aboutsummaryrefslogtreecommitdiff
path: root/lib/decompress_bunzip2.c
blob: d3dc9f2beb27f2d8cfca19b7ab657494528cc5a3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
/* vi: set sw = 4 ts = 4: */
/*	Small bzip2 deflate implementation, by Rob Landley (rob@landley.net).

	Based on bzip2 decompression code by Julian R Seward (jseward@acm.org),
	which also acknowledges contributions by Mike Burrows, David Wheeler,
	Peter Fenwick, Alistair Moffat, Radford Neal, Ian H. Witten,
	Robert Sedgewick, and Jon L. Bentley.

	This code is licensed under the LGPLv2:
		LGPL (http://www.gnu.org/copyleft/lgpl.html
*/

/*
	Size and speed optimizations by Manuel Novoa III  (mjn3@codepoet.org).

	More efficient reading of Huffman codes, a streamlined read_bunzip()
	function, and various other tweaks.  In (limited) tests, approximately
	20% faster than bzcat on x86 and about 10% faster on arm.

	Note that about 2/3 of the time is spent in read_unzip() reversing
	the Burrows-Wheeler transformation.  Much of that time is delay
	resulting from cache misses.

	I would ask that anyone benefiting from this work, especially those
	using it in commercial products, consider making a donation to my local
	non-profit hospice organization in the name of the woman I loved, who
	passed away Feb. 12, 2003.

		In memory of Toni W. Hagan

		Hospice of Acadiana, Inc.
		2600 Johnston St., Suite 200
		Lafayette, LA 70503-3240

		Phone (337) 232-1234 or 1-800-738-2226
		Fax   (337) 232-1297

		http://www.hospiceacadiana.com/

	Manuel
 */

/*
	Made it fit for running in Linux Kernel by Alain Knaff (alain@knaff.lu)
*/


#ifdef STATIC
#define PREBOOT
#else
#include <linux/decompress/bunzip2.h>
#endif /* STATIC */

#include <linux/decompress/mm.h>
#include <linux/slab.h>

#ifndef INT_MAX
#define INT_MAX 0x7fffffff
#endif

/* Constants for Huffman coding */
#define MAX_GROUPS		6
#define GROUP_SIZE   		50	/* 64 would have been more efficient */
#define MAX_HUFCODE_BITS 	20	/* Longest Huffman code allowed */
#define MAX_SYMBOLS 		258	/* 256 literals + RUNA + RUNB */
#define SYMBOL_RUNA		0
#define SYMBOL_RUNB		1

/* Status return values */
#define RETVAL_OK			0
#define RETVAL_LAST_BLOCK		(-1)
#define RETVAL_NOT_BZIP_DATA		(-2)
#define RETVAL_UNEXPECTED_INPUT_EOF	(-3)
#define RETVAL_UNEXPECTED_OUTPUT_EOF	(-4)
#define RETVAL_DATA_ERROR		(-5)
#define RETVAL_OUT_OF_MEMORY		(-6)
#define RETVAL_OBSOLETE_INPUT		(-7)

/* Other housekeeping constants */
#define BZIP2_IOBUF_SIZE		4096

/* This is what we know about each Huffman coding group */
struct group_data {
	/* We have an extra slot at the end of limit[] for a sentinal value. */
	int limit[MAX_HUFCODE_BITS+1];
	int base[MAX_HUFCODE_BITS];
	int permute[MAX_SYMBOLS];
	int minLen, maxLen;
};

/* Structure holding all the housekeeping data, including IO buffers and
   memory that persists between calls to bunzip */
struct bunzip_data {
	/* State for interrupting output loop */
	int writeCopies, writePos, writeRunCountdown, writeCount, writeCurrent;
	/* I/O tracking data (file handles, buffers, positions, etc.) */
	int (*fill)(void*, unsigned int);
	int inbufCount, inbufPos /*, outbufPos*/;
	unsigned char *inbuf /*,*outbuf*/;
	unsigned int inbufBitCount, inbufBits;
	/* The CRC values stored in the block header and calculated from the
	data */
	unsigned int crc32Table[256], headerCRC, totalCRC, writeCRC;
	/* Intermediate buffer and its size (in bytes) */
	unsigned int *dbuf, dbufSize;
	/* These things are a bit too big to go on the stack */
	unsigned char selectors[32768];		/* nSelectors = 15 bits */
	struct group_data groups[MAX_GROUPS];	/* Huffman coding tables */
	int io_error;			/* non-zero if we have IO error */
};


