Comment in DCT4 allowed length
* Note that the implementation of Inverse DCT4 and DCT4 is same, hence same process function can be used for both.
*
* \par Lengths supported by the transform:
- * As DCT4 internally uses Real FFT, it supports all the lengths supported by arm_rfft_f32().
+ * As DCT4 internally uses Real FFT, it supports all the lengths 128, 512, 2048 and 8192.
* The library provides separate functions for Q15, Q31, and floating-point data types.
* \par Instance Structure
* The instances for Real FFT and FFT, cosine values table and twiddle factor table are stored in an instance data structure.
