DSP library for MSP430 and MSP432 version 1_10_00_10搞不懂，请教问题？

Real forward FFT function with fixed scaling by two at each stage.

Details

Computes the forward discreet Fourier transform (DFT) of 16-bit real inputs. If the inputs are not already in bit reversed order the bit reversal parameter must be set. The output is scaled by a factor of two for each stage of the DFT.

This functions requires half the data storage and consumes roughly half the cycles and energy as running a complex FFT of the same length. When transforming purely real inputs, such as samples from an ADC or analog sensor, it is recommended to use the real FFT functions.

When using LEASC the twiddle table pointer can be set to NULL (zero) and the source data must be aligned to LENGTH*2 bytes. For example, a 256 point real FFT must be aligned to a 512 byte address in shared LEA memory.

Pseudo code

y = fft(real(x)) ./ (N/2)

Scaling

Each stage of the real FFT, with the exception of the final split stage, scales the result by a factor of 0.5. The output format can either be interpreted as the same type with (N/2) scaling or a different fixed point data type. This can be helpful when using the IQmathLib to process the results of the FFT, such as computing the magnitude or phase angle of the complex result.

Length	Input Type	Result Type
16	_q15	_q12
32	_q15	_q11
64	_q15	_q10
128	_q15	_q9
256	_q15	_q8
512	_q15	_q7
1024	_q15	_q6
2048	_q15	_q5
4096	_q15	_q4

The following table lists the applied scaling factor and resulting data type when the input is a 16-bit integer.

Length	Input Type	Result Type
16	int16_t	(int16_t)(result / 8)
32	int16_t	(int16_t)(result / 16)
64	int16_t	(int16_t)(result / 32)
128	int16_t	(int16_t)(result / 64)
256	int16_t	(int16_t)(result / 128)
512	int16_t	(int16_t)(result / 256)
1024	int16_t	(int16_t)(result / 512)
2048	int16_t	(int16_t)(result / 1024)
4096	int16_t	(int16_t)(result / 2048)

Parameters

params	Pointer to the real FFT parameter structure.
src	Pointer to the real data array to perform the FFT on.

Returns

Status of the operation.

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