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-rw-r--r--bzip2.1.preformatted247
1 files changed, 124 insertions, 123 deletions
diff --git a/bzip2.1.preformatted b/bzip2.1.preformatted
index 0f20cb5..129ca83 100644
--- a/bzip2.1.preformatted
+++ b/bzip2.1.preformatted
@@ -3,43 +3,43 @@ bzip2(1) bzip2(1)
3 3
4 4
5NNAAMMEE 5NNAAMMEE
6 bzip2, bunzip2 - a block-sorting file compressor, v1.0.2 6 bzip2, bunzip2 a blocksorting file compressor, v1.0.3
7 bzcat - decompresses files to stdout 7 bzcat decompresses files to stdout
8 bzip2recover - recovers data from damaged bzip2 files 8 bzip2recover recovers data from damaged bzip2 files
9 9
10 10
11SSYYNNOOPPSSIISS 11SSYYNNOOPPSSIISS
12 bbzziipp22 [ --ccddffkkqqssttvvzzVVLL112233445566778899 ] [ _f_i_l_e_n_a_m_e_s _._._. ] 12 bbzziipp22 [ −−ccddffkkqqssttvvzzVVLL112233445566778899 ] [ _f_i_l_e_n_a_m_e_s _._._. ]
13 bbuunnzziipp22 [ --ffkkvvssVVLL ] [ _f_i_l_e_n_a_m_e_s _._._. ] 13 bbuunnzziipp22 [ ffkkvvssVVLL ] [ _f_i_l_e_n_a_m_e_s _._._. ]
14 bbzzccaatt [ --ss ] [ _f_i_l_e_n_a_m_e_s _._._. ] 14 bbzzccaatt [ ss ] [ _f_i_l_e_n_a_m_e_s _._._. ]
15 bbzziipp22rreeccoovveerr _f_i_l_e_n_a_m_e 15 bbzziipp22rreeccoovveerr _f_i_l_e_n_a_m_e
16 16
17 17
18DDEESSCCRRIIPPTTIIOONN 18DDEESSCCRRIIPPTTIIOONN
19 _b_z_i_p_2 compresses files using the Burrows-Wheeler block 19 _b_z_i_p_2 compresses files using the BurrowsWheeler block
20 sorting text compression algorithm, and Huffman coding. 20 sorting text compression algorithm, and Huffman coding.
21 Compression is generally considerably better than that 21 Compression is generally considerably better than that
22 achieved by more conventional LZ77/LZ78-based compressors, 22 achieved by more conventional LZ77/LZ78based compressors,
23 and approaches the performance of the PPM family of sta 23 and approaches the performance of the PPM family of sta
24 tistical compressors. 24 tistical compressors.
25 25
26 The command-line options are deliberately very similar to 26 The commandline options are deliberately very similar to
27 those of _G_N_U _g_z_i_p_, but they are not identical. 27 those of _G_N_U _g_z_i_p_, but they are not identical.
28 28
29 _b_z_i_p_2 expects a list of file names to accompany the com 29 _b_z_i_p_2 expects a list of file names to accompany the com
30 mand-line flags. Each file is replaced by a compressed 30 mandline flags. Each file is replaced by a compressed
31 version of itself, with the name "original_name.bz2". 31 version of itself, with the name "original_name.bz2".
32 Each compressed file has the same modification date, per 32 Each compressed file has the same modification date, per
33 missions, and, when possible, ownership as the correspond 33 missions, and, when possible, ownership as the correspond
34 ing original, so that these properties can be correctly 34 ing original, so that these properties can be correctly
35 restored at decompression time. File name handling is 35 restored at decompression time. File name handling is
36 naive in the sense that there is no mechanism for preserv 36 naive in the sense that there is no mechanism for preserv
37 ing original file names, permissions, ownerships or dates 37 ing original file names, permissions, ownerships or dates
38 in filesystems which lack these concepts, or have serious 38 in filesystems which lack these concepts, or have serious
39 file name length restrictions, such as MS-DOS. 39 file name length restrictions, such as MSDOS.
