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replace adler32 with Rabin's polynomial in diff-delta
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This brings another small repacking speedup for sensibly the same pack
size.  On the Linux kernel repo, git-repack -a -f is 3.7% faster for a
0.4% larger pack.

Credits to Geert Bosch who brought the Rabin's polynomial idea to my
attention.

This also eliminate the issue of adler32() reading past the data buffer,
as noticed by Johannes Schindelin.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
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Nicolas Pitre authored and Junio C Hamano committed Apr 29, 2006
1 parent f6c7081 commit 3dc5a9e
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2 changes: 1 addition & 1 deletion Makefile
Original file line number Diff line number Diff line change
Expand Up @@ -609,7 +609,7 @@ test-date$X: test-date.c date.o ctype.o
$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) test-date.c date.o ctype.o

test-delta$X: test-delta.c diff-delta.o patch-delta.o
$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $^ -lz
$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $^

check:
for i in *.c; do sparse $(ALL_CFLAGS) $(SPARSE_FLAGS) $$i || exit; done
Expand Down
184 changes: 150 additions & 34 deletions diff-delta.c
Original file line number Diff line number Diff line change
Expand Up @@ -20,18 +20,106 @@

#include <stdlib.h>
#include <string.h>
#include <zlib.h>
#include "delta.h"


/* block size: min = 16, max = 64k, power of 2 */
#define BLK_SIZE 16

/* maximum hash entry list for the same hash bucket */
#define HASH_LIMIT 64

#define GR_PRIME 0x9e370001
#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
#define RABIN_SHIFT 23
#define RABIN_WINDOW 16

static const unsigned int T[256] = {
0x00000000, 0xab59b4d1, 0x56b369a2, 0xfdeadd73, 0x063f6795, 0xad66d344,
0x508c0e37, 0xfbd5bae6, 0x0c7ecf2a, 0xa7277bfb, 0x5acda688, 0xf1941259,
0x0a41a8bf, 0xa1181c6e, 0x5cf2c11d, 0xf7ab75cc, 0x18fd9e54, 0xb3a42a85,
0x4e4ef7f6, 0xe5174327, 0x1ec2f9c1, 0xb59b4d10, 0x48719063, 0xe32824b2,
0x1483517e, 0xbfdae5af, 0x423038dc, 0xe9698c0d, 0x12bc36eb, 0xb9e5823a,
0x440f5f49, 0xef56eb98, 0x31fb3ca8, 0x9aa28879, 0x6748550a, 0xcc11e1db,
0x37c45b3d, 0x9c9defec, 0x6177329f, 0xca2e864e, 0x3d85f382, 0x96dc4753,
0x6b369a20, 0xc06f2ef1, 0x3bba9417, 0x90e320c6, 0x6d09fdb5, 0xc6504964,
0x2906a2fc, 0x825f162d, 0x7fb5cb5e, 0xd4ec7f8f, 0x2f39c569, 0x846071b8,