/* Return the next nnn bits of input.  All reads from the compressed input
   are done through this function.  All reads are big endian */
static unsigned int INIT get_bits(struct bunzip_data *bd, char bits_wanted)
{
	unsigned int bits = 0;

	/* If we need to get more data from the byte buffer, do so.
	   (Loop getting one byte at a time to enforce endianness and avoid
	   unaligned access.) */
	while (bd->inbufBitCount < bits_wanted) {
		/* If we need to read more data from file into byte buffer, do
		   so */
		if (bd->inbufPos == bd->inbufCount) {
			if (bd->io_error)
				return 0;
			bd->inbufCount = bd->fill(bd->inbuf, BZIP2_IOBUF_SIZE);
			if (bd->inbufCount <= 0) {
				bd->io_error = RETVAL_UNEXPECTED_INPUT_EOF;
				return 0;
			}
			bd->inbufPos = 0;
		}
		/* Avoid 32-bit overflow (dump bit buffer to top of output) */
		if (bd->inbufBitCount >= 24) {
			bits = bd->inbufBits&((1 << bd->inbufBitCount)-1);
			bits_wanted -= bd->inbufBitCount;
			bits <<= bits_wanted;
			bd->inbufBitCount = 0;
		}
		/* Grab next 8 bits of input from buffer. */
		bd->inbufBits = (bd->inbufBits << 8)|bd->inbuf[bd->inbufPos++];
		bd->inbufBitCount += 8;
	}
	/* Calculate result */
	bd->inbufBitCount -= bits_wanted;
	bits |= (bd->inbufBits >> bd->inbufBitCount)&((1 << bits_wanted)-1);

	return bits;
}

/* Unpacks the next block and sets up for the inverse burrows-wheeler step. */

static int INIT get_next_block(struct bunzip_data *bd)
{
	struct group_data *hufGroup = NULL;
	int *base = NULL;
	int *limit = NULL;
	int dbufCount, nextSym, dbufSize, groupCount, selector,
		i, j, k, t, runPos, symCount, symTotal, nSelectors,
		byteCount[256];
	unsigned char uc, symToByte[256], mtfSymbol[256], *selectors;
	unsigned int *dbuf, origPtr;

	dbuf = bd->dbuf;
	dbufSize = bd->dbufSize;
	selectors = bd->selectors;

