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authorVicent Marti <tanoku@gmail.com>2013-11-14 12:43:51 (GMT)
committerJunio C Hamano <gitster@pobox.com>2013-12-30 20:17:20 (GMT)
commite1273106f62927e3efdb1cfa107cb1a9f913274c (patch)
tree9a23af0dbec1791e1a0d8b3137e614744ee14f19 /ewah/bitmap.c
parent7e3dae494370b5596a6ea76af1191829ce11bce2 (diff)
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ewah: compressed bitmap implementation
EWAH is a word-aligned compressed variant of a bitset (i.e. a data structure that acts as a 0-indexed boolean array for many entries). It uses a 64-bit run-length encoding (RLE) compression scheme, trading some compression for better processing speed. The goal of this word-aligned implementation is not to achieve the best compression, but rather to improve query processing time. As it stands right now, this EWAH implementation will always be more efficient storage-wise than its uncompressed alternative. EWAH arrays will be used as the on-disk format to store reachability bitmaps for all objects in a repository while keeping reasonable sizes, in the same way that JGit does. This EWAH implementation is a mostly straightforward port of the original `javaewah` library that JGit currently uses. The library is self-contained and has been embedded whole (4 files) inside the `ewah` folder to ease redistribution. The library is re-licensed under the GPLv2 with the permission of Daniel Lemire, the original author. The source code for the C version can be found on GitHub: https://github.com/vmg/libewok The original Java implementation can also be found on GitHub: https://github.com/lemire/javaewah [jc: stripped debug-only code per Peff's $gmane/239768] Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Helped-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'ewah/bitmap.c')
-rw-r--r--ewah/bitmap.c221
1 files changed, 221 insertions, 0 deletions
diff --git a/ewah/bitmap.c b/ewah/bitmap.c
new file mode 100644
index 0000000..710e58c
--- /dev/null
+++ b/ewah/bitmap.c
@@ -0,0 +1,221 @@
+/**
+ * Copyright 2013, GitHub, Inc
+ * Copyright 2009-2013, Daniel Lemire, Cliff Moon,
+ * David McIntosh, Robert Becho, Google Inc. and Veronika Zenz
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+#include "git-compat-util.h"
+#include "ewok.h"
+
+#define MASK(x) ((eword_t)1 << (x % BITS_IN_WORD))
+#define BLOCK(x) (x / BITS_IN_WORD)
+
+struct bitmap *bitmap_new(void)
+{
+ struct bitmap *bitmap = ewah_malloc(sizeof(struct bitmap));
+ bitmap->words = ewah_calloc(32, sizeof(eword_t));
+ bitmap->word_alloc = 32;
+ return bitmap;
+}
+
+void bitmap_set(struct bitmap *self, size_t pos)
+{
+ size_t block = BLOCK(pos);
+
+ if (block >= self->word_alloc) {
+ size_t old_size = self->word_alloc;
+ self->word_alloc = block * 2;
+ self->words = ewah_realloc(self->words,
+ self->word_alloc * sizeof(eword_t));
+
+ memset(self->words + old_size, 0x0,
+ (self->word_alloc - old_size) * sizeof(eword_t));
+ }
+
+ self->words[block] |= MASK(pos);
+}
+
+void bitmap_clear(struct bitmap *self, size_t pos)
+{
+ size_t block = BLOCK(pos);
+
+ if (block < self->word_alloc)
+ self->words[block] &= ~MASK(pos);
+}
+
+int bitmap_get(struct bitmap *self, size_t pos)
+{
+ size_t block = BLOCK(pos);
+ return block < self->word_alloc &&
+ (self->words[block] & MASK(pos)) != 0;
+}
+
+struct ewah_bitmap *bitmap_to_ewah(struct bitmap *bitmap)
+{
+ struct ewah_bitmap *ewah = ewah_new();
+ size_t i, running_empty_words = 0;
+ eword_t last_word = 0;
+
+ for (i = 0; i < bitmap->word_alloc; ++i) {
+ if (bitmap->words[i] == 0) {
+ running_empty_words++;
+ continue;
+ }
+
+ if (last_word != 0)
+ ewah_add(ewah, last_word);
+
+ if (running_empty_words > 0) {
+ ewah_add_empty_words(ewah, 0, running_empty_words);
+ running_empty_words = 0;
+ }
+
+ last_word = bitmap->words[i];
+ }
+
+ ewah_add(ewah, last_word);
+ return ewah;
+}
+
+struct bitmap *ewah_to_bitmap(struct ewah_bitmap *ewah)
+{
+ struct bitmap *bitmap = bitmap_new();
+ struct ewah_iterator it;
+ eword_t blowup;
+ size_t i = 0;
+
+ ewah_iterator_init(&it, ewah);
+
+ while (ewah_iterator_next(&blowup, &it)) {
+ if (i >= bitmap->word_alloc) {
+ bitmap->word_alloc *= 1.5;
+ bitmap->words = ewah_realloc(
+ bitmap->words, bitmap->word_alloc * sizeof(eword_t));
+ }
+
+ bitmap->words[i++] = blowup;
+ }
+
+ bitmap->word_alloc = i;
+ return bitmap;
+}
+
+void bitmap_and_not(struct bitmap *self, struct bitmap *other)
+{
+ const size_t count = (self->word_alloc < other->word_alloc) ?