0x798aaccb, 0xd2d3181a, 0x25786dd6, 0x8e21d907, 0x73cb0474, 0xd892b0a5,
0x23470a43, 0x881ebe92, 0x75f463e1, 0xdeadd730, 0x63f67950, 0xc8afcd81,
0x354510f2, 0x9e1ca423, 0x65c91ec5, 0xce90aa14, 0x337a7767, 0x9823c3b6,
0x6f88b67a, 0xc4d102ab, 0x393bdfd8, 0x92626b09, 0x69b7d1ef, 0xc2ee653e,
0x3f04b84d, 0x945d0c9c, 0x7b0be704, 0xd05253d5, 0x2db88ea6, 0x86e13a77,
0x7d348091, 0xd66d3440, 0x2b87e933, 0x80de5de2, 0x7775282e, 0xdc2c9cff,
0x21c6418c, 0x8a9ff55d, 0x714a4fbb, 0xda13fb6a, 0x27f92619, 0x8ca092c8,
0x520d45f8, 0xf954f129, 0x04be2c5a, 0xafe7988b, 0x5432226d, 0xff6b96bc,
0x02814bcf, 0xa9d8ff1e, 0x5e738ad2, 0xf52a3e03, 0x08c0e370, 0xa39957a1,
0x584ced47, 0xf3155996, 0x0eff84e5, 0xa5a63034, 0x4af0dbac, 0xe1a96f7d,
0x1c43b20e, 0xb71a06df, 0x4ccfbc39, 0xe79608e8, 0x1a7cd59b, 0xb125614a,
0x468e1486, 0xedd7a057, 0x103d7d24, 0xbb64c9f5, 0x40b17313, 0xebe8c7c2,
0x16021ab1, 0xbd5bae60, 0x6cb54671, 0xc7ecf2a0, 0x3a062fd3, 0x915f9b02,
0x6a8a21e4, 0xc1d39535, 0x3c394846, 0x9760fc97, 0x60cb895b, 0xcb923d8a,
0x3678e0f9, 0x9d215428, 0x66f4eece, 0xcdad5a1f, 0x3047876c, 0x9b1e33bd,
0x7448d825, 0xdf116cf4, 0x22fbb187, 0x89a20556, 0x7277bfb0, 0xd92e0b61,
0x24c4d612, 0x8f9d62c3, 0x7836170f, 0xd36fa3de, 0x2e857ead, 0x85dcca7c,
0x7e09709a, 0xd550c44b, 0x28ba1938, 0x83e3ade9, 0x5d4e7ad9, 0xf617ce08,
0x0bfd137b, 0xa0a4a7aa, 0x5b711d4c, 0xf028a99d, 0x0dc274ee, 0xa69bc03f,
0x5130b5f3, 0xfa690122, 0x0783dc51, 0xacda6880, 0x570fd266, 0xfc5666b7,
0x01bcbbc4, 0xaae50f15, 0x45b3e48d, 0xeeea505c, 0x13008d2f, 0xb85939fe,
0x438c8318, 0xe8d537c9, 0x153feaba, 0xbe665e6b, 0x49cd2ba7, 0xe2949f76,
0x1f7e4205, 0xb427f6d4, 0x4ff24c32, 0xe4abf8e3, 0x19412590, 0xb2189141,
0x0f433f21, 0xa41a8bf0, 0x59f05683, 0xf2a9e252, 0x097c58b4, 0xa225ec65,
0x5fcf3116, 0xf49685c7, 0x033df00b, 0xa86444da, 0x558e99a9, 0xfed72d78,
0x0502979e, 0xae5b234f, 0x53b1fe3c, 0xf8e84aed, 0x17bea175, 0xbce715a4,
0x410dc8d7, 0xea547c06, 0x1181c6e0, 0xbad87231, 0x4732af42, 0xec6b1b93,
0x1bc06e5f, 0xb099da8e, 0x4d7307fd, 0xe62ab32c, 0x1dff09ca, 0xb6a6bd1b,
0x4b4c6068, 0xe015d4b9, 0x3eb80389, 0x95e1b758, 0x680b6a2b, 0xc352defa,
0x3887641c, 0x93ded0cd, 0x6e340dbe, 0xc56db96f, 0x32c6cca3, 0x999f7872,
0x6475a501, 0xcf2c11d0, 0x34f9ab36, 0x9fa01fe7, 0x624ac294, 0xc9137645,
0x26459ddd, 0x8d1c290c, 0x70f6f47f, 0xdbaf40ae, 0x207afa48, 0x8b234e99,
0x76c993ea, 0xdd90273b, 0x2a3b52f7, 0x8162e626, 0x7c883b55, 0xd7d18f84,
0x2c043562, 0x875d81b3, 0x7ab75cc0, 0xd1eee811
};