	/* Read in header signature and CRC, then validate signature.
	   (last block signature means CRC is for whole file, return now) */
	i = get_bits(bd, 24);
	j = get_bits(bd, 24);
	bd->headerCRC = get_bits(bd, 32);
	if ((i == 0x177245) && (j == 0x385090))
		return RETVAL_LAST_BLOCK;
	if ((i != 0x314159) || (j != 0x265359))
		return RETVAL_NOT_BZIP_DATA;
	/* We can add support for blockRandomised if anybody complains.
	   There was some code for this in busybox 1.0.0-pre3, but nobody ever
	   noticed that it didn't actually work. */
	if (get_bits(bd, 1))
		return RETVAL_OBSOLETE_INPUT;
	origPtr = get_bits(bd, 24);
	if (origPtr > dbufSize)
		return RETVAL_DATA_ERROR;
	/* mapping table: if some byte values are never used (encoding things
	   like ascii text), the compression code removes the gaps to have fewer
	   symbols to deal with, and writes a sparse bitfield indicating which
	   values were present.  We make a translation table to convert the
	   symbols back to the corresponding bytes. */
	t = get_bits(bd, 16);
	symTotal = 0;
	for (i = 0; i < 16; i++) {
		if (t&(1 << (15-i))) {
			k = get_bits(bd, 16);
			for (j = 0; j < 16; j++)
				if (k&(1 << (15-j)))
					symToByte[symTotal++] = (16*i)+j;
		}
	}
	/* How many different Huffman coding groups does this block use? */
	groupCount = get_bits(bd, 3);
	if (groupCount < 2 || groupCount > MAX_GROUPS)
		return RETVAL_DATA_ERROR;
	/* nSelectors: Every GROUP_SIZE many symbols we select a new
	   Huffman coding group.  Read in the group selector list,
	   which is stored as MTF encoded bit runs.  (MTF = Move To
	   Front, as each value is used it's moved to the start of the
	   list.) */
	nSelectors = get_bits(bd, 15);
	if (!nSelectors)
		return RETVAL_DATA_ERROR;
	for (i = 0; i < groupCount; i++)
		mtfSymbol[i] = i;
	for (i = 0; i < nSelectors; i++) {
		/* Get next value */
		for (j = 0; get_bits(bd, 1); j++)
			if (j >= groupCount)
				return RETVAL_DATA_ERROR;
		/* Decode MTF to get the next selector */
		uc = mtfSymbol[j];
		for (; j; j--)
			mtfSymbol[j] = mtfSymbol[j-1];
		mtfSymbol[0] = selectors[i] = uc;
	}
	/* Read the Huffman coding tables for each group, which code
	   for symTotal literal symbols, plus two run symbols (RUNA,
	   RUNB) */
	symCount = symTotal+2;
	for (j = 0; j < groupCount; j++) {
		unsigned char length[MAX_SYMBOLS], temp[MAX_HUFCODE_BITS+1];
		int	minLen,	maxLen, pp;
		/* Read Huffman code lengths for each symbol.  They're
		   stored in a way similar to mtf; record a starting
		   value for the first symbol, and an offset from the
		   previous value for everys symbol after that.
		   (Subtracting 1 before the loop and then adding it
		   back at the end is an optimization that makes the
		   test inside the loop simpler: symbol length 0
		   becomes negative, so an unsigned inequality catches
		   it.) */
		t = get_bits(bd, 5)-1;
		for (i = 0; i < symCount; i++) {
			for (;;) {
				if (((unsigned)t) > (MAX_HUFCODE_BITS-1))
					return RETVAL_DATA_ERROR;

				/* If first bit is 0, stop.  Else
				   second bit indicates whether to
				   increment or decrement the value.
				   Optimization: grab 2 bits and unget
				   the second if the first was 0. */

				k = get_bits(bd, 2);
				if (k < 2) {
					bd->inbufBitCount++;
					break;
				}
				/* Add one if second bit 1, else
				 * subtract 1.  Avoids if/else */
				t += (((k+1)&2)-1);
			}
			/* Correct for the initial -1, to get the
			 * final symbol length */
			length[i] = t+1;
		}
		/* Find largest and smallest lengths in this group */
		minLen = maxLen = length[0];

		for (i = 1; i < symCount; i++) {
			if (length[i] > maxLen)
				maxLen = length[i];
			else if (length[i] < minLen)
				minLen = length[i];
		}

