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xdelta.c
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/* -*- Mode: C;-*-
*
* This file is part of XDelta - A binary delta generator.
*
* Copyright (C) 1997, 1998, 1999, 2001 Josh MacDonald
*
* 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* Author: Josh MacDonald <[email protected]>
*
* $Id: xdelta.c 1.4.1.50.1.3 Sun, 24 Feb 2002 11:30:34 -0800 jmacd $
*/
#define G_DISABLE_ASSERT
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include "xdelta.h"
#include "xdeltapriv.h"
/* $Format: "const guint xdelta_major_version = $ReleaseMajorVersion$;" $ */
const guint xdelta_major_version = 1;
/* $Format: "const guint xdelta_minor_version = $ReleaseMinorVersion$;" $ */
const guint xdelta_minor_version = 1;
/* $Format: "const guint xdelta_micro_version = $ReleaseMicroVersion$;" $ */
const guint xdelta_micro_version = 4;
/* Control functions.
*/
static XdeltaControl* control_version_0 (SerialVersion0Control* cont) ;
static void control_copy (XdeltaControl* cont, XdeltaSource* src, guint from, guint to);
static gboolean control_add_info (XdeltaControl* cont, XdeltaSource* src, const guint8* md5, guint len);
#ifndef XDELTA_HARDCODE_SIZE
int QUERY_SIZE = 0;
int QUERY_SIZE_POW = 0;
int QUERY_SIZE_MASK = 0;
#endif
int xdp_set_query_size_pow (int size_pow)
{
#ifdef XDELTA_HARDCODE_SIZE
return XDP_QUERY_HARDCODED;
#else
int x = 1;
int size_log = 0;
for (; x != 0; x <<= 1, size_log += 1)
{
if (x == size_pow)
goto good;
}
return XDP_QUERY_POW2;
good:
QUERY_SIZE = size_log;
QUERY_SIZE_POW = size_pow;
QUERY_SIZE_MASK = size_pow-1;
return 0;
#endif
}
int
xdp_blocksize ()
{
if (QUERY_SIZE == 0)
{
xdp_set_query_size_pow (1<<QUERY_SIZE_DEFAULT);
}
return QUERY_SIZE_POW;
}
const char*
xdp_errno (int errval)
{
switch (errval)
{
case XDP_QUERY_HARDCODED:
return "query size hardcoded";
case XDP_QUERY_POW2:
return "query size must be a power of 2";
}
return g_strerror (errval);
}
const guint16 single_hash[256] =
{
/* Random numbers generated using SLIB's pseudo-random number
* generator. */
0xbcd1, 0xbb65, 0x42c2, 0xdffe, 0x9666, 0x431b, 0x8504, 0xeb46,