40 40
41 _b_z_i_p_2 and _b_u_n_z_i_p_2 will by default not overwrite existing 41 _b_z_i_p_2 and _b_u_n_z_i_p_2 will by default not overwrite existing
42 files. If you want this to happen, specify the -f flag. 42 files. If you want this to happen, specify the f flag.
43 43
44 If no file names are specified, _b_z_i_p_2 compresses from 44 If no file names are specified, _b_z_i_p_2 compresses from
45 standard input to standard output. In this case, _b_z_i_p_2 45 standard input to standard output. In this case, _b_z_i_p_2
@@ -47,7 +47,7 @@ DDEESSCCRRIIPPTTIIOONN
47 this would be entirely incomprehensible and therefore 47 this would be entirely incomprehensible and therefore
48 pointless. 48 pointless.
49 49
50 _b_u_n_z_i_p_2 (or _b_z_i_p_2 _-_d_) decompresses all specified files. 50 _b_u_n_z_i_p_2 (or _b_z_i_p_2 __d_) decompresses all specified files.
51 Files which were not created by _b_z_i_p_2 will be detected and 51 Files which were not created by _b_z_i_p_2 will be detected and
52 ignored, and a warning issued. _b_z_i_p_2 attempts to guess 52 ignored, and a warning issued. _b_z_i_p_2 attempts to guess
53 the filename for the decompressed file from that of the 53 the filename for the decompressed file from that of the
@@ -64,26 +64,26 @@ DDEESSCCRRIIPPTTIIOONN
64 guess the name of the original file, and uses the original 64 guess the name of the original file, and uses the original
65 name with _._o_u_t appended. 65 name with _._o_u_t appended.
66 66
67 As with compression, supplying no filenames causes decom 67 As with compression, supplying no filenames causes decom
68 pression from standard input to standard output. 68 pression from standard input to standard output.
69 69
70 _b_u_n_z_i_p_2 will correctly decompress a file which is the con 70 _b_u_n_z_i_p_2 will correctly decompress a file which is the con
71 catenation of two or more compressed files. The result is 71 catenation of two or more compressed files. The result is
72 the concatenation of the corresponding uncompressed files. 72 the concatenation of the corresponding uncompressed files.
73 Integrity testing (-t) of concatenated compressed files is 73 Integrity testing (t) of concatenated compressed files is
74 also supported. 74 also supported.
75 75
76 You can also compress or decompress files to the standard 76 You can also compress or decompress files to the standard
77 output by giving the -c flag. Multiple files may be com 77 output by giving the c flag. Multiple files may be com
78 pressed and decompressed like this. The resulting outputs 78 pressed and decompressed like this. The resulting outputs
79 are fed sequentially to stdout. Compression of multiple 79 are fed sequentially to stdout. Compression of multiple
80 files in this manner generates a stream containing multi 80 files in this manner generates a stream containing multi
81 ple compressed file representations. Such a stream can be 81 ple compressed file representations. Such a stream can be
82 decompressed correctly only by _b_z_i_p_2 version 0.9.0 or 82 decompressed correctly only by _b_z_i_p_2 version 0.9.0 or
83 later. Earlier versions of _b_z_i_p_2 will stop after decom 83 later. Earlier versions of _b_z_i_p_2 will stop after decom
84 pressing the first file in the stream. 84 pressing the first file in the stream.
85 85
86 _b_z_c_a_t (or _b_z_i_p_2 _-_d_c_) decompresses all specified files to 86 _b_z_c_a_t (or _b_z_i_p_2 __d_c_) decompresses all specified files to
87 the standard output. 87 the standard output.
88 88
89 _b_z_i_p_2 will read arguments from the environment variables 89 _b_z_i_p_2 will read arguments from the environment variables
@@ -99,15 +99,15 @@ DDEESSCCRRIIPPTTIIOONN
99 most file compressors) is coded at about 8.05 bits per 99 most file compressors) is coded at about 8.05 bits per
100 byte, giving an expansion of around 0.5%. 100 byte, giving an expansion of around 0.5%.
