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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)
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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>
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+/**
+ * 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.
+ */
+#ifndef __EWOK_BITMAP_H__
+#define __EWOK_BITMAP_H__
+
+#ifndef ewah_malloc
+# define ewah_malloc xmalloc
+#endif
+#ifndef ewah_realloc
+# define ewah_realloc xrealloc
+#endif
+#ifndef ewah_calloc
+# define ewah_calloc xcalloc
+#endif
+
+typedef uint64_t eword_t;
+#define BITS_IN_WORD (sizeof(eword_t) * 8)
+
+/**
+ * Do not use __builtin_popcountll. The GCC implementation
+ * is notoriously slow on all platforms.
+ *
+ * See: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36041
+ */
+static inline uint32_t ewah_bit_popcount64(uint64_t x)
+{
+ x = (x & 0x5555555555555555ULL) + ((x >> 1) & 0x5555555555555555ULL);
+ x = (x & 0x3333333333333333ULL) + ((x >> 2) & 0x3333333333333333ULL);
+ x = (x & 0x0F0F0F0F0F0F0F0FULL) + ((x >> 4) & 0x0F0F0F0F0F0F0F0FULL);
+ return (x * 0x0101010101010101ULL) >> 56;
+}
+
+#ifdef __GNUC__
+#define ewah_bit_ctz64(x) __builtin_ctzll(x)
+#else
+static inline int ewah_bit_ctz64(uint64_t x)
+{
+ int n = 0;
+ if ((x & 0xffffffff) == 0) { x >>= 32; n += 32; }
+ if ((x & 0xffff) == 0) { x >>= 16; n += 16; }
+ if ((x & 0xff) == 0) { x >>= 8; n += 8; }
+ if ((x & 0xf) == 0) { x >>= 4; n += 4; }
+ if ((x & 0x3) == 0) { x >>= 2; n += 2; }
+ if ((x & 0x1) == 0) { x >>= 1; n += 1; }
+ return n + !x;
+}
+#endif
+
+struct ewah_bitmap {
+ eword_t *buffer;
+ size_t buffer_size;
+ size_t alloc_size;
+ size_t bit_size;
+ eword_t *rlw;
+};
+
+typedef void (*ewah_callback)(size_t pos, void *);
+
+struct ewah_bitmap *ewah_pool_new(void);
+void ewah_pool_free(struct ewah_bitmap *self);
+
+/**
+ * Allocate a new EWAH Compressed bitmap
+ */
+struct ewah_bitmap *ewah_new(void);
+
+/**
+ * Clear all the bits in the bitmap. Does not free or resize
+ * memory.
+ */
+void ewah_clear(struct ewah_bitmap *self);
+
+/**
+ * Free all the memory of the bitmap
+ */
+void ewah_free(struct ewah_bitmap *self);
+
+int ewah_serialize_to(struct ewah_bitmap *self,
+ int (*write_fun)(void *out, const void *buf, size_t len),
+ void *out);
+int ewah_serialize(struct ewah_bitmap *self, int fd);
+int ewah_serialize_native(struct ewah_bitmap *self, int fd);
+
+int ewah_deserialize(struct ewah_bitmap *self, int fd);
+int ewah_read_mmap(struct ewah_bitmap *self, void *map, size_t len);
+int ewah_read_mmap_native(struct ewah_bitmap *self, void *map, size_t len);
+
+uint32_t ewah_checksum(struct ewah_bitmap *self);
+
+/**
+ * Logical not (bitwise negation) in-place on the bitmap
+ *
+ * This operation is linear time based on the size of the bitmap.
+ */
+void ewah_not(struct ewah_bitmap *self);
+
+/**
+ * Call the given callback with the position of every single bit
+ * that has been set on the bitmap.
+ *
+ * This is an efficient operation that does not fully decompress
+ * the bitmap.
+ */
+void ewah_each_bit(struct ewah_bitmap *self, ewah_callback callback, void *payload);
+
+/**
+ * Set a given bit on the bitmap.