0x6379, 0xd460, 0xcf14, 0x53cf, 0xdb51, 0xdb08, 0x12c8, 0xf602,
0xe766, 0x2394, 0x250d, 0xdcbb, 0xa678, 0x02af, 0xa5c6, 0x7ea6,
0xb645, 0xcb4d, 0xc44b, 0xe5dc, 0x9fe6, 0x5b5c, 0x35f5, 0x701a,
0x220f, 0x6c38, 0x1a56, 0x4ca3, 0xffc6, 0xb152, 0x8d61, 0x7a58,
0x9025, 0x8b3d, 0xbf0f, 0x95a3, 0xe5f4, 0xc127, 0x3bed, 0x320b,
0xb7f3, 0x6054, 0x333c, 0xd383, 0x8154, 0x5242, 0x4e0d, 0x0a94,
0x7028, 0x8689, 0x3a22, 0x0980, 0x1847, 0xb0f1, 0x9b5c, 0x4176,
0xb858, 0xd542, 0x1f6c, 0x2497, 0x6a5a, 0x9fa9, 0x8c5a, 0x7743,
0xa8a9, 0x9a02, 0x4918, 0x438c, 0xc388, 0x9e2b, 0x4cad, 0x01b6,
0xab19, 0xf777, 0x365f, 0x1eb2, 0x091e, 0x7bf8, 0x7a8e, 0x5227,
0xeab1, 0x2074, 0x4523, 0xe781, 0x01a3, 0x163d, 0x3b2e, 0x287d,
0x5e7f, 0xa063, 0xb134, 0x8fae, 0x5e8e, 0xb7b7, 0x4548, 0x1f5a,
0xfa56, 0x7a24, 0x900f, 0x42dc, 0xcc69, 0x02a0, 0x0b22, 0xdb31,
0x71fe, 0x0c7d, 0x1732, 0x1159, 0xcb09, 0xe1d2, 0x1351, 0x52e9,
0xf536, 0x5a4f, 0xc316, 0x6bf9, 0x8994, 0xb774, 0x5f3e, 0xf6d6,
0x3a61, 0xf82c, 0xcc22, 0x9d06, 0x299c, 0x09e5, 0x1eec, 0x514f,
0x8d53, 0xa650, 0x5c6e, 0xc577, 0x7958, 0x71ac, 0x8916, 0x9b4f,
0x2c09, 0x5211, 0xf6d8, 0xcaaa, 0xf7ef, 0x287f, 0x7a94, 0xab49,
0xfa2c, 0x7222, 0xe457, 0xd71a, 0x00c3, 0x1a76, 0xe98c, 0xc037,
0x8208, 0x5c2d, 0xdfda, 0xe5f5, 0x0b45, 0x15ce, 0x8a7e, 0xfcad,
0xaa2d, 0x4b5c, 0xd42e, 0xb251, 0x907e, 0x9a47, 0xc9a6, 0xd93f,
0x085e, 0x35ce, 0xa153, 0x7e7b, 0x9f0b, 0x25aa, 0x5d9f, 0xc04d,
0x8a0e, 0x2875, 0x4a1c, 0x295f, 0x1393, 0xf760, 0x9178, 0x0f5b,
0xfa7d, 0x83b4, 0x2082, 0x721d, 0x6462, 0x0368, 0x67e2, 0x8624,
0x194d, 0x22f6, 0x78fb, 0x6791, 0xb238, 0xb332, 0x7276, 0xf272,
0x47ec, 0x4504, 0xa961, 0x9fc8, 0x3fdc, 0xb413, 0x007a, 0x0806,
0x7458, 0x95c6, 0xccaa, 0x18d6, 0xe2ae, 0x1b06, 0xf3f6, 0x5050,
0xc8e8, 0xf4ac, 0xc04c, 0xf41c, 0x992f, 0xae44, 0x5f1b, 0x1113,
0x1738, 0xd9a8, 0x19ea, 0x2d33, 0x9698, 0x2fe9, 0x323f, 0xcde2,
0x6d71, 0xe37d, 0xb697, 0x2c4f, 0x4373, 0x9102, 0x075d, 0x8e25,
0x1672, 0xec28, 0x6acb, 0x86cc, 0x186e, 0x9414, 0xd674, 0xd1a5
};
/* Compute the hash of length len for buf, a single byte array of
* values, by first indexing the random array.
