name-rev: pre-size buffer in get_parent_name()
We can calculate the size of new name easily and precisely. Open-code
the xstrfmt() calls and grow the buffers as needed before filling them.
This provides a surprisingly large benefit when working with the
Chromium repository; here are the numbers measured using hyperfine
before:
Benchmark #1: ./git -C ../chromium/src name-rev --all
Time (mean ± σ): 5.822 s ± 0.013 s [User: 5.304 s, System: 0.516 s]
Range (min … max): 5.803 s … 5.837 s 10 runs
... and with this patch:
Benchmark #1: ./git -C ../chromium/src name-rev --all
Time (mean ± σ): 1.527 s ± 0.003 s [User: 1.015 s, System: 0.511 s]
Range (min … max): 1.524 s … 1.535 s 10 runs
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>