+ *
+ * The bit at position `pos` will be set to true. Because of the
+ * way that the bitmap is compressed, a set bit cannot be unset
+ * later on.
+ *
+ * Furthermore, since the bitmap uses streaming compression, bits
+ * can only set incrementally.
+ *
+ * E.g.
+ * ewah_set(bitmap, 1); // ok
+ * ewah_set(bitmap, 76); // ok
+ * ewah_set(bitmap, 77); // ok
+ * ewah_set(bitmap, 8712800127); // ok
+ * ewah_set(bitmap, 25); // failed, assert raised
+ */
+void ewah_set(struct ewah_bitmap *self, size_t i);
+
+struct ewah_iterator {
+ const eword_t *buffer;
+ size_t buffer_size;
+
+ size_t pointer;
+ eword_t compressed, literals;
+ eword_t rl, lw;
+ int b;
+};
+
+/**
+ * Initialize a new iterator to run through the bitmap in uncompressed form.
+ *
+ * The iterator can be stack allocated. The underlying bitmap must not be freed
+ * before the iteration is over.
+ *
+ * E.g.
+ *
+ * struct ewah_bitmap *bitmap = ewah_new();
+ * struct ewah_iterator it;
+ *
+ * ewah_iterator_init(&it, bitmap);
+ */
+void ewah_iterator_init(struct ewah_iterator *it, struct ewah_bitmap *parent);
+
+/**
+ * Yield every single word in the bitmap in uncompressed form. This is:
+ * yield single words (32-64 bits) where each bit represents an actual
+ * bit from the bitmap.
+ *
+ * Return: true if a word was yield, false if there are no words left
+ */
+int ewah_iterator_next(eword_t *next, struct ewah_iterator *it);
+
+void ewah_or(
+ struct ewah_bitmap *ewah_i,
+ struct ewah_bitmap *ewah_j,
+ struct ewah_bitmap *out);
+
+void ewah_and_not(
+ struct ewah_bitmap *ewah_i,
+ struct ewah_bitmap *ewah_j,
+ struct ewah_bitmap *out);
+
+void ewah_xor(
+ struct ewah_bitmap *ewah_i,
+ struct ewah_bitmap *ewah_j,
+ struct ewah_bitmap *out);
+
+void ewah_and(
+ struct ewah_bitmap *ewah_i,
+ struct ewah_bitmap *ewah_j,
+ struct ewah_bitmap *out);
+
+/**
+ * Direct word access
+ */
+size_t ewah_add_empty_words(struct ewah_bitmap *self, int v, size_t number);
+void ewah_add_dirty_words(
+ struct ewah_bitmap *self, const eword_t *buffer, size_t number, int negate);
+size_t ewah_add(struct ewah_bitmap *self, eword_t word);
+
+
+/**
+ * Uncompressed, old-school bitmap that can be efficiently compressed
+ * into an `ewah_bitmap`.
+ */
+struct bitmap {
+ eword_t *words;
+ size_t word_alloc;
+};
+
+struct bitmap *bitmap_new(void);
+void bitmap_set(struct bitmap *self, size_t pos);
+void bitmap_clear(struct bitmap *self, size_t pos);
+int bitmap_get(struct bitmap *self, size_t pos);
+void bitmap_reset(struct bitmap *self);
+void bitmap_free(struct bitmap *self);
+int bitmap_equals(struct bitmap *self, struct bitmap *other);
+int bitmap_is_subset(struct bitmap *self, struct bitmap *super);
+
+struct ewah_bitmap * bitmap_to_ewah(struct bitmap *bitmap);
+struct bitmap *ewah_to_bitmap(struct ewah_bitmap *ewah);
+
+void bitmap_and_not(struct bitmap *self, struct bitmap *other);
+void bitmap_or_ewah(struct bitmap *self, struct ewah_bitmap *other);
+void bitmap_or(struct bitmap *self, const struct bitmap *other);
+
+void bitmap_each_bit(struct bitmap *self, ewah_callback callback, void *data);
+size_t bitmap_popcount(struct bitmap *self);
+
+#endif