*/
static void
init_query_checksum (const guint8 *buf, XdeltaChecksum *cksum)
{
gint i = QUERY_SIZE_POW;
guint16 low = 0;
guint16 high = 0;
for (; i != 0; i -= 1)
{
low += CHEW(*buf++);
high += low;
}
cksum->low = low;
cksum->high = high;
}
/* Generate checksums
*/
static gboolean
generate_checksums (XdeltaStream *stream,
XdeltaSource *source)
{
gint total_checksums = handle_length (stream) / QUERY_SIZE_POW;
gint checksum_index = 0;
XdeltaChecksum cksum;
XdeltaChecksum *result;
const guint8* segment = NULL, *segment_pointer;
gint segment_len, orig_segment_len;
guint segment_page = 0;
guint pages;
#ifdef DEBUG_CKSUM
g_print ("Total base checksums: %d\n", total_checksums);
#endif
source->ck_count = total_checksums;
if (total_checksums == 0)
return TRUE;
/* This is the in-core FROM checksum table. */
result = g_new (XdeltaChecksum, total_checksums);
source->cksums = result;
for (pages = handle_pages (stream); segment_page <= pages; segment_page += 1)
{
segment_len = handle_map_page (stream, segment_page, &segment);
if (segment_len < 0)
return FALSE;
orig_segment_len = segment_len;
segment_len >>= QUERY_SIZE;
for (segment_pointer = segment;
segment_len != 0;
segment_len -= 1, segment_pointer += QUERY_SIZE_POW)
{
/* note: cheating at the boundaries */
init_query_checksum (segment_pointer, &cksum);
#ifdef DEBUG_CKSUM
g_print ("New cksum %04x %04x indices %d-%d\n",
cksum.low, cksum.high,
checksum_index * QUERY_SIZE_POW, (checksum_index * QUERY_SIZE_POW) + QUERY_SIZE_POW - 1);
#endif
result[checksum_index++] = cksum;
}
if (! handle_unmap_page (stream, segment_page, &segment))
return FALSE;
}
return TRUE;
}
/* $Format: "#define XDELTA_REQUIRED_VERSION \"$ReleaseMajorVersion$.$ReleaseMinorVersion$.\"" $ */
#define XDELTA_REQUIRED_VERSION "1.1."
XdeltaGenerator*
__xdp_generator_new (const char* version)
{
XdeltaGenerator* xg;
if (strncmp (version, XDELTA_REQUIRED_VERSION, strlen (XDELTA_REQUIRED_VERSION)) != 0)
g_error ("XDelta library version mismatched, compiled for %s, running %s\n", version, XDELTA_VERSION);
xg = g_new0 (XdeltaGenerator, 1);
xg->sources = g_ptr_array_new ();
xg->data_source = g_new0 (XdeltaSource, 1);
xg->data_source->name = "(patch data)";
g_ptr_array_add (xg->sources, xg->data_source);
return xg;
}
void
xdp_generator_free (XdeltaGenerator *gen)
{
int i;
for (i = 0; i < gen->sources->len; i += 1)
xdp_source_free (gen->sources->pdata[i]);
g_ptr_array_free (gen->sources, TRUE);
g_free ((void*) gen->table);
g_free (gen);
}
void
init_pos (XdeltaStream* str, XdeltaPos* pos)
{
g_assert (str);
memset (pos, 0, sizeof (*pos));
pos->page_size = handle_pagesize (str);
}
gboolean
check_stream_integrity (XdeltaStream* str, const guint8* md5, guint len)
{
const guint8* act_md5;
if (len != handle_length (str))
{
xd_generate_handleintint_event (EC_XdStreamLengthFailed, str, len, handle_length (str));
return FALSE;
}
act_md5 = handle_checksum_md5 (str);
if (! act_md5)
return FALSE;
if (memcmp (md5, act_md5, 16) != 0)
{
char exp[33], rec[33];
edsio_md5_to_string (md5, exp);
edsio_md5_to_string (act_md5, rec);
xd_generate_handlestringstring_event (EC_XdStreamChecksumFailed, str, exp, rec);
g_free ((void*) act_md5);
return FALSE;
}
g_free ((void*) act_md5);
return TRUE;
}
static gboolean
xdp_source_index_read (XdeltaSource *xs,
XdeltaStream *index_in)
{
SerialSource *ss = handle_source (index_in);
XdeltaIndex *index;
if (! ss)
return FALSE;
/* TODO: free ss */
if (! unserialize_xdeltaindex (ss, &index))
return FALSE;