		/* Calculate permute[], base[], and limit[] tables from
		 * length[].
		 *
		 * permute[] is the lookup table for converting
		 * Huffman coded symbols into decoded symbols.  base[]
		 * is the amount to subtract from the value of a
		 * Huffman symbol of a given length when using
		 * permute[].
		 *
		 * limit[] indicates the largest numerical value a
		 * symbol with a given number of bits can have.  This
		 * is how the Huffman codes can vary in length: each
		 * code with a value > limit[length] needs another
		 * bit.
		 */
		hufGroup = bd->groups+j;
		hufGroup->minLen = minLen;
		hufGroup->maxLen = maxLen;
		/* Note that minLen can't be smaller than 1, so we
		   adjust the base and limit array pointers so we're
		   not always wasting the first entry.  We do this
		   again when using them (during symbol decoding).*/
		base = hufGroup->base-1;
		limit = hufGroup->limit-1;
		/* Calculate permute[].  Concurently, initialize
		 * temp[] and limit[]. */
		pp = 0;
		for (i = minLen; i <= maxLen; i++) {
			temp[i] = limit[i] = 0;
			for (t = 0; t < symCount; t++)
				if (length[t] == i)
					hufGroup->permute[pp++] = t;
		}
		/* Count symbols coded for at each bit length */
		for (i = 0; i < symCount; i++)
			temp[length[i]]++;
		/* Calculate limit[] (the largest symbol-coding value
		 *at each bit length, which is (previous limit <<
		 *1)+symbols at this level), and base[] (number of
		 *symbols to ignore at each bit length, which is limit
		 *minus the cumulative count of symbols coded for
		 *already). */
		pp = t = 0;
		for (i = minLen; i < maxLen; i++) {
			pp += temp[i];
			/* We read the largest possible symbol size
			   and then unget bits after determining how
			   many we need, and those extra bits could be
			   set to anything.  (They're noise from
			   future symbols.)  At each level we're
			   really only interested in the first few
			   bits, so here we set all the trailing
			   to-be-ignored bits to 1 so they don't
			   affect the value > limit[length]
			   comparison. */
			limit[i] = (pp << (maxLen - i)) - 1;
			pp <<= 1;
			base[i+1] = pp-(t += temp[i]);
		}
		limit[maxLen+1] = INT_MAX; /* Sentinal value for
					    * reading next sym. */
		limit[maxLen] = pp+temp[maxLen]-1;
		base[minLen] = 0;
	}
	/* We've finished reading and digesting the block header.  Now
	   read this block's Huffman coded symbols from the file and
	   undo the Huffman coding and run length encoding, saving the
	   result into dbuf[dbufCount++] = uc */

	/* Initialize symbol occurrence counters and symbol Move To
	 * Front table */
	for (i = 0; i < 256; i++) {
		byteCount[i] = 0;
		mtfSymbol[i] = (unsigned char)i;
	}
	/* Loop through compressed symbols. */
	runPos = dbufCount = symCount = selector = 0;
	for (;;) {
		/* Determine which Huffman coding group to use. */
		if (!(symCount--)) {
			symCount = GROUP_SIZE-1;
			if (selector >= nSelectors)
				return RETVAL_DATA_ERROR;
			hufGroup = bd->groups+selectors[selector++];
			base = hufGroup->base-1;
			limit = hufGroup->limit-1;
		}
		/* Read next Huffman-coded symbol. */
		/* Note: It is far cheaper to read maxLen bits and
		   back up than it is to read minLen bits and then an
		   additional bit at a time, testing as we go.
		   Because there is a trailing last block (with file
		   CRC), there is no danger of the overread causing an
		   unexpected EOF for a valid compressed file.  As a
		   further optimization, we do the read inline
		   (falling back to a call to get_bits if the buffer
		   runs dry).  The following (up to got_huff_bits:) is
		   equivalent to j = get_bits(bd, hufGroup->maxLen);
		 */
		while (bd->inbufBitCount < hufGroup->maxLen) {
			if (bd->inbufPos == bd->inbufCount) {
				j = get_bits(bd, hufGroup->maxLen);
				goto got_huff_bits;
			}
			bd->inbufBits =
				(bd->inbufBits << 8)|bd->inbuf[bd->inbufPos++];
			bd->inbufBitCount += 8;
		};
		bd->inbufBitCount -= hufGroup->maxLen;
		j = (bd->inbufBits >> bd->inbufBitCount)&
			((1 << hufGroup->maxLen)-1);
got_huff_bits:
		/* Figure how how many bits are in next symbol and
		 * unget extras */
		i = hufGroup->minLen;
		while (j > limit[i])
			++i;
		bd->inbufBitCount += (hufGroup->maxLen - i);
		/* Huffman decode value to get nextSym (with bounds checking) */
		if ((i > hufGroup->maxLen)
			|| (((unsigned)(j = (j>>(hufGroup->maxLen-i))-base[i]))
				>= MAX_SYMBOLS))
			return RETVAL_DATA_ERROR;
		nextSym = hufGroup->permute[j];
		/* We have now decoded the symbol, which indicates
		   either a new literal byte, or a repeated run of the
		   most recent literal byte.  First, check if nextSym
		   indicates a repeated run, and if so loop collecting
		   how many times to repeat the last literal. */
		if (((unsigned)nextSym) <= SYMBOL_RUNB) { /* RUNA or RUNB */
			/* If this is the start of a new run, zero out
			 * counter */
			if (!runPos) {
				runPos = 1;
				t = 0;
			}
			/* Neat trick that saves 1 symbol: instead of
			   or-ing 0 or 1 at each bit position, add 1
			   or 2 instead.  For example, 1011 is 1 << 0
			   + 1 << 1 + 2 << 2.  1010 is 2 << 0 + 2 << 1
			   + 1 << 2.  You can make any bit pattern
			   that way using 1 less symbol than the basic
			   or 0/1 method (except all bits 0, which
			   would use no symbols, but a run of length 0
			   doesn't mean anything in this context).
			   Thus space is saved. */
			t += (runPos << nextSym);
			/* +runPos if RUNA; +2*runPos if RUNB */