static const unsigned int U[256] = {
0x00000000, 0x7eb5200d, 0x5633f4cb, 0x2886d4c6, 0x073e5d47, 0x798b7d4a,
0x510da98c, 0x2fb88981, 0x0e7cba8e, 0x70c99a83, 0x584f4e45, 0x26fa6e48,
0x0942e7c9, 0x77f7c7c4, 0x5f711302, 0x21c4330f, 0x1cf9751c, 0x624c5511,
0x4aca81d7, 0x347fa1da, 0x1bc7285b, 0x65720856, 0x4df4dc90, 0x3341fc9d,
0x1285cf92, 0x6c30ef9f, 0x44b63b59, 0x3a031b54, 0x15bb92d5, 0x6b0eb2d8,
0x4388661e, 0x3d3d4613, 0x39f2ea38, 0x4747ca35, 0x6fc11ef3, 0x11743efe,
0x3eccb77f, 0x40799772, 0x68ff43b4, 0x164a63b9, 0x378e50b6, 0x493b70bb,
0x61bda47d, 0x1f088470, 0x30b00df1, 0x4e052dfc, 0x6683f93a, 0x1836d937,
0x250b9f24, 0x5bbebf29, 0x73386bef, 0x0d8d4be2, 0x2235c263, 0x5c80e26e,
0x740636a8, 0x0ab316a5, 0x2b7725aa, 0x55c205a7, 0x7d44d161, 0x03f1f16c,
0x2c4978ed, 0x52fc58e0, 0x7a7a8c26, 0x04cfac2b, 0x73e5d470, 0x0d50f47d,
0x25d620bb, 0x5b6300b6, 0x74db8937, 0x0a6ea93a, 0x22e87dfc, 0x5c5d5df1,
0x7d996efe, 0x032c4ef3, 0x2baa9a35, 0x551fba38, 0x7aa733b9, 0x041213b4,
0x2c94c772, 0x5221e77f, 0x6f1ca16c, 0x11a98161, 0x392f55a7, 0x479a75aa,
0x6822fc2b, 0x1697dc26, 0x3e1108e0, 0x40a428ed, 0x61601be2, 0x1fd53bef,
0x3753ef29, 0x49e6cf24, 0x665e46a5, 0x18eb66a8, 0x306db26e, 0x4ed89263,
0x4a173e48, 0x34a21e45, 0x1c24ca83, 0x6291ea8e, 0x4d29630f, 0x339c4302,
0x1b1a97c4, 0x65afb7c9, 0x446b84c6, 0x3adea4cb, 0x1258700d, 0x6ced5000,
0x4355d981, 0x3de0f98c, 0x15662d4a, 0x6bd30d47, 0x56ee4b54, 0x285b6b59,
0x00ddbf9f, 0x7e689f92, 0x51d01613, 0x2f65361e, 0x07e3e2d8, 0x7956c2d5,
0x5892f1da, 0x2627d1d7, 0x0ea10511, 0x7014251c, 0x5facac9d, 0x21198c90,
0x099f5856, 0x772a785b, 0x4c921c31, 0x32273c3c, 0x1aa1e8fa, 0x6414c8f7,
0x4bac4176, 0x3519617b, 0x1d9fb5bd, 0x632a95b0, 0x42eea6bf, 0x3c5b86b2,
0x14dd5274, 0x6a687279, 0x45d0fbf8, 0x3b65dbf5, 0x13e30f33, 0x6d562f3e,
0x506b692d, 0x2ede4920, 0x06589de6, 0x78edbdeb, 0x5755346a, 0x29e01467,
0x0166c0a1, 0x7fd3e0ac, 0x5e17d3a3, 0x20a2f3ae, 0x08242768, 0x76910765,
0x59298ee4, 0x279caee9, 0x0f1a7a2f, 0x71af5a22, 0x7560f609, 0x0bd5d604,
0x235302c2, 0x5de622cf, 0x725eab4e, 0x0ceb8b43, 0x246d5f85, 0x5ad87f88,
0x7b1c4c87, 0x05a96c8a, 0x2d2fb84c, 0x539a9841, 0x7c2211c0, 0x029731cd,
0x2a11e50b, 0x54a4c506, 0x69998315, 0x172ca318, 0x3faa77de, 0x411f57d3,
0x6ea7de52, 0x1012fe5f, 0x38942a99, 0x46210a94, 0x67e5399b, 0x19501996,
0x31d6cd50, 0x4f63ed5d, 0x60db64dc, 0x1e6e44d1, 0x36e89017, 0x485db01a,
0x3f77c841, 0x41c2e84c, 0x69443c8a, 0x17f11c87, 0x38499506, 0x46fcb50b,
0x6e7a61cd, 0x10cf41c0, 0x310b72cf, 0x4fbe52c2, 0x67388604, 0x198da609,
0x36352f88, 0x48800f85, 0x6006db43, 0x1eb3fb4e, 0x238ebd5d, 0x5d3b9d50,
0x75bd4996, 0x0b08699b, 0x24b0e01a, 0x5a05c017, 0x728314d1, 0x0c3634dc,
0x2df207d3, 0x534727de, 0x7bc1f318, 0x0574d315, 0x2acc5a94, 0x54797a99,
0x7cffae5f, 0x024a8e52, 0x06852279, 0x78300274, 0x50b6d6b2, 0x2e03f6bf,
0x01bb7f3e, 0x7f0e5f33, 0x57888bf5, 0x293dabf8, 0x08f998f7, 0x764cb8fa,
0x5eca6c3c, 0x207f4c31, 0x0fc7c5b0, 0x7172e5bd, 0x59f4317b, 0x27411176,
0x1a7c5765, 0x64c97768, 0x4c4fa3ae, 0x32fa83a3, 0x1d420a22, 0x63f72a2f,
0x4b71fee9, 0x35c4dee4, 0x1400edeb, 0x6ab5cde6, 0x42331920, 0x3c86392d,
0x133eb0ac, 0x6d8b90a1, 0x450d4467, 0x3bb8646a
};