101 101
102 As a self-check for your protection, _b_z_i_p_2 uses 32-bit 102 As a selfcheck for your protection, _b_z_i_p_2 uses 32bit
103 CRCs to make sure that the decompressed version of a file 103 CRCs to make sure that the decompressed version of a file
104 is identical to the original. This guards against corrup 104 is identical to the original. This guards against corrup
105 tion of the compressed data, and against undetected bugs 105 tion of the compressed data, and against undetected bugs
106 in _b_z_i_p_2 (hopefully very unlikely). The chances of data 106 in _b_z_i_p_2 (hopefully very unlikely). The chances of data
107 corruption going undetected is microscopic, about one 107 corruption going undetected is microscopic, about one
108 chance in four billion for each file processed. Be aware, 108 chance in four billion for each file processed. Be aware,
109 though, that the check occurs upon decompression, so it 109 though, that the check occurs upon decompression, so it
110 can only tell you that something is wrong. It can't help 110 can only tell you that something is wrong. It cant help
111 you recover the original uncompressed data. You can use 111 you recover the original uncompressed data. You can use
112 _b_z_i_p_2_r_e_c_o_v_e_r to try to recover data from damaged files. 112 _b_z_i_p_2_r_e_c_o_v_e_r to try to recover data from damaged files.
113 113
@@ -118,41 +118,41 @@ DDEESSCCRRIIPPTTIIOONN
118 118
119 119
120OOPPTTIIOONNSS 120OOPPTTIIOONNSS
121 --cc ----ssttddoouutt 121 cc ‐‐ssttddoouutt
122 Compress or decompress to standard output. 122 Compress or decompress to standard output.
123 123
124 --dd ----ddeeccoommpprreessss 124 dd ‐‐ddeeccoommpprreessss
125 Force decompression. _b_z_i_p_2_, _b_u_n_z_i_p_2 and _b_z_c_a_t are 125 Force decompression. _b_z_i_p_2_, _b_u_n_z_i_p_2 and _b_z_c_a_t are
126 really the same program, and the decision about 126 really the same program, and the decision about
127 what actions to take is done on the basis of which 127 what actions to take is done on the basis of which
128 name is used. This flag overrides that mechanism, 128 name is used. This flag overrides that mechanism,
129 and forces _b_z_i_p_2 to decompress. 129 and forces _b_z_i_p_2 to decompress.
130 130
131 --zz ----ccoommpprreessss 131 zz ‐‐ccoommpprreessss
132 The complement to -d: forces compression, 132 The complement to d: forces compression,
133 regardless of the invocation name. 133 regardless of the invocation name.
134 134
135 --tt ----tteesstt 135 tt ‐‐tteesstt
136 Check integrity of the specified file(s), but don't 136 Check integrity of the specified file(s), but dont
137 decompress them. This really performs a trial 137 decompress them. This really performs a trial
138 decompression and throws away the result. 138 decompression and throws away the result.
139 139
140 --ff ----ffoorrccee 140 ff ‐‐ffoorrccee
141 Force overwrite of output files. Normally, _b_z_i_p_2 141 Force overwrite of output files. Normally, _b_z_i_p_2
142 will not overwrite existing output files. Also 142 will not overwrite existing output files. Also
143 forces _b_z_i_p_2 to break hard links to files, which it 143 forces _b_z_i_p_2 to break hard links to files, which it
144 otherwise wouldn't do. 144 otherwise wouldnt do.
145 145
146 bzip2 normally declines to decompress files which 146 bzip2 normally declines to decompress files which
147 don't have the correct magic header bytes. If 147 dont have the correct magic header bytes. If
148 forced (-f), however, it will pass such files 148 forced (f), however, it will pass such files
149 through unmodified. This is how GNU gzip behaves. 149 through unmodified. This is how GNU gzip behaves.
