# vDSP_DFT_zop_CreateSetupD Returns a setup structure that contains precalculated data for forward and inverse, complex, double-precision DFT functions. ``` vDSP_DFT_SetupDvDSP_DFT_zop_CreateSetupD(vDSP_DFT_SetupD __Previous, vDSP_Length __Length, vDSP_DFT_Direction __Direction); ``` ## Parameters `__Previous` An existing [`vDSP_DFT_SetupD`](/documentation/Accelerate/vDSP_DFT_SetupD) structure that shares memory with the returned setup structure. Pass `nil` to create an object with newly initialized and allocated memory. `__Length` The number of complex elements to process. The supported values are *f* * 2***n*, where *f* is 1, 3, 5, or 15 and *n* is at least 3. `__Direction` A flag that specifies the transform direction. Pass [`vDSP_DFT_Direction.FORWARD`](/documentation/Accelerate/vDSP_DFT_Direction/FORWARD) to transform from the time domain to the frequency domain. Pass [`vDSP_DFT_Direction.INVERSE`](/documentation/Accelerate/vDSP_DFT_Direction/INVERSE) to transform from the frequency domain to the time domain. ## Return Value Returns a [`vDSP_DFT_SetupD`](/documentation/Accelerate/vDSP_DFT_SetupD) object, or `nil` if the function fails, either from insufficient memory or because `Length` doesn’t satisfy the requirements given above. ## Discussion> Important: > To prevent potential memory leaks, if the `Previous` parameter is not `nil`, the return value and the `Previous` value must be different variables. ## Discussion This function shares memory between data structures where possible. If you have an existing setup object, you should pass that object as `Previous`. By doing so, the returned setup object can share underlying data storage with that object. Note that this function may allocate memory; you can free any allocated memory by calling [`vDSP_DFT_DestroySetupD`](/documentation/Accelerate/vDSP_DFT_DestroySetupD). ### Using shared setup objects If you’re using a shared setup object, the subsequent execute function requires that the input and output pointers are 64-byte aligned. The following code shows how to create the correctly aligned vectors: ```swift double* reals = (double*)aligned_alloc(64, length*sizeof(double)); double* imaginaries = (double*)aligned_alloc(64, length*sizeof(double)); ``` ## See Also --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)