statistics Functions]

Calculates the variance of the elements in the input vector. More...

Functions

void arm_var_f32 (float32_t *pSrc, uint32_t blockSize, float32_t *pResult)
 Variance of the elements of a floating-point vector.
void arm_var_q15 (q15_t *pSrc, uint32_t blockSize, q15_t *pResult)
 Variance of the elements of a Q15 vector.
void arm_var_q31 (q31_t *pSrc, uint32_t blockSize, q31_t *pResult)
 Variance of the elements of a Q31 vector.

Detailed Description

Calculates the variance of the elements in the input vector.

The underlying algorithm is used:

    
 	Result = (sumOfSquares - sum2 / blockSize) / (blockSize - 1)
	   where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
	                   sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]

There are separate functions for floating point, Q31, and Q15 data types.

Function Documentation

void arm_var_f32 ( float32_t *  pSrc,
uint32_t  blockSize,
float32_t *  pResult 
)

Variance of the elements of a floating-point vector.

Parameters:
[in]*pSrcpoints to the input vector
[in]blockSizelength of the input vector
[out]*pResultvariance value returned here
Returns:
none.

Definition at line 80 of file arm_var_f32.c.

void arm_var_q15 ( q15_t *  pSrc,
uint32_t  blockSize,
q15_t *  pResult 
)

Variance of the elements of a Q15 vector.

Parameters:
[in]*pSrcpoints to the input vector
[in]blockSizelength of the input vector
[out]*pResultvariance value returned here
Returns:
none.

Scaling and Overflow Behavior:

The function is implemented using a 64-bit internal accumulator. The input is represented in 1.15 format. Intermediate multiplication yields a 2.30 format, and this result is added without saturation to a 64-bit accumulator in 34.30 format. With 33 guard bits in the accumulator, there is no risk of overflow, and the full precision of the intermediate multiplication is preserved. Finally, the 34.30 result is truncated to 34.15 format by discarding the lower 15 bits, and then saturated to yield a result in 1.15 format.

Definition at line 75 of file arm_var_q15.c.

void arm_var_q31 ( q31_t *  pSrc,
uint32_t  blockSize,
q31_t *  pResult 
)

Variance of the elements of a Q31 vector.

Parameters:
[in]*pSrcpoints to the input vector
[in]blockSizelength of the input vector
[out]*pResultvariance value returned here
Returns:
none.

Scaling and Overflow Behavior:

The function is implemented using an internal 64-bit accumulator. The input is represented in 1.31 format, which is then downshifted by 8 bits which yields 1.23, and intermediate multiplication yields a 2.46 format. The accumulator maintains full precision of the intermediate multiplication results, but provides only a 16 guard bits. There is no saturation on intermediate additions. If the accumulator overflows it wraps around and distorts the result. In order to avoid overflows completely the input signal must be scaled down by log2(blockSize)-8 bits, as a total of blockSize additions are performed internally. After division, internal variables should be Q18.46 Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value.

Definition at line 78 of file arm_var_q31.c.

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