150 150
151 --kk ----kkeeeepp 151 kk ‐‐kkeeeepp
152 Keep (don't delete) input files during compression 152 Keep (dont delete) input files during compression
153 or decompression. 153 or decompression.
154 154
155 --ss ----ssmmaallll 155 ss ‐‐ssmmaallll
156 Reduce memory usage, for compression, decompression 156 Reduce memory usage, for compression, decompression
157 and testing. Files are decompressed and tested 157 and testing. Files are decompressed and tested
158 using a modified algorithm which only requires 2.5 158 using a modified algorithm which only requires 2.5
@@ -160,46 +160,46 @@ OOPPTTIIOONNSS
160 decompressed in 2300k of memory, albeit at about 160 decompressed in 2300k of memory, albeit at about
161 half the normal speed. 161 half the normal speed.
162 162
163 During compression, -s selects a block size of 163 During compression, s selects a block size of
164 200k, which limits memory use to around the same 164 200k, which limits memory use to around the same
165 figure, at the expense of your compression ratio. 165 figure, at the expense of your compression ratio.
166 In short, if your machine is low on memory (8 166 In short, if your machine is low on memory (8
167 megabytes or less), use -s for everything. See 167 megabytes or less), use s for everything. See
168 MEMORY MANAGEMENT below. 168 MEMORY MANAGEMENT below.
169 169
170 --qq ----qquuiieett 170 qq ‐‐qquuiieett
171 Suppress non-essential warning messages. Messages 171 Suppress nonessential warning messages. Messages
172 pertaining to I/O errors and other critical events 172 pertaining to I/O errors and other critical events
173 will not be suppressed. 173 will not be suppressed.
174 174
175 --vv ----vveerrbboossee 175 vv ‐‐vveerrbboossee
176 Verbose mode -- show the compression ratio for each 176 Verbose mode ‐‐ show the compression ratio for each
177 file processed. Further -v's increase the ver 177 file processed. Further vs increase the ver
178 bosity level, spewing out lots of information which 178 bosity level, spewing out lots of information which
179 is primarily of interest for diagnostic purposes. 179 is primarily of interest for diagnostic purposes.
180 180
181 --LL ----lliicceennssee --VV ----vveerrssiioonn 181 LL ‐‐lliicceennssee VV ‐‐vveerrssiioonn
182 Display the software version, license terms and 182 Display the software version, license terms and
183 conditions. 183 conditions.
184 184
185 --11 ((oorr ----ffaasstt)) ttoo --99 ((oorr ----bbeesstt)) 185 11 ((oorr −−ffaasstt)) ttoo 99 ((oorr −−bbeesstt))
186 Set the block size to 100 k, 200 k .. 900 k when 186 Set the block size to 100 k, 200 k .. 900 k when
187 compressing. Has no effect when decompressing. 187 compressing. Has no effect when decompressing.
188 See MEMORY MANAGEMENT below. The --fast and --best 188 See MEMORY MANAGEMENT below. The −−fast and −−best
189 aliases are primarily for GNU gzip compatibility. 189 aliases are primarily for GNU gzip compatibility.
190 In particular, --fast doesn't make things signifi 190 In particular, −−fast doesnt make things signifi
191 cantly faster. And --best merely selects the 191 cantly faster. And −−best merely selects the
192 default behaviour. 192 default behaviour.
193 193
194 ---- Treats all subsequent arguments as file names, even 194 −‐ Treats all subsequent arguments as file names, even
195 if they start with a dash. This is so you can han 195 if they start with a dash. This is so you can han
196 dle files with names beginning with a dash, for 196 dle files with names beginning with a dash, for
197 example: bzip2 -- -myfilename. 197 example: bzip2 −‐ myfilename.
