xref: /openbmc/linux/lib/lz4/lz4_decompress.c (revision 6c33a6f4)
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 <linux/lz4.h>
37 #include "lz4defs.h"
38 #include <linux/init.h>
39 #include <linux/module.h>
40 #include <linux/kernel.h>
41 #include <asm/unaligned.h>
42 
43 /*-*****************************
44  *	Decompression functions
45  *******************************/
46 
47 #define DEBUGLOG(l, ...) {}	/* disabled */
48 
49 #ifndef assert
50 #define assert(condition) ((void)0)
51 #endif
52 
53 /*
54  * LZ4_decompress_generic() :
55  * This generic decompression function covers all use cases.
56  * It shall be instantiated several times, using different sets of directives.
57  * Note that it is important for performance that this function really get inlined,
58  * in order to remove useless branches during compilation optimization.
59  */
60 static FORCE_INLINE int LZ4_decompress_generic(
61 	 const char * const src,
62 	 char * const dst,
63 	 int srcSize,
64 		/*
65 		 * If endOnInput == endOnInputSize,
66 		 * this value is `dstCapacity`
67 		 */
68 	 int outputSize,
69 	 /* endOnOutputSize, endOnInputSize */
70 	 endCondition_directive endOnInput,
71 	 /* full, partial */
72 	 earlyEnd_directive partialDecoding,
73 	 /* noDict, withPrefix64k, usingExtDict */
74 	 dict_directive dict,
75 	 /* always <= dst, == dst when no prefix */
76 	 const BYTE * const lowPrefix,
77 	 /* only if dict == usingExtDict */
78 	 const BYTE * const dictStart,
79 	 /* note : = 0 if noDict */
80 	 const size_t dictSize
81 	 )
82 {
83 	const BYTE *ip = (const BYTE *) src;
84 	const BYTE * const iend = ip + srcSize;
85 
86 	BYTE *op = (BYTE *) dst;
87 	BYTE * const oend = op + outputSize;
88 	BYTE *cpy;
89 
90 	const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
91 	static const unsigned int inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
92 	static const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};
93 
94 	const int safeDecode = (endOnInput == endOnInputSize);
95 	const int checkOffset = ((safeDecode) && (dictSize < (int)(64 * KB)));
96 
97 	/* Set up the "end" pointers for the shortcut. */
98 	const BYTE *const shortiend = iend -
99 		(endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
100 	const BYTE *const shortoend = oend -
101 		(endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
102 
103 	DEBUGLOG(5, "%s (srcSize:%i, dstSize:%i)", __func__,
104 		 srcSize, outputSize);
105 
106 	/* Special cases */
107 	assert(lowPrefix <= op);
108 	assert(src != NULL);
109 
110 	/* Empty output buffer */
111 	if ((endOnInput) && (unlikely(outputSize == 0)))
112 		return ((srcSize == 1) && (*ip == 0)) ? 0 : -1;
113 
114 	if ((!endOnInput) && (unlikely(outputSize == 0)))
115 		return (*ip == 0 ? 1 : -1);
116 
117 	if ((endOnInput) && unlikely(srcSize == 0))
118 		return -1;
119 
120 	/* Main Loop : decode sequences */
121 	while (1) {
122 		size_t length;
123 		const BYTE *match;
124 		size_t offset;
125 
126 		/* get literal length */
127 		unsigned int const token = *ip++;
128 		length = token>>ML_BITS;
129 
130 		/* ip < iend before the increment */
131 		assert(!endOnInput || ip <= iend);
132 
133 		/*
134 		 * A two-stage shortcut for the most common case:
135 		 * 1) If the literal length is 0..14, and there is enough
136 		 * space, enter the shortcut and copy 16 bytes on behalf
137 		 * of the literals (in the fast mode, only 8 bytes can be
138 		 * safely copied this way).
139 		 * 2) Further if the match length is 4..18, copy 18 bytes
140 		 * in a similar manner; but we ensure that there's enough
141 		 * space in the output for those 18 bytes earlier, upon
142 		 * entering the shortcut (in other words, there is a
143 		 * combined check for both stages).
