xref: /linux/lib/lz4/lz4_decompress.c (revision c159dfbdd4fc62fa08f6715d9d6c34d39cf40446)
1 /*
2  * LZ4 - Fast LZ compression algorithm
3  * Copyright (C) 2011 - 2016, Yann Collet.
4  * BSD 2 - Clause License (http://www.opensource.org/licenses/bsd - license.php)
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions are
7  * met:
8  *	* Redistributions of source code must retain the above copyright
9  *	  notice, this list of conditions and the following disclaimer.
10  *	* Redistributions in binary form must reproduce the above
11  * copyright notice, this list of conditions and the following disclaimer
12  * in the documentation and/or other materials provided with the
13  * distribution.
14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
15  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
16  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
17  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
18  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
19  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
20  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
24  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25  * You can contact the author at :
26  *	- LZ4 homepage : http://www.lz4.org
27  *	- LZ4 source repository : https://github.com/lz4/lz4
28  *
29  *	Changed for kernel usage by:
30  *	Sven Schmidt <4sschmid@informatik.uni-hamburg.de>
31  */
32 
33 /*-************************************
34  *	Dependencies
35  **************************************/
36 #include "lz4defs.h"
37 #include <linux/init.h>
38 #include <linux/module.h>
39 #include <linux/kernel.h>
40 #include <linux/unaligned.h>
41 
42 /*-*****************************
43  *	Decompression functions
44  *******************************/
45 
46 #define DEBUGLOG(l, ...) {}	/* disabled */
47 
48 #ifndef assert
49 #define assert(condition) ((void)0)
50 #endif
51 
52 /*
53  * LZ4_decompress_generic() :
54  * This generic decompression function covers all use cases.
55  * It shall be instantiated several times, using different sets of directives.
56  * Note that it is important for performance that this function really get inlined,
57  * in order to remove useless branches during compilation optimization.
58  */
59 static FORCE_INLINE int LZ4_decompress_generic(
60 	 const char * const src,
61 	 char * const dst,
62 	 int srcSize,
63 		/*
64 		 * If endOnInput == endOnInputSize,
65 		 * this value is `dstCapacity`
66 		 */
67 	 int outputSize,
68 	 /* endOnOutputSize, endOnInputSize */
69 	 endCondition_directive endOnInput,
70 	 /* full, partial */
71 	 earlyEnd_directive partialDecoding,
72 	 /* noDict, withPrefix64k, usingExtDict */
73 	 dict_directive dict,
74 	 /* always <= dst, == dst when no prefix */
75 	 const BYTE * const lowPrefix,
76 	 /* only if dict == usingExtDict */
77 	 const BYTE * const dictStart,
78 	 /* note : = 0 if noDict */
79 	 const size_t dictSize
80 	 )
81 {
82 	const BYTE *ip = (const BYTE *) src;
83 	const BYTE * const iend = ip + srcSize;
84 
85 	BYTE *op = (BYTE *) dst;
86 	BYTE * const oend = op + outputSize;
87 	BYTE *cpy;
88 
89 	const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
90 	static const unsigned int inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
91 	static const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};
92 
93 	const int safeDecode = (endOnInput == endOnInputSize);
94 	const int checkOffset = ((safeDecode) && (dictSize < (int)(64 * KB)));
95 
96 	/* Set up the "end" pointers for the shortcut. */
97 	const BYTE *const shortiend = iend -
98 		(endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
99 	const BYTE *const shortoend = oend -
100 		(endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
101 
102 	DEBUGLOG(5, "%s (srcSize:%i, dstSize:%i)", __func__,
103 		 srcSize, outputSize);
104 
105 	/* Special cases */
106 	assert(lowPrefix <= op);
107 	assert(src != NULL);
108 
109 	/* Empty output buffer */
110 	if ((endOnInput) && (unlikely(outputSize == 0)))
111 		return ((srcSize == 1) && (*ip == 0)) ? 0 : -1;
112 
113 	if ((!endOnInput) && (unlikely(outputSize == 0)))
114 		return (*ip == 0 ? 1 : -1);
115 
116 	if ((endOnInput) && unlikely(srcSize == 0))
117 		return -1;
118 
119 	/* Main Loop : decode sequences */
120 	while (1) {
121 		size_t length;
122 		const BYTE *match;
123 		size_t offset;
124 
125 		/* get literal length */
126 		unsigned int const token = *ip++;
127 		length = token>>ML_BITS;
128 
129 		/* ip < iend before the increment */
130 		assert(!endOnInput || ip <= iend);
131 
132 		/*
133 		 * A two-stage shortcut for the most common case:
134 		 * 1) If the literal length is 0..14, and there is enough
135 		 * space, enter the shortcut and copy 16 bytes on behalf
136 		 * of the literals (in the fast mode, only 8 bytes can be
137 		 * safely copied this way).
