Converts a per-chromosome interval set to indexed format (intervals.dat + intervals.idx) which reduces file descriptor usage.
Details
The indexed format stores all chromosomes in a single intervals.dat file with an intervals.idx index file. This reduces file descriptor usage from N files (one per chromosome) to just 2 files.
The conversion process:
Creates temporary intervals.dat.tmp and intervals.idx.tmp files
Concatenates all per-chromosome files into intervals.dat.tmp
Builds index with offsets and checksums
Atomically renames temporary files to final names
Optionally removes old per-chromosome files
The indexed format is 100