198 198
199 ----rreeppeettiittiivvee--ffaasstt ----rreeppeettiittiivvee--bbeesstt 199 −−‐‐rreeppeettiittiivvee‐‐ffaasstt ‐‐‐‐rreeppeettiittiivvee‐‐bbeesstt
200 These flags are redundant in versions 0.9.5 and 200 These flags are redundant in versions 0.9.5 and
201 above. They provided some coarse control over the 201 above. They provided some coarse control over the
202 behaviour of the sorting algorithm in earlier ver 202 behaviour of the sorting algorithm in earlier ver
203 sions, which was sometimes useful. 0.9.5 and above 203 sions, which was sometimes useful. 0.9.5 and above
204 have an improved algorithm which renders these 204 have an improved algorithm which renders these
205 flags irrelevant. 205 flags irrelevant.
@@ -209,13 +209,13 @@ MMEEMMOORRYY MMAANNAAGGEEMMEENNTT
209 _b_z_i_p_2 compresses large files in blocks. The block size 209 _b_z_i_p_2 compresses large files in blocks. The block size
210 affects both the compression ratio achieved, and the 210 affects both the compression ratio achieved, and the
211 amount of memory needed for compression and decompression. 211 amount of memory needed for compression and decompression.
212 The flags -1 through -9 specify the block size to be 212 The flags 1 through 9 specify the block size to be
213 100,000 bytes through 900,000 bytes (the default) respec 213 100,000 bytes through 900,000 bytes (the default) respec
214 tively. At decompression time, the block size used for 214 tively. At decompression time, the block size used for
215 compression is read from the header of the compressed 215 compression is read from the header of the compressed
216 file, and _b_u_n_z_i_p_2 then allocates itself just enough memory 216 file, and _b_u_n_z_i_p_2 then allocates itself just enough memory
217 to decompress the file. Since block sizes are stored in 217 to decompress the file. Since block sizes are stored in
218 compressed files, it follows that the flags -1 to -9 are 218 compressed files, it follows that the flags 1 to 9 are
219 irrelevant to and so ignored during decompression. 219 irrelevant to and so ignored during decompression.
220 220
221 Compression and decompression requirements, in bytes, can 221 Compression and decompression requirements, in bytes, can
@@ -238,21 +238,21 @@ MMEEMMOORRYY MMAANNAAGGEEMMEENNTT
238 _b_u_n_z_i_p_2 will require about 3700 kbytes to decompress. To 238 _b_u_n_z_i_p_2 will require about 3700 kbytes to decompress. To
239 support decompression of any file on a 4 megabyte machine, 239 support decompression of any file on a 4 megabyte machine,
240 _b_u_n_z_i_p_2 has an option to decompress using approximately 240 _b_u_n_z_i_p_2 has an option to decompress using approximately
241 half this amount of memory, about 2300 kbytes. Decompres 241 half this amount of memory, about 2300 kbytes. Decompres
242 sion speed is also halved, so you should use this option 242 sion speed is also halved, so you should use this option
243 only where necessary. The relevant flag is -s. 243 only where necessary. The relevant flag is s.
244 244
245 In general, try and use the largest block size memory con 245 In general, try and use the largest block size memory con
246 straints allow, since that maximises the compression 246 straints allow, since that maximises the compression
247 achieved. Compression and decompression speed are virtu 247 achieved. Compression and decompression speed are virtu
248 ally unaffected by block size. 248 ally unaffected by block size.
249 249
250 Another significant point applies to files which fit in a 250 Another significant point applies to files which fit in a
251 single block -- that means most files you'd encounter 251 single block ‐‐ that means most files youd encounter
252 using a large block size. The amount of real memory 252 using a large block size. The amount of real memory
253 touched is proportional to the size of the file, since the 253 touched is proportional to the size of the file, since the
254 file is smaller than a block. For example, compressing a 254 file is smaller than a block. For example, compressing a
255 file 20,000 bytes long with the flag -9 will cause the 255 file 20,000 bytes long with the flag 9 will cause the
256 compressor to allocate around 7600k of memory, but only 256 compressor to allocate around 7600k of memory, but only
257 touch 400k + 20000 * 8 = 560 kbytes of it. Similarly, the 257 touch 400k + 20000 * 8 = 560 kbytes of it. Similarly, the
258 decompressor will allocate 3700k but only touch 100k + 258 decompressor will allocate 3700k but only touch 100k +
@@ -260,59 +260,59 @@ MMEEMMOORRYY MMAANNAAGGEEMMEENNTT
260 260
261 Here is a table which summarises the maximum memory usage 261 Here is a table which summarises the maximum memory usage
262 for different block sizes. Also recorded is the total 262 for different block sizes. Also recorded is the total
263 compressed size for 14 files of the Calgary Text Compres 263 compressed size for 14 files of the Calgary Text Compres
264 sion Corpus totalling 3,141,622 bytes. This column gives 264 sion Corpus totalling 3,141,622 bytes. This column gives
265 some feel for how compression varies with block size. 265 some feel for how compression varies with block size.
