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Improved search for the longest run of unallocated blocks

N2009_11_14_FIXES
jpandre 2008-01-15 17:35:05 +00:00
parent 038156ba82
commit d5fc330628
1 changed files with 63 additions and 25 deletions
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88
libntfs-3g/lcnalloc.c
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@ -4,6 +4,7 @@
* Copyright (c) 2002-2004 Anton Altaparmakov
* Copyright (c) 2004 Yura Pakhuchiy
* Copyright (c) 2004-2007 Szabolcs Szakacsits
* Copyright (c) 2008 Jean-Pierre Andre
*
* This program/include file is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as published
@ -81,37 +82,74 @@ static void ntfs_cluster_update_zone_pos(ntfs_volume *vol, u8 zone, LCN tc)
static s64 max_empty_bit_range(unsigned char *buf, int size)
{
int i, j, run = 0;
int max_range = 0;
int max_range;
int i,j;
int run;
unsigned char uncounted;
s64 start_pos = -1;
ntfs_log_trace("Entering\n");
for (i = 0; i < size; i++, buf++) {
if (*buf == 0) {
run += 8;
continue;
}
for (j = 0; j < 8; j++) {
int bit = *buf & (1 << j);
if (bit) {
max_range = 0;
i = 0;
/*
* count every bit until we reach a range of 8
* (fast count if all bits set)
*/
run = 0;
while ((i < size) && (max_range < 8)) {
if (*buf == 255) {
if (run > max_range) {
max_range = run;
start_pos = i * 8 - run;
}
run = 0;
} else
for (j=0; j<8; j++)
if (*buf & (1 << j)) {
if (run > max_range) {
max_range = run;
start_pos = i * 8 + j - run;
}
run = 0;
} else
run++;
i++;
buf++;
}
/*
* From now on, beginning and end are in different bytes
* and we do not count bits unless we have enough
* null bytes
*/
uncounted = 255;
while (i < size) {
if (*buf) {
if ((run + 14) > max_range) {
/* uncounted bits in first byte */
for (j=7; (j>=0) && !(uncounted & (1 << j)); j--)
run++;
/* uncounted bits in last byte */
for (j=0; (j<8) && !(*buf & (1 << j)); j++)
run++;
if (run > max_range) {
max_range = run;
start_pos = i * 8 + j - run;
}
run = 0;
} else
run++;
}
}
uncounted = *buf;
run = 0;
} else
run += 8;
buf++;
i++;
}
if (run > max_range)
start_pos = i * 8 - run;
if ((run + 7) > max_range) {
/* uncounted bits in first byte */
for (j=7; (j>=0) && !(uncounted & (1 << j)); j--)
run++;
if (run > max_range)
start_pos = i * 8 - run;
}
return start_pos;
}