			runPos <<= 1;
			continue;
		}
		/* When we hit the first non-run symbol after a run,
		   we now know how many times to repeat the last
		   literal, so append that many copies to our buffer
		   of decoded symbols (dbuf) now.  (The last literal
		   used is the one at the head of the mtfSymbol
		   array.) */
		if (runPos) {
			runPos = 0;
			if (dbufCount+t >= dbufSize)
				return RETVAL_DATA_ERROR;

			uc = symToByte[mtfSymbol[0]];
			byteCount[uc] += t;
			while (t--)
				dbuf[dbufCount++] = uc;
		}
		/* Is this the terminating symbol? */
		if (nextSym > symTotal)
			break;
		/* At this point, nextSym indicates a new literal
		   character.  Subtract one to get the position in the
		   MTF array at which this literal is currently to be
		   found.  (Note that the result can't be -1 or 0,
		   because 0 and 1 are RUNA and RUNB.  But another
		   instance of the first symbol in the mtf array,
		   position 0, would have been handled as part of a
		   run above.  Therefore 1 unused mtf position minus 2
		   non-literal nextSym values equals -1.) */
		if (dbufCount >= dbufSize)
			return RETVAL_DATA_ERROR;
		i = nextSym - 1;
		uc = mtfSymbol[i];
		/* Adjust the MTF array.  Since we typically expect to
		 *move only a small number of symbols, and are bound
		 *by 256 in any case, using memmove here would
		 *typically be bigger and slower due to function call
		 *overhead and other assorted setup costs. */
		do {
			mtfSymbol[i] = mtfSymbol[i-1];
		} while (--i);
		mtfSymbol[0] = uc;
		uc = symToByte[uc];
		/* We have our literal byte.  Save it into dbuf. */
		byteCount[uc]++;
		dbuf[dbufCount++] = (unsigned int)uc;
	}
	/* At this point, we've read all the Huffman-coded symbols
	   (and repeated runs) for this block from the input stream,
	   and decoded them into the intermediate buffer.  There are
	   dbufCount many decoded bytes in dbuf[].  Now undo the
	   Burrows-Wheeler transform on dbuf.  See
	   http://dogma.net/markn/articles/bwt/bwt.htm
	 */
	/* Turn byteCount into cumulative occurrence counts of 0 to n-1. */
	j = 0;
	for (i = 0; i < 256; i++) {
		k = j+byteCount[i];
		byteCount[i] = j;
		j = k;
	}
	/* Figure out what order dbuf would be in if we sorted it. */
	for (i = 0; i < dbufCount; i++) {
		uc = (unsigned char)(dbuf[i] & 0xff);
		dbuf[byteCount[uc]] |= (i << 8);
		byteCount[uc]++;
	}
	/* Decode first byte by hand to initialize "previous" byte.
	   Note that it doesn't get output, and if the first three
	   characters are identical it doesn't qualify as a run (hence
	   writeRunCountdown = 5). */
	if (dbufCount) {
		if (origPtr >= dbufCount)
			return RETVAL_DATA_ERROR;
		bd->writePos = dbuf[origPtr];
		bd->writeCurrent = (unsigned char)(bd->writePos&0xff);
		bd->writePos >>= 8;
		bd->writeRunCountdown = 5;
	}
	bd->writeCount = dbufCount;