266 These figures tend to understate the advantage of larger 266 These figures tend to understate the advantage of larger
267 block sizes for larger files, since the Corpus is domi 267 block sizes for larger files, since the Corpus is domi
268 nated by smaller files. 268 nated by smaller files.
269 269
270 Compress Decompress Decompress Corpus 270 Compress Decompress Decompress Corpus
271 Flag usage usage -s usage Size 271 Flag usage usage s usage Size
272 272
273 -1 1200k 500k 350k 914704 273 1 1200k 500k 350k 914704
274 -2 2000k 900k 600k 877703 274 2 2000k 900k 600k 877703
275 -3 2800k 1300k 850k 860338 275 3 2800k 1300k 850k 860338
276 -4 3600k 1700k 1100k 846899 276 4 3600k 1700k 1100k 846899
277 -5 4400k 2100k 1350k 845160 277 5 4400k 2100k 1350k 845160
278 -6 5200k 2500k 1600k 838626 278 6 5200k 2500k 1600k 838626
279 -7 6100k 2900k 1850k 834096 279 7 6100k 2900k 1850k 834096
280 -8 6800k 3300k 2100k 828642 280 8 6800k 3300k 2100k 828642
281 -9 7600k 3700k 2350k 828642 281 9 7600k 3700k 2350k 828642
282 282
283 283
284RREECCOOVVEERRIINNGG DDAATTAA FFRROOMM DDAAMMAAGGEEDD FFIILLEESS 284RREECCOOVVEERRIINNGG DDAATTAA FFRROOMM DDAAMMAAGGEEDD FFIILLEESS
285 _b_z_i_p_2 compresses files in blocks, usually 900kbytes long. 285 _b_z_i_p_2 compresses files in blocks, usually 900kbytes long.
286 Each block is handled independently. If a media or trans 286 Each block is handled independently. If a media or trans
287 mission error causes a multi-block .bz2 file to become 287 mission error causes a multiblock .bz2 file to become
288 damaged, it may be possible to recover data from the 288 damaged, it may be possible to recover data from the
289 undamaged blocks in the file. 289 undamaged blocks in the file.
290 290
291 The compressed representation of each block is delimited 291 The compressed representation of each block is delimited
292 by a 48-bit pattern, which makes it possible to find the 292 by a 48bit pattern, which makes it possible to find the
293 block boundaries with reasonable certainty. Each block 293 block boundaries with reasonable certainty. Each block
294 also carries its own 32-bit CRC, so damaged blocks can be 294 also carries its own 32bit CRC, so damaged blocks can be
295 distinguished from undamaged ones. 295 distinguished from undamaged ones.
296 296
297 _b_z_i_p_2_r_e_c_o_v_e_r is a simple program whose purpose is to 297 _b_z_i_p_2_r_e_c_o_v_e_r is a simple program whose purpose is to
298 search for blocks in .bz2 files, and write each block out 298 search for blocks in .bz2 files, and write each block out
299 into its own .bz2 file. You can then use _b_z_i_p_2 -t to test 299 into its own .bz2 file. You can then use _b_z_i_p_2 t to test
300 the integrity of the resulting files, and decompress those 300 the integrity of the resulting files, and decompress those
301 which are undamaged. 301 which are undamaged.
