add a hashtable implementation that supports O(1) removal

The existing hashtable implementation (in hash.[ch]) uses open addressing
(i.e. resolve hash collisions by distributing entries across the table).
Thus, removal is difficult to implement with less than O(n) complexity.
Resolving collisions of entries with identical hashes (e.g. via chaining)
is left to the client code.

Add a hashtable implementation that supports O(1) removal and is slightly
easier to use due to builtin entry chaining.

Supports all basic operations init, free, get, add, remove and iteration.

Also includes ready-to-use hash functions based on the public domain FNV-1
algorithm (http://www.isthe.com/chongo/tech/comp/fnv).

The per-entry data structure (hashmap_entry) is piggybacked in front of
the client's data structure to save memory. See test-hashmap.c for usage
examples.

The hashtable is resized by a factor of four when 80% full. With these
settings, average memory consumption is about 2/3 of hash.[ch], and
insertion is about twice as fast due to less frequent resizing.

Lookups are also slightly faster, because entries are strictly confined to
their bucket (i.e. no data of other buckets needs to be traversed).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 240 insertions, 0 deletions

diff --git a/t/t0011-hashmap.sh b/t/t0011-hashmap.sh
new file mode 100755
index 000000000..391e2b649
--- /dev/null
+++ b/t/t0011-hashmap.sh
@@ -0,0 +1,240 @@
+#!/bin/sh
+
+test_description='test hashmap and string hash functions'
+. ./test-lib.sh
+
+test_hashmap() {
+	echo "$1" | test-hashmap $3 > actual &&
+	echo "$2" > expect &&
+	test_cmp expect actual
+}
+
+test_expect_success 'hash functions' '
+
+test_hashmap "hash key1" "2215982743 2215982743 116372151 116372151" &&
+test_hashmap "hash key2" "2215982740 2215982740 116372148 116372148" &&
+test_hashmap "hash fooBarFrotz" "1383912807 1383912807 3189766727 3189766727" &&
+test_hashmap "hash foobarfrotz" "2862305959 2862305959 3189766727 3189766727"
+
+'
+
+test_expect_success 'put' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+put foobarfrotz value4
+size" "NULL
+NULL
+NULL
+NULL
+64 4"
+
+'
+
+test_expect_success 'put (case insensitive)' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+size" "NULL
+NULL
+NULL
+64 3" ignorecase
+
+'
+
+test_expect_success 'replace' '
+
+test_hashmap "put key1 value1
+put key1 value2
+put fooBarFrotz value3
+put fooBarFrotz value4
+size" "NULL
+value1
+NULL
+value3
+64 2"
+
+'
+
+test_expect_success 'replace (case insensitive)' '
+
+test_hashmap "put key1 value1
+put Key1 value2
+put fooBarFrotz value3
+put foobarfrotz value4
+size" "NULL
+value1
+NULL
+value3
+64 2" ignorecase
+
+'
+
+test_expect_success 'get' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+put foobarfrotz value4
+get key1
+get key2
+get fooBarFrotz
+get notInMap" "NULL
+NULL
+NULL
+NULL
+value1
+value2
+value3
+NULL"
+
+'
+
+test_expect_success 'get (case insensitive)' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+get Key1
+get keY2
+get foobarfrotz
+get notInMap" "NULL
+NULL
+NULL
+value1
+value2
+value3
+NULL" ignorecase
+
+'
+
+test_expect_success 'add' '
+
+test_hashmap "add key1 value1
+add key1 value2
+add fooBarFrotz value3
+add fooBarFrotz value4
+get key1
+get fooBarFrotz
+get notInMap" "value2
+value1
+value4
+value3
+NULL"
+
+'
+
+test_expect_success 'add (case insensitive)' '
+
+test_hashmap "add key1 value1
+add Key1 value2
+add fooBarFrotz value3
+add foobarfrotz value4
+get key1
+get Foobarfrotz
+get notInMap" "value2
+value1
+value4
+value3
+NULL" ignorecase
+
+'
+
+test_expect_success 'remove' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+remove key1
+remove key2
+remove notInMap
+size" "NULL
+NULL
+NULL
+value1
+value2
+NULL
+64 1"
+
+'
+
+test_expect_success 'remove (case insensitive)' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+remove Key1
+remove keY2
+remove notInMap
+size" "NULL
+NULL
+NULL
+value1
+value2
+NULL
+64 1" ignorecase
+
+'
+
+test_expect_success 'iterate' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+iterate" "NULL
+NULL
+NULL
+key2 value2
+key1 value1
+fooBarFrotz value3"
+
+'
+
+test_expect_success 'iterate (case insensitive)' '
+
+test_hashmap "put key1 value1
+put key2 value2
+put fooBarFrotz value3
+iterate" "NULL
+NULL
+NULL
+fooBarFrotz value3
+key2 value2
+key1 value1" ignorecase
+
+'
+
+test_expect_success 'grow / shrink' '
+
+	rm -f in &&
+	rm -f expect &&
+	for n in $(test_seq 51)
+	do
+		echo put key$n value$n >> in &&
+		echo NULL >> expect
+	done &&
+	echo size >> in &&
+	echo 64 51 >> expect &&
+	echo put key52 value52 >> in &&
+	echo NULL >> expect
+	echo size >> in &&
+	echo 256 52 >> expect &&
+	for n in $(test_seq 12)
+	do
+		echo remove key$n >> in &&
+		echo value$n >> expect
+	done &&
+	echo size >> in &&
+	echo 256 40 >> expect &&
+	echo remove key40 >> in &&
+	echo value40 >> expect &&
+	echo size >> in &&
+	echo 64 39 >> expect &&
+	cat in | test-hashmap > out &&
+	test_cmp expect out
+
+'
+
+test_done