	return RETVAL_OK;
}

/* Undo burrows-wheeler transform on intermediate buffer to produce output.
   If start_bunzip was initialized with out_fd =-1, then up to len bytes of
   data are written to outbuf.  Return value is number of bytes written or
   error (all errors are negative numbers).  If out_fd!=-1, outbuf and len
   are ignored, data is written to out_fd and return is RETVAL_OK or error.
*/

static int INIT read_bunzip(struct bunzip_data *bd, char *outbuf, int len)
{
	const unsigned int *dbuf;
	int pos, xcurrent, previous, gotcount;

	/* If last read was short due to end of file, return last block now */
	if (bd->writeCount < 0)
		return bd->writeCount;

	gotcount = 0;
	dbuf = bd->dbuf;
	pos = bd->writePos;
	xcurrent = bd->writeCurrent;

	/* We will always have pending decoded data to write into the output
	   buffer unless this is the very first call (in which case we haven't
	   Huffman-decoded a block into the intermediate buffer yet). */

	if (bd->writeCopies) {
		/* Inside the loop, writeCopies means extra copies (beyond 1) */
		--bd->writeCopies;
		/* Loop outputting bytes */
		for (;;) {
			/* If the output buffer is full, snapshot
			 * state and return */
			if (gotcount >= len) {
				bd->writePos = pos;
				bd->writeCurrent = xcurrent;
				bd->writeCopies++;
				return len;
			}
			/* Write next byte into output buffer, updating CRC */
			outbuf[gotcount++] = xcurrent;
			bd->writeCRC = (((bd->writeCRC) << 8)
				^bd->crc32Table[((bd->writeCRC) >> 24)
				^xcurrent]);
			/* Loop now if we're outputting multiple
			 * copies of this byte */
			if (bd->writeCopies) {
				--bd->writeCopies;
				continue;
			}
decode_next_byte:
			if (!bd->writeCount--)
				break;
			/* Follow sequence vector to undo
			 * Burrows-Wheeler transform */
			previous = xcurrent;
			pos = dbuf[pos];
			xcurrent = pos&0xff;
			pos >>= 8;
			/* After 3 consecutive copies of the same
			   byte, the 4th is a repeat count.  We count
			   down from 4 instead *of counting up because
			   testing for non-zero is faster */
			if (--bd->writeRunCountdown) {
				if (xcurrent != previous)
					bd->writeRunCountdown = 4;
			} else {
				/* We have a repeated run, this byte
				 * indicates the count */
				bd->writeCopies = xcurrent;
				xcurrent = previous;
				bd->writeRunCountdown = 5;
				/* Sometimes there are just 3 bytes
				 * (run length 0) */
				if (!bd->writeCopies)
					goto decode_next_byte;
				/* Subtract the 1 copy we'd output
				 * anyway to get extras */
				--bd->writeCopies;
			}
		}
		/* Decompression of this block completed successfully */
		bd->writeCRC = ~bd->writeCRC;
		bd->totalCRC = ((bd->totalCRC << 1) |
				(bd->totalCRC >> 31)) ^ bd->writeCRC;
		/* If this block had a CRC error, force file level CRC error. */
		if (bd->writeCRC != bd->headerCRC) {
			bd->totalCRC = bd->headerCRC+1;
			return RETVAL_LAST_BLOCK;
		}
	}

	/* Refill the intermediate buffer by Huffman-decoding next
	 * block of input */
	/* (previous is just a convenient unused temp variable here) */
	previous = get_next_block(bd);
	if (previous) {
		bd->writeCount = previous;
		return (previous != RETVAL_LAST_BLOCK) ? previous : gotcount;
	}
	bd->writeCRC = 0xffffffffUL;
	pos = bd->writePos;
	xcurrent = bd->writeCurrent;
	goto decode_next_byte;
}

static int INIT nofill(void *buf, unsigned int len)
{
	return -1;
}

/* Allocate the structure, read file header.  If in_fd ==-1, inbuf must contain
   a complete bunzip file (len bytes long).  If in_fd!=-1, inbuf and len are
   ignored, and data is read from file handle into temporary buffer. */
static int INIT start_bunzip(struct bunzip_data **bdp, void *inbuf, int len,
			     int (*fill)(void*, unsigned int))
{
	struct bunzip_data *bd;
	unsigned int i, j, c;
	const unsigned int BZh0 =
		(((unsigned int)'B') << 24)+(((unsigned int)'Z') << 16)
		+(((unsigned int)'h') << 8)+(unsigned int)'0';