144 		 */
145 		if ((endOnInput ? length != RUN_MASK : length <= 8)
146 		   /*
147 		    * strictly "less than" on input, to re-enter
148 		    * the loop with at least one byte
149 		    */
150 		   && likely((endOnInput ? ip < shortiend : 1) &
151 			     (op <= shortoend))) {
152 			/* Copy the literals */
153 			memcpy(op, ip, endOnInput ? 16 : 8);
154 			op += length; ip += length;
155 
156 			/*
157 			 * The second stage:
158 			 * prepare for match copying, decode full info.
159 			 * If it doesn't work out, the info won't be wasted.
160 			 */
161 			length = token & ML_MASK; /* match length */
162 			offset = LZ4_readLE16(ip);
163 			ip += 2;
164 			match = op - offset;
165 			assert(match <= op); /* check overflow */
166 
167 			/* Do not deal with overlapping matches. */
168 			if ((length != ML_MASK) &&
169 			    (offset >= 8) &&
170 			    (dict == withPrefix64k || match >= lowPrefix)) {
171 				/* Copy the match. */
172 				memcpy(op + 0, match + 0, 8);
173 				memcpy(op + 8, match + 8, 8);
174 				memcpy(op + 16, match + 16, 2);
175 				op += length + MINMATCH;
176 				/* Both stages worked, load the next token. */
177 				continue;
178 			}
179 
180 			/*
181 			 * The second stage didn't work out, but the info
182 			 * is ready. Propel it right to the point of match
183 			 * copying.
184 			 */
185 			goto _copy_match;
186 		}
187 
188 		/* decode literal length */
189 		if (length == RUN_MASK) {
190 			unsigned int s;
191 
192 			if (unlikely(endOnInput ? ip >= iend - RUN_MASK : 0)) {
193 				/* overflow detection */
194 				goto _output_error;
195 			}
196 			do {
197 				s = *ip++;
198 				length += s;
199 			} while (likely(endOnInput
200 				? ip < iend - RUN_MASK
201 				: 1) & (s == 255));
202 
203 			if ((safeDecode)
204 			    && unlikely((uptrval)(op) +
205 					length < (uptrval)(op))) {
206 				/* overflow detection */
207 				goto _output_error;
208 			}
209 			if ((safeDecode)
210 			    && unlikely((uptrval)(ip) +
211 					length < (uptrval)(ip))) {
212 				/* overflow detection */
213 				goto _output_error;
214 			}
215 		}
216 
217 		/* copy literals */
218 		cpy = op + length;
219 		LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);
220 
221 		if (((endOnInput) && ((cpy > oend - MFLIMIT)
222 			|| (ip + length > iend - (2 + 1 + LASTLITERALS))))
223 			|| ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
224 			if (partialDecoding) {
225 				if (cpy > oend) {
226 					/*
227 					 * Partial decoding :
228 					 * stop in the middle of literal segment
229 					 */
230 					cpy = oend;
231 					length = oend - op;
232 				}
233 				if ((endOnInput)
234 					&& (ip + length > iend)) {
235 					/*
236 					 * Error :
237 					 * read attempt beyond
238 					 * end of input buffer
239 					 */
240 					goto _output_error;
241 				}
242 			} else {
243 				if ((!endOnInput)
244 					&& (cpy != oend)) {
245 					/*
246 					 * Error :
247 					 * block decoding must
248 					 * stop exactly there
249 					 */
250 					goto _output_error;
251 				}
252 				if ((endOnInput)
253 					&& ((ip + length != iend)
254 					|| (cpy > oend))) {
255 					/*
256 					 * Error :
257 					 * input must be consumed
258 					 */
259 					goto _output_error;
260 				}
261 			}
262 
263 			memcpy(op, ip, length);
264 			ip += length;
265 			op += length;
266 
267 			/* Necessarily EOF, due to parsing restrictions */
268 			if (!partialDecoding || (cpy == oend))
269 				break;
270 		} else {
271 			/* may overwrite up to WILDCOPYLENGTH beyond cpy */
272 			LZ4_wildCopy(op, ip, cpy);
273 			ip += length;
274 			op = cpy;
275 		}
276 
277 		/* get offset */
278 		offset = LZ4_readLE16(ip);