138 		 * 2) Further if the match length is 4..18, copy 18 bytes
139 		 * in a similar manner; but we ensure that there's enough
140 		 * space in the output for those 18 bytes earlier, upon
141 		 * entering the shortcut (in other words, there is a
142 		 * combined check for both stages).
143 		 *
144 		 * The & in the likely() below is intentionally not && so that
145 		 * some compilers can produce better parallelized runtime code
146 		 */
147 		if ((endOnInput ? length != RUN_MASK : length <= 8)
148 		   /*
149 		    * strictly "less than" on input, to re-enter
150 		    * the loop with at least one byte
151 		    */
152 		   && likely((endOnInput ? ip < shortiend : 1) &
153 			     (op <= shortoend))) {
154 			/* Copy the literals */
155 			LZ4_memcpy(op, ip, endOnInput ? 16 : 8);
156 			op += length; ip += length;
157 
158 			/*
159 			 * The second stage:
160 			 * prepare for match copying, decode full info.
161 			 * If it doesn't work out, the info won't be wasted.
162 			 */
163 			length = token & ML_MASK; /* match length */
164 			offset = LZ4_readLE16(ip);
165 			ip += 2;
166 			match = op - offset;
167 			assert(match <= op); /* check overflow */
168 
169 			/* Do not deal with overlapping matches. */
170 			if ((length != ML_MASK) &&
171 			    (offset >= 8) &&
172 			    (dict == withPrefix64k || match >= lowPrefix)) {
173 				/* Copy the match. */
174 				LZ4_memcpy(op + 0, match + 0, 8);
175 				LZ4_memcpy(op + 8, match + 8, 8);
176 				LZ4_memcpy(op + 16, match + 16, 2);
177 				op += length + MINMATCH;
178 				/* Both stages worked, load the next token. */
179 				continue;
180 			}
181 
182 			/*
183 			 * The second stage didn't work out, but the info
184 			 * is ready. Propel it right to the point of match
185 			 * copying.
186 			 */
187 			goto _copy_match;
188 		}
189 
190 		/* decode literal length */
191 		if (length == RUN_MASK) {
192 			unsigned int s;
193 
194 			if (unlikely(endOnInput ? ip >= iend - RUN_MASK : 0)) {
195 				/* overflow detection */
196 				goto _output_error;
197 			}
198 			do {
199 				s = *ip++;
200 				length += s;
201 			} while (likely(endOnInput
202 				? ip < iend - RUN_MASK
203 				: 1) & (s == 255));
204 
205 			if ((safeDecode)
206 			    && unlikely((uptrval)(op) +
207 					length < (uptrval)(op))) {
208 				/* overflow detection */
209 				goto _output_error;
210 			}
211 			if ((safeDecode)
212 			    && unlikely((uptrval)(ip) +
213 					length < (uptrval)(ip))) {
214 				/* overflow detection */
215 				goto _output_error;
216 			}
217 		}
218 
219 		/* copy literals */
220 		cpy = op + length;
221 		LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);
222 
223 		if (((endOnInput) && ((cpy > oend - MFLIMIT)
224 			|| (ip + length > iend - (2 + 1 + LASTLITERALS))))
225 			|| ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
226 			if (partialDecoding) {
227 				if (cpy > oend) {
228 					/*
229 					 * Partial decoding :
230 					 * stop in the middle of literal segment
231 					 */
232 					cpy = oend;
233 					length = oend - op;
234 				}
235 				if ((endOnInput)
236 					&& (ip + length > iend)) {
237 					/*
238 					 * Error :
239 					 * read attempt beyond
240 					 * end of input buffer
241 					 */
242 					goto _output_error;
243 				}
244 			} else {
245 				if ((!endOnInput)
246 					&& (cpy != oend)) {
247 					/*
248 					 * Error :
249 					 * block decoding must
250 					 * stop exactly there
251 					 */
252 					goto _output_error;
253 				}
254 				if ((endOnInput)
255 					&& ((ip + length != iend)
256 					|| (cpy > oend))) {
257 					/*
258 					 * Error :
259 					 * input must be consumed
260 					 */
261 					goto _output_error;
262 				}
263 			}
264 
265 			/*
266 			 * supports overlapping memory regions; only matters
267 			 * for in-place decompression scenarios
268 			 */
269 			LZ4_memmove(op, ip, length);
270 			ip += length;
271 			op += length;
272 
273 			/* Necessarily EOF when !partialDecoding.