	/* Figure out how much data to allocate */
	i = sizeof(struct bunzip_data);

	/* Allocate bunzip_data.  Most fields initialize to zero. */
	bd = *bdp = malloc(i);
	memset(bd, 0, sizeof(struct bunzip_data));
	/* Setup input buffer */
	bd->inbuf = inbuf;
	bd->inbufCount = len;
	if (fill != NULL)
		bd->fill = fill;
	else
		bd->fill = nofill;

	/* Init the CRC32 table (big endian) */
	for (i = 0; i < 256; i++) {
		c = i << 24;
		for (j = 8; j; j--)
			c = c&0x80000000 ? (c << 1)^0x04c11db7 : (c << 1);
		bd->crc32Table[i] = c;
	}

	/* Ensure that file starts with "BZh['1'-'9']." */
	i = get_bits(bd, 32);
	if (((unsigned int)(i-BZh0-1)) >= 9)
		return RETVAL_NOT_BZIP_DATA;

	/* Fourth byte (ascii '1'-'9'), indicates block size in units of 100k of
	   uncompressed data.  Allocate intermediate buffer for block. */
	bd->dbufSize = 100000*(i-BZh0);

	bd->dbuf = large_malloc(bd->dbufSize * sizeof(int));
	return RETVAL_OK;
}

/* Example usage: decompress src_fd to dst_fd.  (Stops at end of bzip2 data,
   not end of file.) */
STATIC int INIT bunzip2(unsigned char *buf, int len,
			int(*fill)(void*, unsigned int),
			int(*flush)(void*, unsigned int),
			unsigned char *outbuf,
			int *pos,
			void(*error_fn)(char *x))
{
	struct bunzip_data *bd;
	int i = -1;
	unsigned char *inbuf;

	set_error_fn(error_fn);
	if (flush)
		outbuf = malloc(BZIP2_IOBUF_SIZE);

	if (!outbuf) {
		error("Could not allocate output bufer");
		return -1;
	}
	if (buf)
		inbuf = buf;
	else
		inbuf = malloc(BZIP2_IOBUF_SIZE);
	if (!inbuf) {
		error("Could not allocate input bufer");
		goto exit_0;
	}
	i = start_bunzip(&bd, inbuf, len, fill);
	if (!i) {
		for (;;) {
			i = read_bunzip(bd, outbuf, BZIP2_IOBUF_SIZE);
			if (i <= 0)
				break;
			if (!flush)
				outbuf += i;
			else
				if (i != flush(outbuf, i)) {
					i = RETVAL_UNEXPECTED_OUTPUT_EOF;
					break;
				}
		}
	}
	/* Check CRC and release memory */
	if (i == RETVAL_LAST_BLOCK) {
		if (bd->headerCRC != bd->totalCRC)
			error("Data integrity error when decompressing.");
		else
			i = RETVAL_OK;
	} else if (i == RETVAL_UNEXPECTED_OUTPUT_EOF) {
		error("Compressed file ends unexpectedly");
	}
	if (bd->dbuf)
		large_free(bd->dbuf);
	if (pos)
		*pos = bd->inbufPos;
	free(bd);
	if (!buf)
		free(inbuf);
exit_0:
	if (flush)
		free(outbuf);
	return i;
}

#ifdef PREBOOT
STATIC int INIT decompress(unsigned char *buf, int len,
			int(*fill)(void*, unsigned int),
			int(*flush)(void*, unsigned int),
			unsigned char *outbuf,
			int *pos,
			void(*error_fn)(char *x))
{
	return bunzip2(buf, len - 4, fill, flush, outbuf, pos, error_fn);
}
#endif