What do you call as lossless JPEG rotation? If that is technique used in IJG library than it is not mathematically lossless and is not necessary faster then just full decode and rotate.
What widely called as JPEG lossless rotate is partial decoding up to final up-sampling and color conversion steps, that is:
1. huffman decode of DCT coefficients 2. dequantization 3. inverse DCT transform (which brings data from frequency domain back to time domain and produceimage pixels) - here is the point where it is possible to rotatepixel data before the final step, which is up-sampling (if needed) and color conversion (if needed)
First, the only mathematically lossless operation here is huffman decoding. Second, performance of IPP implementation of up-sampling and color-conversion functions reduce difference in time required to that "lossless rotate operation" and just naive full decoding and rotate.