Thanks, I got it. The main trick is the standard "interview" trick of writing from right to left.

I'm not sure your solution work though without memory moving, because in your second step if the values of A are larger than the values of C, the growing B will hit the non decreasing set A.

To convince my self, I wrote for myself the following sequence.

00000224446666666666888888_11133333355555

BytesOfTheCompressedStream_NewSortedChunk________________

BytesOfTheCompressedStream_NewSortedChunk________weNsetyB

OfTheCompressedStream_SortedChunk________________weNsetyB

OfTheCompressedStream_SortedChunk________detroSfOweNsetyB

TheCompressedStream_Chunk________________detroSfOweNsetyB

TheCompressedStream_Chunk_______detroSehTdetroSfOweNsetyB

CompressedStream_Chunk__________detroSehTdetroSfOweNsetyB

Here notice that we hit the existing streams so we need to memmove

CompressedStream_Chunk_esserpmoCdetroSehTdetroSfOweNsetyB

dStream_Chunk__________esserpmoCdetroSehTdetroSfOweNsetyB

dStream_Chunk____knuhCdesserpmoCdetroSehTdetroSfOweNsetyB

Stream_____maertSknuhCdesserpmoCdetroSehTdetroSfOweNsetyB

___________maertSknuhCdesserpmoCdetroSehTdetroSfOweNsetyB

Then reverse it in place and memmove