This is makeindex, version 2.17 [TeX Live 2023] (kpathsea + Thai support).
Scanning input file refman.idx.....done (1609 entries accepted, 0 rejected).
Sorting entries................done (19095 comparisons).
Generating output file refman.ind.....done (1833 lines written, 0 warnings).
Output written in refman.ind.
Transcript written in refman.ilg.