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>

René Scharfe committed Feb 4, 2020 at 22:24 UTC 1c56fc208400011b196f571041a0bc694fc9637c

1 file changed +14 -6

builtin/name-rev.c

+14 -6

@@ -103,15 +103,23 @@ static struct rev_name *create_or_update_name(struct commit *commit,

103

104 static char *get_parent_name(const struct rev_name *name, int parent_number)

105 {

106 + struct strbuf sb = STRBUF_INIT;

107 size_t len;

108

109 strip_suffix(name->tip_name, "^0", &len);

109 - if (name->generation > 0)

110 - return xstrfmt("%.*s~%d^%d", (int)len, name->tip_name,

111 - name->generation, parent_number);

112 - else

113 - return xstrfmt("%.*s^%d", (int)len, name->tip_name,

114 - parent_number);

110 + if (name->generation > 0) {

111 + strbuf_grow(&sb, len +

112 + 1 + decimal_width(name->generation) +

113 + 1 + decimal_width(parent_number));

114 + strbuf_addf(&sb, "%.*s~%d^%d", (int)len, name->tip_name,

115 + name->generation, parent_number);

116 + } else {

117 + strbuf_grow(&sb, len +

118 + 1 + decimal_width(parent_number));

119 + strbuf_addf(&sb, "%.*s^%d", (int)len, name->tip_name,

120 + parent_number);

121 + }

122 + return strbuf_detach(&sb, NULL);

123 }

124

125 static void name_rev(struct commit *start_commit,