strbuf_getwholeline: avoid calling strbuf_grow
As with the recent speedup to strbuf_addch, we can avoid calling strbuf_grow() in a tight loop of single-character adds by instead checking strbuf_avail. Note that we would instead call strbuf_addch directly here, but it does more work than necessary: it will NUL-terminate the result for each character read. Instead, in this loop we read the characters one by one and then add the terminator manually at the end. Running "git rev-parse refs/heads/does-not-exist" on a repo with an extremely large (1.6GB) packed-refs file went from (best-of-5): real 0m10.948s user 0m10.548s sys 0m0.412s to: real 0m8.601s user 0m8.084s sys 0m0.524s for a wall-clock speedup of 21%. Helped-by: NEric Sunshine <sunshine@sunshineco.com> Signed-off-by: NJeff King <peff@peff.net> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
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