xref: /linux-6.12.1/lib/lz4/lz4_decompress.c

/*
 * LZ4 - Fast LZ compression algorithm
 * Copyright (C) 2011 - 2016, Yann Collet.
 * BSD 2 - Clause License (http://www.opensource.org/licenses/bsd - license.php)
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *	* Redistributions of source code must retain the above copyright
 *	  notice, this list of conditions and the following disclaimer.
 *	* Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * You can contact the author at :
 *	- LZ4 homepage : http://www.lz4.org
 *	- LZ4 source repository : https://github.com/lz4/lz4
 *
 *	Changed for kernel usage by:
 *	Sven Schmidt <4sschmid@informatik.uni-hamburg.de>
 */

/*-************************************
 *	Dependencies
 **************************************/
#include <linux/lz4.h>
#include "lz4defs.h"
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/unaligned.h>

/*-*****************************
 *	Decompression functions
 *******************************/

#define DEBUGLOG(l, ...) {}	/* disabled */

#ifndef assert
#define assert(condition) ((void)0)
#endif

/*
 * LZ4_decompress_generic() :
 * This generic decompression function covers all use cases.
 * It shall be instantiated several times, using different sets of directives.
 * Note that it is important for performance that this function really get inlined,
 * in order to remove useless branches during compilation optimization.
 */
static FORCE_INLINE int LZ4_decompress_generic(
	 const char * const src,
	 char * const dst,
	 int srcSize,
		/*
		 * If endOnInput == endOnInputSize,
		 * this value is `dstCapacity`
		 */
	 int outputSize,
	 /* endOnOutputSize, endOnInputSize */
	 endCondition_directive endOnInput,
	 /* full, partial */
	 earlyEnd_directive partialDecoding,
	 /* noDict, withPrefix64k, usingExtDict */
	 dict_directive dict,
	 /* always <= dst, == dst when no prefix */
	 const BYTE * const lowPrefix,
	 /* only if dict == usingExtDict */
	 const BYTE * const dictStart,
	 /* note : = 0 if noDict */
	 const size_t dictSize
	 )
{
	const BYTE *ip = (const BYTE *) src;
	const BYTE * const iend = ip + srcSize;

	BYTE *op = (BYTE *) dst;
	BYTE * const oend = op + outputSize;
	BYTE *cpy;

	const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
	static const unsigned int inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
	static const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};

	const int safeDecode = (endOnInput == endOnInputSize);
	const int checkOffset = ((safeDecode) && (dictSize < (int)(64 * KB)));

	/* Set up the "end" pointers for the shortcut. */
	const BYTE *const shortiend = iend -
		(endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
	const BYTE *const shortoend = oend -
		(endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;

	DEBUGLOG(5, "%s (srcSize:%i, dstSize:%i)", __func__,
		 srcSize, outputSize);

	/* Special cases */
	assert(lowPrefix <= op);
	assert(src != NULL);

	/* Empty output buffer */
	if ((endOnInput) && (unlikely(outputSize == 0)))
		return ((srcSize == 1) && (*ip == 0)) ? 0 : -1;

	if ((!endOnInput) && (unlikely(outputSize == 0)))
		return (*ip == 0 ? 1 : -1);

	if ((endOnInput) && unlikely(srcSize == 0))
		return -1;

	/* Main Loop : decode sequences */
	while (1) {
		size_t length;
		const BYTE *match;
		size_t offset;

		/* get literal length */
		unsigned int const token = *ip++;
		length = token>>ML_BITS;

		/* ip < iend before the increment */
		assert(!endOnInput || ip <= iend);

		/*
		 * A two-stage shortcut for the most common case:
		 * 1) If the literal length is 0..14, and there is enough
		 * space, enter the shortcut and copy 16 bytes on behalf
		 * of the literals (in the fast mode, only 8 bytes can be
		 * safely copied this way).
		 * 2) Further if the match length is 4..18, copy 18 bytes
		 * in a similar manner; but we ensure that there's enough
		 * space in the output for those 18 bytes earlier, upon
		 * entering the shortcut (in other words, there is a
		 * combined check for both stages).
		 *
		 * The & in the likely() below is intentionally not && so that
		 * some compilers can produce better parallelized runtime code
		 */
		if ((endOnInput ? length != RUN_MASK : length <= 8)
		   /*
		    * strictly "less than" on input, to re-enter
		    * the loop with at least one byte
		    */
		   && likely((endOnInput ? ip < shortiend : 1) &
			     (op <= shortoend))) {
			/* Copy the literals */
			LZ4_memcpy(op, ip, endOnInput ? 16 : 8);
			op += length; ip += length;

			/*
			 * The second stage:
			 * prepare for match copying, decode full info.
			 * If it doesn't work out, the info won't be wasted.
			 */
			length = token & ML_MASK; /* match length */
			offset = LZ4_readLE16(ip);
			ip += 2;
			match = op - offset;
			assert(match <= op); /* check overflow */

			/* Do not deal with overlapping matches. */
			if ((length != ML_MASK) &&
			    (offset >= 8) &&
			    (dict == withPrefix64k || match >= lowPrefix)) {
				/* Copy the match. */
				LZ4_memcpy(op + 0, match + 0, 8);
				LZ4_memcpy(op + 8, match + 8, 8);
				LZ4_memcpy(op + 16, match + 16, 2);
				op += length + MINMATCH;
				/* Both stages worked, load the next token. */
				continue;
			}