279 		ip += 2;
280 		match = op - offset;
281 
282 		/* get matchlength */
283 		length = token & ML_MASK;
284 
285 _copy_match:
286 		if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) {
287 			/* Error : offset outside buffers */
288 			goto _output_error;
289 		}
290 
291 		/* costs ~1%; silence an msan warning when offset == 0 */
292 		/*
293 		 * note : when partialDecoding, there is no guarantee that
294 		 * at least 4 bytes remain available in output buffer
295 		 */
296 		if (!partialDecoding) {
297 			assert(oend > op);
298 			assert(oend - op >= 4);
299 
300 			LZ4_write32(op, (U32)offset);
301 		}
302 
303 		if (length == ML_MASK) {
304 			unsigned int s;
305 
306 			do {
307 				s = *ip++;
308 
309 				if ((endOnInput) && (ip > iend - LASTLITERALS))
310 					goto _output_error;
311 
312 				length += s;
313 			} while (s == 255);
314 
315 			if ((safeDecode)
316 				&& unlikely(
317 					(uptrval)(op) + length < (uptrval)op)) {
318 				/* overflow detection */
319 				goto _output_error;
320 			}
321 		}
322 
323 		length += MINMATCH;
324 
325 		/* match starting within external dictionary */
326 		if ((dict == usingExtDict) && (match < lowPrefix)) {
327 			if (unlikely(op + length > oend - LASTLITERALS)) {
328 				/* doesn't respect parsing restriction */
329 				if (!partialDecoding)
330 					goto _output_error;
331 				length = min(length, (size_t)(oend - op));
332 			}
333 
334 			if (length <= (size_t)(lowPrefix - match)) {
335 				/*
336 				 * match fits entirely within external
337 				 * dictionary : just copy
338 				 */
339 				memmove(op, dictEnd - (lowPrefix - match),
340 					length);
341 				op += length;
342 			} else {
343 				/*
344 				 * match stretches into both external
345 				 * dictionary and current block
346 				 */
347 				size_t const copySize = (size_t)(lowPrefix - match);
348 				size_t const restSize = length - copySize;
349 
350 				memcpy(op, dictEnd - copySize, copySize);
351 				op += copySize;
352 				if (restSize > (size_t)(op - lowPrefix)) {
353 					/* overlap copy */
354 					BYTE * const endOfMatch = op + restSize;
355 					const BYTE *copyFrom = lowPrefix;
356 
357 					while (op < endOfMatch)
358 						*op++ = *copyFrom++;
359 				} else {
360 					memcpy(op, lowPrefix, restSize);
361 					op += restSize;
362 				}
363 			}
364 			continue;
365 		}
366 
367 		/* copy match within block */
368 		cpy = op + length;
369 
370 		/*
371 		 * partialDecoding :
372 		 * may not respect endBlock parsing restrictions
373 		 */
374 		assert(op <= oend);
375 		if (partialDecoding &&
376 		    (cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
377 			size_t const mlen = min(length, (size_t)(oend - op));
378 			const BYTE * const matchEnd = match + mlen;
379 			BYTE * const copyEnd = op + mlen;
380 
381 			if (matchEnd > op) {
382 				/* overlap copy */
383 				while (op < copyEnd)
384 					*op++ = *match++;
385 			} else {
386 				memcpy(op, match, mlen);
387 			}
388 			op = copyEnd;
389 			if (op == oend)
390 				break;
391 			continue;
392 		}
393 
394 		if (unlikely(offset < 8)) {
395 			op[0] = match[0];
396 			op[1] = match[1];
397 			op[2] = match[2];
398 			op[3] = match[3];
399 			match += inc32table[offset];
400 			memcpy(op + 4, match, 4);
401 			match -= dec64table[offset];
402 		} else {
403 			LZ4_copy8(op, match);
404 			match += 8;
405 		}
406 
407 		op += 8;
408 
409 		if (unlikely(cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
410 			BYTE * const oCopyLimit = oend - (WILDCOPYLENGTH - 1);
411 
412 			if (cpy > oend - LASTLITERALS) {
413 				/*
414 				 * Error : last LASTLITERALS bytes