274 			 * When partialDecoding, it is EOF if we've either
275 			 * filled the output buffer or
276 			 * can't proceed with reading an offset for following match.
277 			 */
278 			if (!partialDecoding || (cpy == oend) || (ip >= (iend - 2)))
279 				break;
280 		} else {
281 			/* may overwrite up to WILDCOPYLENGTH beyond cpy */
282 			LZ4_wildCopy(op, ip, cpy);
283 			ip += length;
284 			op = cpy;
285 		}
286 
287 		/* get offset */
288 		offset = LZ4_readLE16(ip);
289 		ip += 2;
290 		match = op - offset;
291 
292 		/* get matchlength */
293 		length = token & ML_MASK;
294 
295 _copy_match:
296 		if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) {
297 			/* Error : offset outside buffers */
298 			goto _output_error;
299 		}
300 
301 		/* costs ~1%; silence an msan warning when offset == 0 */
302 		/*
303 		 * note : when partialDecoding, there is no guarantee that
304 		 * at least 4 bytes remain available in output buffer
305 		 */
306 		if (!partialDecoding) {
307 			assert(oend > op);
308 			assert(oend - op >= 4);
309 
310 			LZ4_write32(op, (U32)offset);
311 		}
312 
313 		if (length == ML_MASK) {
314 			unsigned int s;
315 
316 			do {
317 				s = *ip++;
318 
319 				if ((endOnInput) && (ip > iend - LASTLITERALS))
320 					goto _output_error;
321 
322 				length += s;
323 			} while (s == 255);
324 
325 			if ((safeDecode)
326 				&& unlikely(
327 					(uptrval)(op) + length < (uptrval)op)) {
328 				/* overflow detection */
329 				goto _output_error;
330 			}
331 		}
332 
333 		length += MINMATCH;
334 
335 		/* match starting within external dictionary */
336 		if ((dict == usingExtDict) && (match < lowPrefix)) {
337 			if (unlikely(op + length > oend - LASTLITERALS)) {
338 				/* doesn't respect parsing restriction */
339 				if (!partialDecoding)
340 					goto _output_error;
341 				length = min(length, (size_t)(oend - op));
342 			}
343 
344 			if (length <= (size_t)(lowPrefix - match)) {
345 				/*
346 				 * match fits entirely within external
347 				 * dictionary : just copy
348 				 */
349 				memmove(op, dictEnd - (lowPrefix - match),
350 					length);
351 				op += length;
352 			} else {
353 				/*
354 				 * match stretches into both external
355 				 * dictionary and current block
356 				 */
357 				size_t const copySize = (size_t)(lowPrefix - match);
358 				size_t const restSize = length - copySize;
359 
360 				LZ4_memcpy(op, dictEnd - copySize, copySize);
361 				op += copySize;
362 				if (restSize > (size_t)(op - lowPrefix)) {
363 					/* overlap copy */
364 					BYTE * const endOfMatch = op + restSize;
365 					const BYTE *copyFrom = lowPrefix;
366 
367 					while (op < endOfMatch)
368 						*op++ = *copyFrom++;
369 				} else {
370 					LZ4_memcpy(op, lowPrefix, restSize);
371 					op += restSize;
372 				}
373 			}
374 			continue;
375 		}
376 
377 		/* copy match within block */
378 		cpy = op + length;
379 
380 		/*
381 		 * partialDecoding :
382 		 * may not respect endBlock parsing restrictions
383 		 */
384 		assert(op <= oend);
385 		if (partialDecoding &&
386 		    (cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
387 			size_t const mlen = min(length, (size_t)(oend - op));
388 			const BYTE * const matchEnd = match + mlen;
389 			BYTE * const copyEnd = op + mlen;
390 
391 			if (matchEnd > op) {
392 				/* overlap copy */
393 				while (op < copyEnd)
394 					*op++ = *match++;
395 			} else {
396 				LZ4_memcpy(op, match, mlen);
397 			}
398 			op = copyEnd;
399 			if (op == oend)
400 				break;
401 			continue;
402 		}
403 
404 		if (unlikely(offset < 8)) {
405 			op[0] = match[0];
406 			op[1] = match[1];
407 			op[2] = match[2];
408 			op[3] = match[3];
409 			match += inc32table[offset];
410 			LZ4_memcpy(op + 4, match, 4);
411 			match -= dec64table[offset];
412 		} else {
413 			LZ4_copy8(op, match);
414 			match += 8;
415 		}
416 
417 		op += 8;
418 