302 302
303 _b_z_i_p_2_r_e_c_o_v_e_r takes a single argument, the name of the dam 303 _b_z_i_p_2_r_e_c_o_v_e_r takes a single argument, the name of the dam
304 aged file, and writes a number of files 304 aged file, and writes a number of files
305 "rec00001file.bz2", "rec00002file.bz2", etc, containing 305 "rec00001file.bz2", "rec00002file.bz2", etc, containing
306 the extracted blocks. The output filenames are 306 the extracted blocks. The output filenames are
307 designed so that the use of wildcards in subsequent pro 307 designed so that the use of wildcards in subsequent pro
308 cessing -- for example, "bzip2 -dc rec*file.bz2 > recov 308 cessing ‐‐ for example, "bzip2 dc rec*file.bz2 > recov
309 ered_data" -- processes the files in the correct order. 309 ered_data" ‐‐ processes the files in the correct order.
310 310
311 _b_z_i_p_2_r_e_c_o_v_e_r should be of most use dealing with large .bz2 311 _b_z_i_p_2_r_e_c_o_v_e_r should be of most use dealing with large .bz2
312 files, as these will contain many blocks. It is clearly 312 files, as these will contain many blocks. It is clearly
313 futile to use it on damaged single-block files, since a 313 futile to use it on damaged singleblock files, since a
314 damaged block cannot be recovered. If you wish to min 314 damaged block cannot be recovered. If you wish to min
315 imise any potential data loss through media or transmis 315 imise any potential data loss through media or transmis
316 sion errors, you might consider compressing with a smaller 316 sion errors, you might consider compressing with a smaller
317 block size. 317 block size.
318 318
@@ -324,21 +324,21 @@ PPEERRFFOORRMMAANNCCEE NNOOTTEESS
324 ..." (repeated several hundred times) may compress more 324 ..." (repeated several hundred times) may compress more
325 slowly than normal. Versions 0.9.5 and above fare much 325 slowly than normal. Versions 0.9.5 and above fare much
326 better than previous versions in this respect. The ratio 326 better than previous versions in this respect. The ratio
327 between worst-case and average-case compression time is in 327 between worstcase and averagecase compression time is in
328 the region of 10:1. For previous versions, this figure 328 the region of 10:1. For previous versions, this figure
329 was more like 100:1. You can use the -vvvv option to mon 329 was more like 100:1. You can use the vvvv option to mon
330 itor progress in great detail, if you want. 330 itor progress in great detail, if you want.
331 331
332 Decompression speed is unaffected by these phenomena. 332 Decompression speed is unaffected by these phenomena.
333 333
334 _b_z_i_p_2 usually allocates several megabytes of memory to 334 _b_z_i_p_2 usually allocates several megabytes of memory to
335 operate in, and then charges all over it in a fairly ran 335 operate in, and then charges all over it in a fairly ran
336 dom fashion. This means that performance, both for com 336 dom fashion. This means that performance, both for com
337 pressing and decompressing, is largely determined by the 337 pressing and decompressing, is largely determined by the
338 speed at which your machine can service cache misses. 338 speed at which your machine can service cache misses.
339 Because of this, small changes to the code to reduce the 339 Because of this, small changes to the code to reduce the
340 miss rate have been observed to give disproportionately 340 miss rate have been observed to give disproportionately
341 large performance improvements. I imagine _b_z_i_p_2 will per 341 large performance improvements. I imagine _b_z_i_p_2 will per
342 form best on machines with very large caches. 342 form best on machines with very large caches.
343 343
344 344
@@ -348,50 +348,51 @@ CCAAVVEEAATTSS
348 but the details of what the problem is sometimes seem 348 but the details of what the problem is sometimes seem
349 rather misleading. 349 rather misleading.
