This is makeindex, version 2.15 [TeX Live 2019] (kpathsea + Thai support).
Scanning input file refman.idx........done (4546 entries accepted, 0 rejected).
Sorting entries............................................done (61417 comparisons).
Generating output file refman.ind........done (7325 lines written, 0 warnings).
Output written in refman.ind.
Transcript written in refman.ilg.