if (! check_stream_integrity (xs->source_in, index->file_md5, index->file_len))
return FALSE;
xs->ck_count = index->index_len;
xs->cksums = index->index;
return TRUE;
}
static gboolean
xdp_source_index_internal (XdeltaSource *init,
XdeltaStream *source_in,
XdeltaOutStream *index_out)
{
if (! generate_checksums (source_in, init))
return FALSE;
if (index_out)
{
const guint8* source_in_md5;
SerialSink* sink = handle_sink (index_out, NULL, NULL, NULL, NULL);
if (! sink)
return FALSE;
if (! (source_in_md5 = handle_checksum_md5 (source_in)))
return FALSE;
if (! serialize_xdeltaindex (sink,
handle_length (source_in),
source_in_md5,
init->ck_count,
init->cksums))
{
g_free ((void*) source_in_md5);
return FALSE;
}
g_free ((void*) source_in_md5);
if (! handle_close (index_out, 0))
return FALSE;
}
return TRUE;
}
gboolean
xdp_source_index (XdeltaStream *source_in,
XdeltaOutStream *index_out)
{
XdeltaSource* xs = xdp_source_new ("(ignored)", source_in, NULL, index_out);
if (xs)
{
xdp_source_free (xs);
return TRUE;
}
return FALSE;
}
XdeltaSource*
xdp_source_new (const char *name,
XdeltaStream *source_in,
XdeltaStream *index_in,
XdeltaOutStream *index_out)
{
XdeltaSource* xs = g_new0 (XdeltaSource, 1);
xs->source_in = source_in;
xs->name = name;
g_return_val_if_fail (source_in, NULL);
g_return_val_if_fail (index_in ? ! index_out : TRUE, NULL);
xs->index_in = index_in;
xs->index_out = index_out;
xs->source_pos.page_size = handle_pagesize (source_in);
return xs;
}
static gboolean
xdp_source_check_index (XdeltaSource *xs)
{
if (xs->source_index == 0)
return TRUE;
if (! xs->index_in)
return xdp_source_index_internal (xs, xs->source_in, xs->index_out);
else
return xdp_source_index_read (xs, xs->index_in);
}
void
xdp_source_free (XdeltaSource* xs)
{
if (xs)
{
/* if (xs->ckarray) @@@ this is troublesome now
g_free (xs->ckarray);*/
g_free (xs);
}
}
void
xdp_source_add (XdeltaGenerator *gen,
XdeltaSource *src)
{
if (gen->table)
{
g_free ((gpointer)gen->table);
gen->table = NULL;
}
g_ptr_array_add (gen->sources, src);
}
guint
c_hash (const XdeltaChecksum* c)
{
const guint high = c->high;
const guint low = c->low;
const guint it = (high >> 2) + (low << 3) + (high << 16);
return (it ^ high ^ low);
}
static gboolean
region_insert (XdeltaGenerator* gen, const XdeltaPos *xpos, guint len)
{
/* This is a little bit cryptic: the xpos.mem + EXPR expression
* computes the offset into the current page, which is guaranteed
* to be correct since map_page has not occured yet. */
const guint8* buf = xpos->mem + (gen->to_output_pos % xpos->page_size);
if (len == 0)
return TRUE;
#ifdef DEBUG_INST
g_print ("insert %d at %d\n", len, gen->to_output_pos);
#endif
if (! handle_write (gen->data_out, buf, len))
return FALSE;
control_copy (gen->control, gen->data_source, gen->data_output_pos, gen->data_output_pos + len);
gen->to_output_pos += len;
gen->data_output_pos += len;
return TRUE;
}
static gboolean
region_copy (XdeltaGenerator* gen, XdeltaSource* src, guint from, guint to)
{
#ifdef DEBUG_INST
g_print ("copy %d - %d (%d) to %d\n", from, to, to-from, gen->to_output_pos);
#endif
control_copy (gen->control, src, from, to);
gen->to_output_pos += (to-from);
return TRUE;
}
gboolean
unmap_page (XdeltaStream* stream, XdeltaPos* pos)
{
if (! pos->mem)
return TRUE;
if (handle_unmap_page (stream,
pos->mem_page,
&pos->mem))
{
pos->mem = NULL;
return TRUE;
}
return FALSE;
}
gboolean
map_page (XdeltaStream* stream, XdeltaPos* pos)
{
gint on_page;
if (pos->mem && pos->mem_page == pos->page)
return TRUE;
if (pos->mem)
{