419 		if (unlikely(cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
420 			BYTE * const oCopyLimit = oend - (WILDCOPYLENGTH - 1);
421 
422 			if (cpy > oend - LASTLITERALS) {
423 				/*
424 				 * Error : last LASTLITERALS bytes
425 				 * must be literals (uncompressed)
426 				 */
427 				goto _output_error;
428 			}
429 
430 			if (op < oCopyLimit) {
431 				LZ4_wildCopy(op, match, oCopyLimit);
432 				match += oCopyLimit - op;
433 				op = oCopyLimit;
434 			}
435 			while (op < cpy)
436 				*op++ = *match++;
437 		} else {
438 			LZ4_copy8(op, match);
439 			if (length > 16)
440 				LZ4_wildCopy(op + 8, match + 8, cpy);
441 		}
442 		op = cpy; /* wildcopy correction */
443 	}
444 
445 	/* end of decoding */
446 	if (endOnInput) {
447 		/* Nb of output bytes decoded */
448 		return (int) (((char *)op) - dst);
449 	} else {
450 		/* Nb of input bytes read */
451 		return (int) (((const char *)ip) - src);
452 	}
453 
454 	/* Overflow error detected */
455 _output_error:
456 	return (int) (-(((const char *)ip) - src)) - 1;
457 }
458 
459 int LZ4_decompress_safe(const char *source, char *dest,
460 	int compressedSize, int maxDecompressedSize)
461 {
462 	return LZ4_decompress_generic(source, dest,
463 				      compressedSize, maxDecompressedSize,
464 				      endOnInputSize, decode_full_block,
465 				      noDict, (BYTE *)dest, NULL, 0);
466 }
467 
468 int LZ4_decompress_safe_partial(const char *src, char *dst,
469 	int compressedSize, int targetOutputSize, int dstCapacity)
470 {
471 	dstCapacity = min(targetOutputSize, dstCapacity);
472 	return LZ4_decompress_generic(src, dst, compressedSize, dstCapacity,
473 				      endOnInputSize, partial_decode,
474 				      noDict, (BYTE *)dst, NULL, 0);
475 }
476 
477 int LZ4_decompress_fast(const char *source, char *dest, int originalSize)
478 {
479 	return LZ4_decompress_generic(source, dest, 0, originalSize,
480 				      endOnOutputSize, decode_full_block,
481 				      withPrefix64k,
482 				      (BYTE *)dest - 64 * KB, NULL, 0);
483 }
484 
485 /* ===== Instantiate a few more decoding cases, used more than once. ===== */
486 
487 static int LZ4_decompress_safe_withPrefix64k(const char *source, char *dest,
488 				      int compressedSize, int maxOutputSize)
489 {
490 	return LZ4_decompress_generic(source, dest,
491 				      compressedSize, maxOutputSize,
492 				      endOnInputSize, decode_full_block,
493 				      withPrefix64k,
494 				      (BYTE *)dest - 64 * KB, NULL, 0);
495 }
496 
497 static int LZ4_decompress_safe_withSmallPrefix(const char *source, char *dest,
498 					       int compressedSize,
499 					       int maxOutputSize,
500 					       size_t prefixSize)
501 {
502 	return LZ4_decompress_generic(source, dest,
503 				      compressedSize, maxOutputSize,
504 				      endOnInputSize, decode_full_block,
505 				      noDict,
506 				      (BYTE *)dest - prefixSize, NULL, 0);
507 }
508 
509 static int LZ4_decompress_safe_forceExtDict(const char *source, char *dest,
510 					    int compressedSize, int maxOutputSize,
511 					    const void *dictStart, size_t dictSize)
512 {
513 	return LZ4_decompress_generic(source, dest,
514 				      compressedSize, maxOutputSize,
515 				      endOnInputSize, decode_full_block,
516 				      usingExtDict, (BYTE *)dest,
517 				      (const BYTE *)dictStart, dictSize);
518 }
519 
520 static int LZ4_decompress_fast_extDict(const char *source, char *dest,
521 				       int originalSize,
522 				       const void *dictStart, size_t dictSize)
523 {
524 	return LZ4_decompress_generic(source, dest,
525 				      0, originalSize,
526 				      endOnOutputSize, decode_full_block,
527 				      usingExtDict, (BYTE *)dest,
528 				      (const BYTE *)dictStart, dictSize);
529 }
530 
531 /*
532  * The "double dictionary" mode, for use with e.g. ring buffers: the first part
533  * of the dictionary is passed as prefix, and the second via dictStart + dictSize.
