This is makeindex, version 2.17 [TeX Live 2023] (kpathsea + Thai support).
Scanning input file refman.idx....done (183 entries accepted, 0 rejected).
Sorting entries....done (1457 comparisons).
Generating output file refman.ind....done (313 lines written, 0 warnings).
Output written in refman.ind.
Transcript written in refman.ilg.