6 files changed, 87 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index 6f5986b66e..65403f6dd0 100644
--- a/Makefile
+++ b/Makefile
@@ -816,6 +816,7 @@ TEST_BUILTINS_OBJS += test-lazy-init-name-hash.o
 TEST_BUILTINS_OBJS += test-match-trees.o
 TEST_BUILTINS_OBJS += test-mergesort.o
 TEST_BUILTINS_OBJS += test-mktemp.o
+TEST_BUILTINS_OBJS += test-name-hash.o
 TEST_BUILTINS_OBJS += test-online-cpus.o
 TEST_BUILTINS_OBJS += test-pack-mtimes.o
 TEST_BUILTINS_OBJS += test-parse-options.o
diff --git a/t/helper/test-name-hash.c b/t/helper/test-name-hash.c
new file mode 100644
index 0000000000..af1d52de10
--- /dev/null
+++ b/t/helper/test-name-hash.c
@@ -0,0 +1,23 @@
+/*
+ * test-name-hash.c: Read a list of paths over stdin and report on their
+ * name-hash and full name-hash.
+ */
+
+#include "test-tool.h"
+#include "git-compat-util.h"
+#include "pack-objects.h"
+#include "strbuf.h"
+
+int cmd__name_hash(int argc UNUSED, const char **argv UNUSED)
+{
+	struct strbuf line = STRBUF_INIT;
+
+	while (!strbuf_getline(&line, stdin)) {
+		printf("%10u ", pack_name_hash(line.buf));
+		printf("%10u ", pack_name_hash_v2((unsigned const char *)line.buf));
+		printf("%s\n", line.buf);
+	}
+
+	strbuf_release(&line);
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 1ebb69a5dc..e794058ab6 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -44,6 +44,7 @@ static struct test_cmd cmds[] = {
 	{ "match-trees", cmd__match_trees },
 	{ "mergesort", cmd__mergesort },
 	{ "mktemp", cmd__mktemp },
+	{ "name-hash", cmd__name_hash },
 	{ "online-cpus", cmd__online_cpus },
 	{ "pack-mtimes", cmd__pack_mtimes },
 	{ "parse-options", cmd__parse_options },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 21802ac27d..26ff30a5a9 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -37,6 +37,7 @@ int cmd__lazy_init_name_hash(int argc, const char **argv);
 int cmd__match_trees(int argc, const char **argv);
 int cmd__mergesort(int argc, const char **argv);
 int cmd__mktemp(int argc, const char **argv);
+int cmd__name_hash(int argc, const char **argv);
 int cmd__online_cpus(int argc, const char **argv);
 int cmd__pack_mtimes(int argc, const char **argv);
 int cmd__parse_options(int argc, const char **argv);
diff --git a/t/perf/p5314-name-hash.sh b/t/perf/p5314-name-hash.sh
new file mode 100755
index 0000000000..4ef0ba7711
--- /dev/null
+++ b/t/perf/p5314-name-hash.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+
+test_description='Tests pack performance using bitmaps'
+. ./perf-lib.sh
+
+GIT_TEST_PASSING_SANITIZE_LEAK=0
+export GIT_TEST_PASSING_SANITIZE_LEAK
+
+test_perf_large_repo
+
+test_size 'paths at head' '
+	git ls-tree -r --name-only HEAD >path-list &&
+	wc -l <path-list &&
+	test-tool name-hash <path-list >name-hashes
+'
+
+for version in 1 2
+do
+	test_size "distinct hash value: v$version" '
+		awk "{ print \$$version; }" <name-hashes | sort | \
+			uniq -c >name-hash-count &&
+		wc -l <name-hash-count
+	'
+
+	test_size "maximum multiplicity: v$version" '
+		sort -nr <name-hash-count | head -n 1 |	\
+			awk "{ print \$1; }"
+	'
+done
+
+test_done
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index c30522b57f..871ce01401 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -27,6 +27,36 @@ has_any () {
 	grep -Ff "$1" "$2"
 }
 
+# Since name-hash values are stored in the .bitmap files, add a test
+# that checks that the name-hash calculations are stable across versions.
+# Not exhaustive, but these hashing algorithms would be hard to change
+# without causing deviations here.
+test_expect_success 'name-hash value stability' '
+	cat >names <<-\EOF &&
+	first
+	second
+	third
+	a/one-long-enough-for-collisions
+	b/two-long-enough-for-collisions
+	many/parts/to/this/path/enough/to/collide/in/v2
+	enough/parts/to/this/path/enough/to/collide/in/v2
+	EOF
+
+	test-tool name-hash <names >out &&
+
+	cat >expect <<-\EOF &&
+	2582249472 1763573760 first
+	2289942528 1188134912 second
+	2300837888 1130758144 third
+	2544516325 3963087891 a/one-long-enough-for-collisions
+	2544516325 4013419539 b/two-long-enough-for-collisions
+	1420111091 1709547268 many/parts/to/this/path/enough/to/collide/in/v2
+	1420111091 1709547268 enough/parts/to/this/path/enough/to/collide/in/v2
+	EOF
+
+	test_cmp expect out
+'
+
 test_bitmap_cases () {
 	writeLookupTable=false
 	for i in "$@"