534  * These routines are used only once, in LZ4_decompress_*_continue().
535  */
536 static FORCE_INLINE
537 int LZ4_decompress_safe_doubleDict(const char *source, char *dest,
538 				   int compressedSize, int maxOutputSize,
539 				   size_t prefixSize,
540 				   const void *dictStart, size_t dictSize)
541 {
542 	return LZ4_decompress_generic(source, dest,
543 				      compressedSize, maxOutputSize,
544 				      endOnInputSize, decode_full_block,
545 				      usingExtDict, (BYTE *)dest - prefixSize,
546 				      (const BYTE *)dictStart, dictSize);
547 }
548 
549 static FORCE_INLINE
550 int LZ4_decompress_fast_doubleDict(const char *source, char *dest,
551 				   int originalSize, size_t prefixSize,
552 				   const void *dictStart, size_t dictSize)
553 {
554 	return LZ4_decompress_generic(source, dest,
555 				      0, originalSize,
556 				      endOnOutputSize, decode_full_block,
557 				      usingExtDict, (BYTE *)dest - prefixSize,
558 				      (const BYTE *)dictStart, dictSize);
559 }
560 
561 /* ===== streaming decompression functions ===== */
562 
563 int LZ4_setStreamDecode(LZ4_streamDecode_t *LZ4_streamDecode,
564 	const char *dictionary, int dictSize)
565 {
566 	LZ4_streamDecode_t_internal *lz4sd =
567 		&LZ4_streamDecode->internal_donotuse;
568 
569 	lz4sd->prefixSize = (size_t) dictSize;
570 	lz4sd->prefixEnd = (const BYTE *) dictionary + dictSize;
571 	lz4sd->externalDict = NULL;
572 	lz4sd->extDictSize	= 0;
573 	return 1;
574 }
575 
576 /*
577  * *_continue() :
578  * These decoding functions allow decompression of multiple blocks
579  * in "streaming" mode.
580  * Previously decoded blocks must still be available at the memory
581  * position where they were decoded.
582  * If it's not possible, save the relevant part of
583  * decoded data into a safe buffer,
584  * and indicate where it stands using LZ4_setStreamDecode()
585  */
586 int LZ4_decompress_safe_continue(LZ4_streamDecode_t *LZ4_streamDecode,
587 	const char *source, char *dest, int compressedSize, int maxOutputSize)
588 {
589 	LZ4_streamDecode_t_internal *lz4sd =
590 		&LZ4_streamDecode->internal_donotuse;
591 	int result;
592 
593 	if (lz4sd->prefixSize == 0) {
594 		/* The first call, no dictionary yet. */
595 		assert(lz4sd->extDictSize == 0);
596 		result = LZ4_decompress_safe(source, dest,
597 			compressedSize, maxOutputSize);
598 		if (result <= 0)
599 			return result;
600 		lz4sd->prefixSize = result;
601 		lz4sd->prefixEnd = (BYTE *)dest + result;
602 	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
603 		/* They're rolling the current segment. */
604 		if (lz4sd->prefixSize >= 64 * KB - 1)
605 			result = LZ4_decompress_safe_withPrefix64k(source, dest,
606 				compressedSize, maxOutputSize);
607 		else if (lz4sd->extDictSize == 0)
608 			result = LZ4_decompress_safe_withSmallPrefix(source,
609 				dest, compressedSize, maxOutputSize,
610 				lz4sd->prefixSize);
611 		else
612 			result = LZ4_decompress_safe_doubleDict(source, dest,
613 				compressedSize, maxOutputSize,
614 				lz4sd->prefixSize,
615 				lz4sd->externalDict, lz4sd->extDictSize);
616 		if (result <= 0)
617 			return result;
618 		lz4sd->prefixSize += result;
619 		lz4sd->prefixEnd  += result;
620 	} else {
621 		/*
622 		 * The buffer wraps around, or they're
623 		 * switching to another buffer.