if (! handle_unmap_page (stream,
pos->mem_page,
&pos->mem))
return FALSE;
pos->mem = NULL;
}
pos->mem_page = pos->page;
on_page = handle_map_page (stream,
pos->mem_page,
&pos->mem);
if (on_page >= 0)
{
pos->mem_rem = on_page;
return TRUE;
}
return FALSE;
}
static gboolean
try_match (XdeltaGenerator *gen,
XdeltaStream *in,
XdeltaPos *xpos_ptr,
XdeltaSource *src,
guint src_offset,
gboolean *found)
{
XdeltaPos xpos = *xpos_ptr;
XdeltaPos ypos = src->source_pos;
gint rem, remsave;
gint match_forward = 0;
gint match_backward = 0;
gint match_forward_max;
gint match_backward_max;
guint to_offset = XPOS (xpos);
gboolean one_insert = FALSE;
*found = FALSE;
ypos.page = src_offset / ypos.page_size;
ypos.off = src_offset % ypos.page_size;
match_forward_max = MIN (handle_length (in) - to_offset,
handle_length (src->source_in) - src_offset);
match_backward_max = MIN (src_offset, to_offset - gen->to_output_pos);
/* Don't allow backward paging */
match_backward_max = MIN (match_backward_max, xpos.off);
/* We're testing against the negative below. */
match_backward_max = - match_backward_max;
for (; match_backward > match_backward_max; )
{
g_assert (xpos.off != 0);
if (ypos.off == 0)
{
ypos.off = ypos.page_size;
ypos.page -= 1;
}
if (! map_page (src->source_in, &ypos))
goto bail;
rem = MIN (xpos.off, ypos.off);
rem = MIN (match_backward - match_backward_max, rem);
for (; rem > 0; rem -= 1, match_backward -= 1)
{
if (xpos.mem[xpos.off-1] != ypos.mem[ypos.off-1])
goto doneback;
xpos.off -= 1;
ypos.off -= 1;
}
}
doneback:
xpos.page = to_offset / xpos.page_size;
xpos.off = to_offset % xpos.page_size;
ypos.page = src_offset / ypos.page_size;
ypos.off = src_offset % ypos.page_size;
for (; match_forward < match_forward_max; )
{
if (! map_page (src->source_in, &ypos))
goto bail;
/* Fortunately, if this map happens it means that the match must
* be long enough to succeed below, therefore it is safe to write
* the insert out now. */
if (! one_insert && xpos.page != xpos.mem_page)
{
one_insert = TRUE;
if (! region_insert (gen, &xpos, (to_offset + match_backward) - gen->to_output_pos))
goto bail;
}
if (! map_page (in, &xpos))
goto bail;
rem = MIN (xpos.mem_rem - xpos.off, ypos.mem_rem - ypos.off);
rem = MIN (match_forward_max - match_forward, rem);
/* Do a int-wise comparison if the regions are aligned. */
if (rem > (4*sizeof(int)) && (xpos.off % sizeof (int)) == (ypos.off % sizeof(int)))
{
gint is;
const int *xi, *yi;
for (; xpos.off % sizeof(int); rem -= 1, match_forward += 1)
{
if (xpos.mem[xpos.off] != ypos.mem[ypos.off])
goto done;
xpos.off += 1;
ypos.off += 1;
}
remsave = rem;
rem /= sizeof(int);
xi = (const int*) (xpos.mem + xpos.off);
yi = (const int*) (ypos.mem + ypos.off);
is = rem;
for (; rem > 0 && *xi == *yi; )
{
rem -= 1;
xi += 1;
yi += 1;
}
is -= rem;
match_forward += is * sizeof(int);
xpos.off += is * sizeof(int);
ypos.off += is * sizeof(int);
rem = (rem * sizeof(int)) + (remsave % sizeof(int));
}
for (; rem > 0; rem -= 1, match_forward += 1)
{
if (xpos.mem[xpos.off] != ypos.mem[ypos.off])
goto done;
xpos.off += 1;
ypos.off += 1;
}
FLIP_FORWARD (xpos);
FLIP_FORWARD (ypos);
}
done:
if (match_forward - match_backward >= QUERY_SIZE_POW)
{
*found = TRUE;
if (! one_insert)
{
if (! region_insert (gen, &xpos, (to_offset + match_backward) - gen->to_output_pos))
goto bail;
}
if (! region_copy (gen, src, src_offset + match_backward, src_offset + match_forward))
goto bail;
}
else
{
g_assert (! one_insert);
}
*xpos_ptr = xpos;
src->source_pos = ypos;
return TRUE;
bail:
*xpos_ptr = xpos;
src->source_pos = ypos;
return FALSE;
}
static gboolean
compute_copies (XdeltaGenerator* gen, XdeltaStream* stream)
{
XdeltaChecksum cksum;
const XdeltaChecksum *source_cksum;
const guint8 *segment_pointer;
guint source_offset, segment_index, index, prime = gen->table_size;
guint source_index;
const guint32* table = gen->table;
guint16 old_c, new_c;
guint save_page, save_off;
#ifdef DEBUG_MATCH_PRINT
guint i;
#endif
XdeltaPos xpos;
gboolean found;
gboolean ret = TRUE;
if (handle_length (stream) < QUERY_SIZE_POW)
return TRUE;
init_pos (stream, &xpos);
while (XPOS (xpos) <= (handle_length (stream) - QUERY_SIZE_POW))
{
if (!map_page (stream, &xpos))
return FALSE;
g_assert (xpos.mem_rem > xpos.off);
segment_index = (xpos.mem_rem - xpos.off);
if (segment_index < QUERY_SIZE_POW)
goto nextpage;
segment_index -= QUERY_SIZE_POW;
segment_pointer = xpos.mem + xpos.off;
init_query_checksum (segment_pointer, &cksum);
for (; ; segment_pointer += 1)
{
#ifdef DEBUG_CKSUM_UPDATE
XdeltaChecksum cktest;
init_query_checksum (segment_pointer, &cktest);
if (cktest.high != cksum.high || cktest.low != cktest.low)
abort ();
#endif
index = c_hash (&cksum) % prime;
#ifdef DEBUG_MATCH_PRINT
g_print ("%d: searching for match \"", XPOS(xpos));
for (i = 0; i < QUERY_SIZE_POW; i += 1)
{
if (isprint (segment_pointer[i]))
g_print ("%c", segment_pointer[i]);
else
g_print ("\\0%o", segment_pointer[i]);
}
g_print ("\"... %s\n", table[index] ? "found" : "notfound");
#endif
if (table[index])
{
source_index = (table[index] & QUERY_SIZE_MASK) - 1;
source_offset = (table[index] >> QUERY_SIZE);
source_cksum = ((XdeltaSource*)gen->sources->pdata[source_index])->cksums + source_offset;
if (cksum.high == source_cksum->high &&
cksum.low == source_cksum->low)
{
save_page = xpos.page;
save_off = xpos.off;
if (! try_match (gen,
stream,
&xpos,
gen->sources->pdata[source_index],
source_offset << QUERY_SIZE,
&found))
{
ret = FALSE;
goto bail;
}
if (found)
{
g_assert (xpos.page*xpos.page_size+xpos.off == gen->to_output_pos);
goto reenter;
}
else
{
xpos.page = save_page;
xpos.off = save_off;
}
}
}
if (segment_index == 0)
goto nextpage;
segment_index -= 1;
xpos.off += 1;
old_c = CHEW(segment_pointer[0]);
new_c = CHEW(segment_pointer[QUERY_SIZE_POW]);
cksum.low -= old_c;
cksum.low += new_c;
cksum.high -= old_c << QUERY_SIZE;
cksum.high += cksum.low;
}
nextpage:
if (xpos.mem_rem < xpos.page_size)
break;
xpos.page += 1;
xpos.off = 0;
if (xpos.page != xpos.mem_page)
{
if (! region_insert (gen, &xpos, XPOS (xpos) - gen->to_output_pos))
return FALSE;
}
reenter:
(void) 0;
}
xpos.off = gen->to_output_pos % handle_pagesize (stream);
while (gen->to_output_pos < handle_length (stream))
{
if (! map_page (stream, &xpos))
return FALSE;
if (! region_insert (gen, &xpos, xpos.mem_rem - xpos.off))
ret = FALSE;
xpos.off = 0;
xpos.page += 1;
}
bail:
if (! unmap_page (stream, &xpos))
return FALSE;
return ret;
}
static gboolean
just_output (XdeltaGenerator *gen,
XdeltaStream *in)
{
XdeltaPos pos;
init_pos (in, &pos);
while (gen->to_output_pos < handle_length (in))
{
if (! map_page (in, &pos))
return FALSE;
if (! region_insert (gen, &pos, pos.mem_rem - pos.off))
return FALSE;
pos.off = 0;
pos.page += 1;
}
if (! unmap_page (in, &pos))
return FALSE;
return TRUE;
}
/* Clobbering decision (see below):
*
* Algorithm A: Clobber it always (its fast!). The problem
* is that this prefers matches at the front of
* the file and leads to poor matches at the back
* of the file (assuming I insert going backwards).