+ self->word_alloc : other->word_alloc;
+
+ size_t i;
+
+ for (i = 0; i < count; ++i)
+ self->words[i] &= ~other->words[i];
+}
+
+void bitmap_or_ewah(struct bitmap *self, struct ewah_bitmap *other)
+{
+ size_t original_size = self->word_alloc;
+ size_t other_final = (other->bit_size / BITS_IN_WORD) + 1;
+ size_t i = 0;
+ struct ewah_iterator it;
+ eword_t word;
+
+ if (self->word_alloc < other_final) {
+ self->word_alloc = other_final;
+ self->words = ewah_realloc(self->words,
+ self->word_alloc * sizeof(eword_t));
+ memset(self->words + original_size, 0x0,
+ (self->word_alloc - original_size) * sizeof(eword_t));
+ }
+
+ ewah_iterator_init(&it, other);
+
+ while (ewah_iterator_next(&word, &it))
+ self->words[i++] |= word;
+}
+
+void bitmap_each_bit(struct bitmap *self, ewah_callback callback, void *data)
+{
+ size_t pos = 0, i;
+
+ for (i = 0; i < self->word_alloc; ++i) {
+ eword_t word = self->words[i];
+ uint32_t offset;
+
+ if (word == (eword_t)~0) {
+ for (offset = 0; offset < BITS_IN_WORD; ++offset)
+ callback(pos++, data);
+ } else {
+ for (offset = 0; offset < BITS_IN_WORD; ++offset) {
+ if ((word >> offset) == 0)
+ break;
+
+ offset += ewah_bit_ctz64(word >> offset);
+ callback(pos + offset, data);
+ }
+ pos += BITS_IN_WORD;
+ }
+ }
+}
+
+size_t bitmap_popcount(struct bitmap *self)
+{
+ size_t i, count = 0;
+
+ for (i = 0; i < self->word_alloc; ++i)
+ count += ewah_bit_popcount64(self->words[i]);
+
+ return count;
+}
+
+int bitmap_equals(struct bitmap *self, struct bitmap *other)
+{
+ struct bitmap *big, *small;
+ size_t i;
+
+ if (self->word_alloc < other->word_alloc) {
+ small = self;
+ big = other;
+ } else {
+ small = other;
+ big = self;
+ }
+
+ for (i = 0; i < small->word_alloc; ++i) {
+ if (small->words[i] != big->words[i])
+ return 0;
+ }
+
+ for (; i < big->word_alloc; ++i) {
+ if (big->words[i] != 0)
+ return 0;
+ }
+
+ return 1;
+}
+
+void bitmap_reset(struct bitmap *bitmap)
+{
+ memset(bitmap->words, 0x0, bitmap->word_alloc * sizeof(eword_t));
+}
+
+void bitmap_free(struct bitmap *bitmap)
+{
+ if (bitmap == NULL)
+ return;
+
+ free(bitmap->words);
+ free(bitmap);
+}