624 		 */
625 		lz4sd->extDictSize = lz4sd->prefixSize;
626 		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
627 		result = LZ4_decompress_safe_forceExtDict(source, dest,
628 			compressedSize, maxOutputSize,
629 			lz4sd->externalDict, lz4sd->extDictSize);
630 		if (result <= 0)
631 			return result;
632 		lz4sd->prefixSize = result;
633 		lz4sd->prefixEnd  = (BYTE *)dest + result;
634 	}
635 
636 	return result;
637 }
638 
639 int LZ4_decompress_fast_continue(LZ4_streamDecode_t *LZ4_streamDecode,
640 	const char *source, char *dest, int originalSize)
641 {
642 	LZ4_streamDecode_t_internal *lz4sd = &LZ4_streamDecode->internal_donotuse;
643 	int result;
644 
645 	if (lz4sd->prefixSize == 0) {
646 		assert(lz4sd->extDictSize == 0);
647 		result = LZ4_decompress_fast(source, dest, originalSize);
648 		if (result <= 0)
649 			return result;
650 		lz4sd->prefixSize = originalSize;
651 		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
652 	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
653 		if (lz4sd->prefixSize >= 64 * KB - 1 ||
654 		    lz4sd->extDictSize == 0)
655 			result = LZ4_decompress_fast(source, dest,
656 						     originalSize);
657 		else
658 			result = LZ4_decompress_fast_doubleDict(source, dest,
659 				originalSize, lz4sd->prefixSize,
660 				lz4sd->externalDict, lz4sd->extDictSize);
661 		if (result <= 0)
662 			return result;
663 		lz4sd->prefixSize += originalSize;
664 		lz4sd->prefixEnd  += originalSize;
665 	} else {
666 		lz4sd->extDictSize = lz4sd->prefixSize;
667 		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
668 		result = LZ4_decompress_fast_extDict(source, dest,
669 			originalSize, lz4sd->externalDict, lz4sd->extDictSize);
670 		if (result <= 0)
671 			return result;
672 		lz4sd->prefixSize = originalSize;
673 		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
674 	}
675 	return result;
676 }
677 
678 int LZ4_decompress_safe_usingDict(const char *source, char *dest,
679 				  int compressedSize, int maxOutputSize,
680 				  const char *dictStart, int dictSize)
681 {
682 	if (dictSize == 0)
683 		return LZ4_decompress_safe(source, dest,
684 					   compressedSize, maxOutputSize);
685 	if (dictStart+dictSize == dest) {
686 		if (dictSize >= 64 * KB - 1)
687 			return LZ4_decompress_safe_withPrefix64k(source, dest,
688 				compressedSize, maxOutputSize);
689 		return LZ4_decompress_safe_withSmallPrefix(source, dest,
690 			compressedSize, maxOutputSize, dictSize);
691 	}
692 	return LZ4_decompress_safe_forceExtDict(source, dest,
693 		compressedSize, maxOutputSize, dictStart, dictSize);
694 }
695 
696 int LZ4_decompress_fast_usingDict(const char *source, char *dest,
697 				  int originalSize,
698 				  const char *dictStart, int dictSize)
699 {
700 	if (dictSize == 0 || dictStart + dictSize == dest)
701 		return LZ4_decompress_fast(source, dest, originalSize);
702 
703 	return LZ4_decompress_fast_extDict(source, dest, originalSize,
704 		dictStart, dictSize);
705 }
706 
707 #ifndef STATIC
708 EXPORT_SYMBOL(LZ4_decompress_safe);
709 EXPORT_SYMBOL(LZ4_decompress_safe_partial);
710 EXPORT_SYMBOL(LZ4_decompress_fast);
711 EXPORT_SYMBOL(LZ4_setStreamDecode);
712 EXPORT_SYMBOL(LZ4_decompress_safe_continue);
713 EXPORT_SYMBOL(LZ4_decompress_fast_continue);
714 EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
715 EXPORT_SYMBOL(LZ4_decompress_fast_usingDict);
716 
717 MODULE_LICENSE("Dual BSD/GPL");
718 MODULE_DESCRIPTION("LZ4 decompressor");
719 #endif
720