415 				 * must be literals (uncompressed)
416 				 */
417 				goto _output_error;
418 			}
419 
420 			if (op < oCopyLimit) {
421 				LZ4_wildCopy(op, match, oCopyLimit);
422 				match += oCopyLimit - op;
423 				op = oCopyLimit;
424 			}
425 			while (op < cpy)
426 				*op++ = *match++;
427 		} else {
428 			LZ4_copy8(op, match);
429 			if (length > 16)
430 				LZ4_wildCopy(op + 8, match + 8, cpy);
431 		}
432 		op = cpy; /* wildcopy correction */
433 	}
434 
435 	/* end of decoding */
436 	if (endOnInput) {
437 		/* Nb of output bytes decoded */
438 		return (int) (((char *)op) - dst);
439 	} else {
440 		/* Nb of input bytes read */
441 		return (int) (((const char *)ip) - src);
442 	}
443 
444 	/* Overflow error detected */
445 _output_error:
446 	return (int) (-(((const char *)ip) - src)) - 1;
447 }
448 
449 int LZ4_decompress_safe(const char *source, char *dest,
450 	int compressedSize, int maxDecompressedSize)
451 {
452 	return LZ4_decompress_generic(source, dest,
453 				      compressedSize, maxDecompressedSize,
454 				      endOnInputSize, decode_full_block,
455 				      noDict, (BYTE *)dest, NULL, 0);
456 }
457 
458 int LZ4_decompress_safe_partial(const char *src, char *dst,
459 	int compressedSize, int targetOutputSize, int dstCapacity)
460 {
461 	dstCapacity = min(targetOutputSize, dstCapacity);
462 	return LZ4_decompress_generic(src, dst, compressedSize, dstCapacity,
463 				      endOnInputSize, partial_decode,
464 				      noDict, (BYTE *)dst, NULL, 0);
465 }
466 
467 int LZ4_decompress_fast(const char *source, char *dest, int originalSize)
468 {
469 	return LZ4_decompress_generic(source, dest, 0, originalSize,
470 				      endOnOutputSize, decode_full_block,
471 				      withPrefix64k,
472 				      (BYTE *)dest - 64 * KB, NULL, 0);
473 }
474 
475 /* ===== Instantiate a few more decoding cases, used more than once. ===== */
476 
477 int LZ4_decompress_safe_withPrefix64k(const char *source, char *dest,
478 				      int compressedSize, int maxOutputSize)
479 {
480 	return LZ4_decompress_generic(source, dest,
481 				      compressedSize, maxOutputSize,
482 				      endOnInputSize, decode_full_block,
483 				      withPrefix64k,
484 				      (BYTE *)dest - 64 * KB, NULL, 0);
485 }
486 
487 static int LZ4_decompress_safe_withSmallPrefix(const char *source, char *dest,
488 					       int compressedSize,
489 					       int maxOutputSize,
490 					       size_t prefixSize)
491 {
492 	return LZ4_decompress_generic(source, dest,
493 				      compressedSize, maxOutputSize,
494 				      endOnInputSize, decode_full_block,
495 				      noDict,
496 				      (BYTE *)dest - prefixSize, NULL, 0);
497 }
498 
499 int LZ4_decompress_safe_forceExtDict(const char *source, char *dest,
500 				     int compressedSize, int maxOutputSize,
501 				     const void *dictStart, size_t dictSize)
502 {
503 	return LZ4_decompress_generic(source, dest,
504 				      compressedSize, maxOutputSize,
505 				      endOnInputSize, decode_full_block,
506 				      usingExtDict, (BYTE *)dest,
507 				      (const BYTE *)dictStart, dictSize);
508 }
509 
510 static int LZ4_decompress_fast_extDict(const char *source, char *dest,
511 				       int originalSize,
512 				       const void *dictStart, size_t dictSize)
513 {
514 	return LZ4_decompress_generic(source, dest,
515 				      0, originalSize,
516 				      endOnOutputSize, decode_full_block,
517 				      usingExtDict, (BYTE *)dest,
518 				      (const BYTE *)dictStart, dictSize);
519 }
520 
521 /*
522  * The "double dictionary" mode, for use with e.g. ring buffers: the first part
523  * of the dictionary is passed as prefix, and the second via dictStart + dictSize.