350 350
351 This manual page pertains to version 1.0.2 of _b_z_i_p_2_. Com 351 This manual page pertains to version 1.0.3 of _b_z_i_p_2_. Com
352 pressed data created by this version is entirely forwards 352 pressed data created by this version is entirely forwards
353 and backwards compatible with the previous public 353 and backwards compatible with the previous public
354 releases, versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0 and 1.0.1, 354 releases, versions 0.1pl2, 0.9.0, 0.9.5, 1.0.0, 1.0.1 and
355 but with the following exception: 0.9.0 and above can cor 355 1.0.2, but with the following exception: 0.9.0 and above
356 rectly decompress multiple concatenated compressed files. 356 can correctly decompress multiple concatenated compressed
357 0.1pl2 cannot do this; it will stop after decompressing 357 files. 0.1pl2 cannot do this; it will stop after decom­
358 just the first file in the stream. 358 pressing just the first file in the stream.
359 359
360 _b_z_i_p_2_r_e_c_o_v_e_r versions prior to this one, 1.0.2, used 360 _b_z_i_p_2_r_e_c_o_v_e_r versions prior to 1.0.2 used 32‐bit integers
361 32-bit integers to represent bit positions in compressed 361 to represent bit positions in compressed files, so they
362 files, so it could not handle compressed files more than 362 could not handle compressed files more than 512 megabytes
363 512 megabytes long. Version 1.0.2 and above uses 64-bit 363 long. Versions 1.0.2 and above use 64bit ints on some
364 ints on some platforms which support them (GNU supported 364 platforms which support them (GNU supported targets, and
365 targets, and Windows). To establish whether or not 365 Windows). To establish whether or not bzip2recover was
366 bzip2recover was built with such a limitation, run it 366 built with such a limitation, run it without arguments.
367 without arguments. In any event you can build yourself an 367 In any event you can build yourself an unlimited version
368 unlimited version if you can recompile it with MaybeUInt64 368 if you can recompile it with MaybeUInt64 set to be an
369 set to be an unsigned 64-bit integer. 369 unsigned 64bit integer.
370 370
371 371
372 372
373 373
374AAUUTTHHOORR 374AAUUTTHHOORR
375 Julian Seward, jseward@acm.org. 375 Julian Seward, jsewardbzip.org.
376 376
377 http://sources.redhat.com/bzip2 377 http://www.bzip.org
378 378
379 The ideas embodied in _b_z_i_p_2 are due to (at least) the fol 379 The ideas embodied in _b_z_i_p_2 are due to (at least) the fol
380 lowing people: Michael Burrows and David Wheeler (for the 380 lowing people: Michael Burrows and David Wheeler (for the
381 block sorting transformation), David Wheeler (again, for 381 block sorting transformation), David Wheeler (again, for
382 the Huffman coder), Peter Fenwick (for the structured cod 382 the Huffman coder), Peter Fenwick (for the structured cod
383 ing model in the original _b_z_i_p_, and many refinements), and 383 ing model in the original _b_z_i_p_, and many refinements), and
384 Alistair Moffat, Radford Neal and Ian Witten (for the 384 Alistair Moffat, Radford Neal and Ian Witten (for the
385 arithmetic coder in the original _b_z_i_p_)_. I am much 385 arithmetic coder in the original _b_z_i_p_)_. I am much
386 indebted for their help, support and advice. See the man 386 indebted for their help, support and advice. See the man
387 ual in the source distribution for pointers to sources of 387 ual in the source distribution for pointers to sources of
388 documentation. Christian von Roques encouraged me to look 388 documentation. Christian von Roques encouraged me to look
389 for faster sorting algorithms, so as to speed up compres 389 for faster sorting algorithms, so as to speed up compres­
390 sion. Bela Lubkin encouraged me to improve the worst-case 390 sion. Bela Lubkin encouraged me to improve the worst‐case
391 compression performance. The bz* scripts are derived from 391 compression performance. Donna Robinson XMLised the docu­
392 those of GNU gzip. Many people sent patches, helped with 392 mentation. The bz* scripts are derived from those of GNU
393 portability problems, lent machines, gave advice and were 393 gzip. Many people sent patches, helped with portability
394 generally helpful. 394 problems, lent machines, gave advice and were generally
395 helpful.
395 396
396 397
397 398