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# vDSP_fftm_zropt

Computes a forward or inverse out-of-place, single-precision real FFT on multiple signals using a temporary buffer.

```
extern void vDSP_fftm_zropt(FFTSetup __Setup, const DSPSplitComplex *__A, vDSP_Stride __IA, vDSP_Stride __IMA, const DSPSplitComplex *__C, vDSP_Stride __IC, vDSP_Stride __IMC, const DSPSplitComplex *__Buffer, vDSP_Length __Log2N, vDSP_Length __M, FFTDirection __Direction);
```

## Parameters

`__Setup`

The FFT setup structure for this transform. The setup’s structure `Log2N` must be greater than or equal to this function’s `Log2N`.

`__A`

A pointer to the input data.

`__IA`

The stride between the elements in `A`, set to 1 for best performance.

`__IMA`

The increment, in complex elements, between input signals. This parameter also specifies the length of each input signal in split-complex format.

`__C`

A pointer to the output data.

`__IC`

The stride between the elements in `C`, set to 1 for best performance.

`__IMC`

The increment, in elements, between output signals. This parameter also specifies the length of each output signal.

`__Buffer`

A temporary vector that the operation uses for storing interim results. The real and imaginary parts of the buffer must both contain `2`Log2N`/2` elements. For best performance, the buffer addresses must be 16-byte aligned or better.

`__Log2N`

The base 2 exponent of the number of elements to process. For example, to process 1024 elements, specify 10 for parameter `Log2N`.

`__M`

The number of input signals.

`__Direction`

A flag that specifies the transform direction. Pass <doc://com.apple.documentation/documentation/kernel/1645049-anonymous/kfftdirection_forward> to transform from the time domain to the frequency domain. Pass <doc://com.apple.documentation/documentation/kernel/1645049-anonymous/kfftdirection_inverse> to transform from the frequency domain to the time domain.

## Discussion

> Tip:
> To learn how the vDSP library scales and arranges the FFT output, see <doc://com.apple.documentation/documentation/Accelerate/understanding-data-packing-for-fourier-transforms>.

---

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