524  * These routines are used only once, in LZ4_decompress_*_continue().
525  */
526 static FORCE_INLINE
527 int LZ4_decompress_safe_doubleDict(const char *source, char *dest,
528 				   int compressedSize, int maxOutputSize,
529 				   size_t prefixSize,
530 				   const void *dictStart, size_t dictSize)
531 {
532 	return LZ4_decompress_generic(source, dest,
533 				      compressedSize, maxOutputSize,
534 				      endOnInputSize, decode_full_block,
535 				      usingExtDict, (BYTE *)dest - prefixSize,
536 				      (const BYTE *)dictStart, dictSize);
537 }
538 
539 static FORCE_INLINE
540 int LZ4_decompress_fast_doubleDict(const char *source, char *dest,
541 				   int originalSize, size_t prefixSize,
542 				   const void *dictStart, size_t dictSize)
543 {
544 	return LZ4_decompress_generic(source, dest,
545 				      0, originalSize,
546 				      endOnOutputSize, decode_full_block,
547 				      usingExtDict, (BYTE *)dest - prefixSize,
548 				      (const BYTE *)dictStart, dictSize);
549 }
550 
551 /* ===== streaming decompression functions ===== */
552 
553 int LZ4_setStreamDecode(LZ4_streamDecode_t *LZ4_streamDecode,
554 	const char *dictionary, int dictSize)
555 {
556 	LZ4_streamDecode_t_internal *lz4sd =
557 		&LZ4_streamDecode->internal_donotuse;
558 
559 	lz4sd->prefixSize = (size_t) dictSize;
560 	lz4sd->prefixEnd = (const BYTE *) dictionary + dictSize;
561 	lz4sd->externalDict = NULL;
562 	lz4sd->extDictSize	= 0;
563 	return 1;
564 }
565 
566 /*
567  * *_continue() :
568  * These decoding functions allow decompression of multiple blocks
569  * in "streaming" mode.
570  * Previously decoded blocks must still be available at the memory
571  * position where they were decoded.
572  * If it's not possible, save the relevant part of
573  * decoded data into a safe buffer,
574  * and indicate where it stands using LZ4_setStreamDecode()
575  */
576 int LZ4_decompress_safe_continue(LZ4_streamDecode_t *LZ4_streamDecode,
577 	const char *source, char *dest, int compressedSize, int maxOutputSize)
578 {
579 	LZ4_streamDecode_t_internal *lz4sd =
580 		&LZ4_streamDecode->internal_donotuse;
581 	int result;
582 
583 	if (lz4sd->prefixSize == 0) {
584 		/* The first call, no dictionary yet. */
585 		assert(lz4sd->extDictSize == 0);
586 		result = LZ4_decompress_safe(source, dest,
587 			compressedSize, maxOutputSize);
588 		if (result <= 0)
589 			return result;
590 		lz4sd->prefixSize = result;
591 		lz4sd->prefixEnd = (BYTE *)dest + result;
592 	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
593 		/* They're rolling the current segment. */
594 		if (lz4sd->prefixSize >= 64 * KB - 1)
595 			result = LZ4_decompress_safe_withPrefix64k(source, dest,
596 				compressedSize, maxOutputSize);
597 		else if (lz4sd->extDictSize == 0)
598 			result = LZ4_decompress_safe_withSmallPrefix(source,
599 				dest, compressedSize, maxOutputSize,
600 				lz4sd->prefixSize);
601 		else
602 			result = LZ4_decompress_safe_doubleDict(source, dest,
603 				compressedSize, maxOutputSize,
604 				lz4sd->prefixSize,
605 				lz4sd->externalDict, lz4sd->extDictSize);
606 		if (result <= 0)
607 			return result;
608 		lz4sd->prefixSize += result;
609 		lz4sd->prefixEnd  += result;
610 	} else {
611 		/*
612 		 * The buffer wraps around, or they're
613 		 * switching to another buffer.