*
* Algorithm B: Keep a table of how many times there has
* been a clobber at each index i, C[i].
* With probability 1/(C[i]+1), replace the
* previous entry. This gives a uniform
* probability of each entry surviving.
* The problem (supposed) with this
* algorithm is that the probabilities
* should not be uniform (though uniform is
* better than A) because there are more
* chances to match a segment at the end of
* the file than at the beginning.
*
* Algorithm C: Give a linear weight to each match
* according to it's position in the file
* -- number the segments from N down to 1
* starting at the beginning. Same as the
* above but with a different weight. The
* weight for segment i, match at checksum
* offset k, follows. The total number of
* checksums in the segment is C_i,
* therefore the total checksum count is
* C = sum_i (C_i).
* Now the interior weight is the (C_i-k)
* (the linear assumption) and the total
* interior weight is sum_{j=1}^{N}{j}=(N)(N+1)/2
* so the kth segment has interior weight
*
* [2 (C_i - k)] / [(C_i) (C_i + 1)]
*
* add in the exterior weight (after
* cancelling a C_i):
*
* w(i,k) = [2 (C_i - k)] / [(C_i + 1) (C)]
*
* Now, as above, we will compute whether to
* keep or replace the current value at the j-th
* decision. Let R_j be the running sum of
* weights considered so far. R_0 = 0. At the
* j-th decision,
*
* P_ikj(use new value) = w(i,k)/R_{j+1}
* R_{j+1} = R_j + w(i,k)
*/
static gboolean
xdp_generate_delta_int (XdeltaGenerator *gen,
XdeltaStream *in,
XdeltaOutStream *control_out,
XdeltaOutStream *data_out)
{
gint i, j, total_from_ck_count = 0, prime = 0, index = 0;
gint total_from_len = 0;
guint32* table = NULL;
if (QUERY_SIZE == 0)
{
xdp_set_query_size_pow (1<<QUERY_SIZE_DEFAULT);
}
if (gen->sources->len == 0)
{
xd_generate_void_event (EC_XdTooFewSources);
return FALSE;
}
for (i = 0; i < gen->sources->len; i += 1)
{
XdeltaSource* src = gen->sources->pdata[i];
src->used = FALSE;
src->sequential = TRUE;
src->position = 0;
src->source_index = i;
if (src->source_index != 0)
total_from_len += handle_length (src->source_in);
}
/* QUERY_SIZE_POW is the number of elements freed in the cksum hash
* table for storing segment number + (offset/QUERY_SIZE_POW) in. 1
* for the zero + 1 for the data segment */
if (gen->sources->len > (QUERY_SIZE_POW-2))
{
xd_generate_void_event (EC_XdTooManySources);
return FALSE;
}
if (handle_length (in) < QUERY_SIZE_POW || total_from_len < QUERY_SIZE_POW)
{
if (! just_output (gen, in))
return FALSE;
}
else