struct index_entry {
const unsigned char *ptr;
Expand All @@ -42,13 +130,13 @@ struct index_entry {
struct delta_index {
const void *src_buf;
unsigned long src_size;
unsigned int hash_shift;
unsigned int hash_mask;
struct index_entry *hash[0];
};

struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
{
unsigned int i, hsize, hshift, entries, *hash_count;
unsigned int i, hsize, hmask, entries, *hash_count;
const unsigned char *data, *buffer = buf;
struct delta_index *index;
struct index_entry *entry, **hash;
Expand All @@ -57,12 +145,14 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
if (!buf || !bufsize)
return NULL;

/* determine index hash size */
entries = bufsize / BLK_SIZE;
/* Determine index hash size. Note that indexing skips the
first byte to allow for optimizing the rabin polynomial
initialization in create_delta(). */
entries = (bufsize - 1) / RABIN_WINDOW;
hsize = entries / 4;
for (i = 4; (1 << i) < hsize && i < 31; i++);
hsize = 1 << i;
hshift = 32 - i;
hmask = hsize - 1;

/* allocate lookup index */
mem = malloc(sizeof(*index) +
Expand All @@ -78,7 +168,7 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)

index->src_buf = buf;
index->src_size = bufsize;
index->hash_shift = hshift;
index->hash_mask = hmask;
memset(hash, 0, hsize * sizeof(*hash));

/* allocate an array to count hash entries */
Expand All @@ -89,17 +179,19 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
}

/* then populate the index */
data = buffer + entries * BLK_SIZE - BLK_SIZE;
data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
while (data >= buffer) {
unsigned int val = adler32(0, data, BLK_SIZE);
i = HASH(val, hshift);
entry->ptr = data;
unsigned int val = 0;
for (i = 1; i <= RABIN_WINDOW; i++)
val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
i = val & hmask;
entry->ptr = data + RABIN_WINDOW;
entry->val = val;
entry->next = hash[i];
hash[i] = entry++;
hash_count[i]++;
data -= BLK_SIZE;
}
data -= RABIN_WINDOW;
}

/*
* Determine a limit on the number of entries in the same hash
Expand Down Expand Up @@ -136,20 +228,18 @@ void free_delta_index(struct delta_index *index)
free(index);
}

/* provide the size of the copy opcode given the block offset and size */
#define COPYOP_SIZE(o, s) \
(!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
!!(s & 0xff) + !!(s & 0xff00) + 1)

/* the maximum size for any opcode */
#define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
/*
* The maximum size for any opcode sequence, including the initial header
* plus rabin window plus biggest copy.
*/
#define MAX_OP_SIZE (5 + 5 + 1 + RABIN_WINDOW + 7)

void *
create_delta(const struct delta_index *index,
const void *trg_buf, unsigned long trg_size,
unsigned long *delta_size, unsigned long max_size)
{
unsigned int i, outpos, outsize, hash_shift;
unsigned int i, outpos, outsize, hash_mask, val;
int inscnt;
const unsigned char *ref_data, *ref_top, *data, *top;
unsigned char *out;
Expand Down Expand Up @@ -185,14 +275,22 @@ create_delta(const struct delta_index *index,
ref_top = ref_data + index->src_size;
data = trg_buf;
top = trg_buf + trg_size;
hash_shift = index->hash_shift;
inscnt = 0;
hash_mask = index->hash_mask;

outpos++;
val = 0;
for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
out[outpos++] = *data;
val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
}
inscnt = i;

while (data < top) {
unsigned int moff = 0, msize = 0;
struct index_entry *entry;
unsigned int val = adler32(0, data, BLK_SIZE);
i = HASH(val, hash_shift);
val ^= U[data[-RABIN_WINDOW]];
val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
i = val & hash_mask;
for (entry = index->hash[i]; entry; entry = entry->next) {
const unsigned char *ref = entry->ptr;
const unsigned char *src = data;
Expand All @@ -214,7 +312,7 @@ create_delta(const struct delta_index *index,
}
}

if (!msize || msize < COPYOP_SIZE(moff, msize)) {
if (msize < 4) {
if (!inscnt)
outpos++;
out[outpos++] = *data++;
Expand All @@ -226,6 +324,20 @@ create_delta(const struct delta_index *index,
} else {
unsigned char *op;

if (msize >= RABIN_WINDOW) {
const unsigned char *sk;
sk = data + msize - RABIN_WINDOW;
val = 0;
for (i = 0; i < RABIN_WINDOW; i++)
val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
} else {
const unsigned char *sk = data + 1;
for (i = 1; i < msize; i++) {
val ^= U[sk[-RABIN_WINDOW]];
val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
}
}

if (inscnt) {
while (moff && ref_data[moff-1] == data[-1]) {
if (msize == 0x10000)
Expand Down Expand Up @@ -270,9 +382,8 @@ create_delta(const struct delta_index *index,
if (max_size && outsize >= max_size)
outsize = max_size + MAX_OP_SIZE + 1;
if (max_size && outpos > max_size)
out = NULL;
else
out = realloc(out, outsize);
break;
out = realloc(out, outsize);
if (!out) {
free(tmp);
return NULL;
Expand All @@ -283,6 +394,11 @@ create_delta(const struct delta_index *index,
if (inscnt)
out[outpos - inscnt - 1] = inscnt;

if (max_size && outpos > max_size) {
free(out);
return NULL;
}

*delta_size = outpos;
return out;
}

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