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

Variance of the elements of a floating-point vector.

Parameters:

[in]	*pSrc	points to the input vector
[in]	blockSize	length of the input vector
[out]	*pResult	variance value returned here

Definition at line 80 of file arm_var_f32.c.

Variance of the elements of a Q15 vector.

Parameters:

[in]	*pSrc	points to the input vector
[in]	blockSize	length of the input vector
[out]	*pResult	variance value returned here

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.

Variance of the elements of a Q31 vector.

Parameters:

[in]	*pSrc	points to the input vector
[in]	blockSize	length of the input vector
[out]	*pResult	variance value returned here

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.