614 		 */
615 		lz4sd->extDictSize = lz4sd->prefixSize;
616 		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
617 		result = LZ4_decompress_safe_forceExtDict(source, dest,
618 			compressedSize, maxOutputSize,
619 			lz4sd->externalDict, lz4sd->extDictSize);
620 		if (result <= 0)
621 			return result;
622 		lz4sd->prefixSize = result;
623 		lz4sd->prefixEnd  = (BYTE *)dest + result;
624 	}
625 
626 	return result;
627 }
628 
629 int LZ4_decompress_fast_continue(LZ4_streamDecode_t *LZ4_streamDecode,
630 	const char *source, char *dest, int originalSize)
631 {
632 	LZ4_streamDecode_t_internal *lz4sd = &LZ4_streamDecode->internal_donotuse;
633 	int result;
634 
635 	if (lz4sd->prefixSize == 0) {
636 		assert(lz4sd->extDictSize == 0);
637 		result = LZ4_decompress_fast(source, dest, originalSize);
638 		if (result <= 0)
639 			return result;
640 		lz4sd->prefixSize = originalSize;
641 		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
642 	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
643 		if (lz4sd->prefixSize >= 64 * KB - 1 ||
644 		    lz4sd->extDictSize == 0)
645 			result = LZ4_decompress_fast(source, dest,
646 						     originalSize);
647 		else
648 			result = LZ4_decompress_fast_doubleDict(source, dest,
649 				originalSize, lz4sd->prefixSize,
650 				lz4sd->externalDict, lz4sd->extDictSize);
651 		if (result <= 0)
652 			return result;
653 		lz4sd->prefixSize += originalSize;
654 		lz4sd->prefixEnd  += originalSize;
655 	} else {
656 		lz4sd->extDictSize = lz4sd->prefixSize;
657 		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
658 		result = LZ4_decompress_fast_extDict(source, dest,
659 			originalSize, lz4sd->externalDict, lz4sd->extDictSize);
660 		if (result <= 0)
661 			return result;
662 		lz4sd->prefixSize = originalSize;
663 		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
664 	}
665 	return result;
666 }
667 
668 int LZ4_decompress_safe_usingDict(const char *source, char *dest,
669 				  int compressedSize, int maxOutputSize,
670 				  const char *dictStart, int dictSize)
671 {
672 	if (dictSize == 0)
673 		return LZ4_decompress_safe(source, dest,
674 					   compressedSize, maxOutputSize);
675 	if (dictStart+dictSize == dest) {
676 		if (dictSize >= 64 * KB - 1)
677 			return LZ4_decompress_safe_withPrefix64k(source, dest,
678 				compressedSize, maxOutputSize);
679 		return LZ4_decompress_safe_withSmallPrefix(source, dest,
680 			compressedSize, maxOutputSize, dictSize);
681 	}
682 	return LZ4_decompress_safe_forceExtDict(source, dest,
683 		compressedSize, maxOutputSize, dictStart, dictSize);
684 }
685 
686 int LZ4_decompress_fast_usingDict(const char *source, char *dest,
687 				  int originalSize,
688 				  const char *dictStart, int dictSize)
689 {
690 	if (dictSize == 0 || dictStart + dictSize == dest)
691 		return LZ4_decompress_fast(source, dest, originalSize);
692 
693 	return LZ4_decompress_fast_extDict(source, dest, originalSize,
694 		dictStart, dictSize);
695 }
696 
697 #ifndef STATIC
698 EXPORT_SYMBOL(LZ4_decompress_safe);
699 EXPORT_SYMBOL(LZ4_decompress_safe_partial);
700 EXPORT_SYMBOL(LZ4_decompress_fast);
701 EXPORT_SYMBOL(LZ4_setStreamDecode);
702 EXPORT_SYMBOL(LZ4_decompress_safe_continue);
703 EXPORT_SYMBOL(LZ4_decompress_fast_continue);
704 EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
705 EXPORT_SYMBOL(LZ4_decompress_fast_usingDict);
706 
707 MODULE_LICENSE("Dual BSD/GPL");
708 MODULE_DESCRIPTION("LZ4 decompressor");
709 #endif
710