			/*
			 * The second stage didn't work out, but the info
			 * is ready. Propel it right to the point of match
			 * copying.
			 */
			goto _copy_match;
		}

		/* decode literal length */
		if (length == RUN_MASK) {
			unsigned int s;

			if (unlikely(endOnInput ? ip >= iend - RUN_MASK : 0)) {
				/* overflow detection */
				goto _output_error;
			}
			do {
				s = *ip++;
				length += s;
			} while (likely(endOnInput
				? ip < iend - RUN_MASK
				: 1) & (s == 255));

			if ((safeDecode)
			    && unlikely((uptrval)(op) +
					length < (uptrval)(op))) {
				/* overflow detection */
				goto _output_error;
			}
			if ((safeDecode)
			    && unlikely((uptrval)(ip) +
					length < (uptrval)(ip))) {
				/* overflow detection */
				goto _output_error;
			}
		}

		/* copy literals */
		cpy = op + length;
		LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);

		if (((endOnInput) && ((cpy > oend - MFLIMIT)
			|| (ip + length > iend - (2 + 1 + LASTLITERALS))))
			|| ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
			if (partialDecoding) {
				if (cpy > oend) {
					/*
					 * Partial decoding :
					 * stop in the middle of literal segment
					 */
					cpy = oend;
					length = oend - op;
				}
				if ((endOnInput)
					&& (ip + length > iend)) {
					/*
					 * Error :
					 * read attempt beyond
					 * end of input buffer
					 */
					goto _output_error;
				}
			} else {
				if ((!endOnInput)
					&& (cpy != oend)) {
					/*
					 * Error :
					 * block decoding must
					 * stop exactly there
					 */
					goto _output_error;
				}
				if ((endOnInput)
					&& ((ip + length != iend)
					|| (cpy > oend))) {
					/*
					 * Error :
					 * input must be consumed
					 */
					goto _output_error;
				}
			}

			/*
			 * supports overlapping memory regions; only matters
			 * for in-place decompression scenarios
			 */
			LZ4_memmove(op, ip, length);
			ip += length;
			op += length;

			/* Necessarily EOF when !partialDecoding.
			 * When partialDecoding, it is EOF if we've either
			 * filled the output buffer or
			 * can't proceed with reading an offset for following match.
			 */
			if (!partialDecoding || (cpy == oend) || (ip >= (iend - 2)))
				break;
		} else {
			/* may overwrite up to WILDCOPYLENGTH beyond cpy */
			LZ4_wildCopy(op, ip, cpy);
			ip += length;
			op = cpy;
		}

		/* get offset */
		offset = LZ4_readLE16(ip);
		ip += 2;
		match = op - offset;

		/* get matchlength */
		length = token & ML_MASK;

_copy_match:
		if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) {
			/* Error : offset outside buffers */
			goto _output_error;
		}

		/* costs ~1%; silence an msan warning when offset == 0 */
		/*
		 * note : when partialDecoding, there is no guarantee that
		 * at least 4 bytes remain available in output buffer
		 */
		if (!partialDecoding) {
			assert(oend > op);
			assert(oend - op >= 4);

			LZ4_write32(op, (U32)offset);
		}

		if (length == ML_MASK) {
			unsigned int s;

			do {
				s = *ip++;

				if ((endOnInput) && (ip > iend - LASTLITERALS))
					goto _output_error;

				length += s;
			} while (s == 255);

			if ((safeDecode)
				&& unlikely(
					(uptrval)(op) + length < (uptrval)op)) {
				/* overflow detection */
				goto _output_error;
			}
		}

		length += MINMATCH;

		/* match starting within external dictionary */
		if ((dict == usingExtDict) && (match < lowPrefix)) {
			if (unlikely(op + length > oend - LASTLITERALS)) {
				/* doesn't respect parsing restriction */
				if (!partialDecoding)
					goto _output_error;
				length = min(length, (size_t)(oend - op));
			}

			if (length <= (size_t)(lowPrefix - match)) {
				/*
				 * match fits entirely within external
				 * dictionary : just copy
				 */
				memmove(op, dictEnd - (lowPrefix - match),
					length);
				op += length;
			} else {
				/*
				 * match stretches into both external
				 * dictionary and current block
				 */
				size_t const copySize = (size_t)(lowPrefix - match);
				size_t const restSize = length - copySize;

				LZ4_memcpy(op, dictEnd - copySize, copySize);
				op += copySize;
				if (restSize > (size_t)(op - lowPrefix)) {
					/* overlap copy */
					BYTE * const endOfMatch = op + restSize;
					const BYTE *copyFrom = lowPrefix;

					while (op < endOfMatch)
						*op++ = *copyFrom++;
				} else {
					LZ4_memcpy(op, lowPrefix, restSize);
					op += restSize;
				}
			}
			continue;
		}

		/* copy match within block */
		cpy = op + length;

		/*
		 * partialDecoding :
		 * may not respect endBlock parsing restrictions
		 */
		assert(op <= oend);
		if (partialDecoding &&
		    (cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
			size_t const mlen = min(length, (size_t)(oend - op));
			const BYTE * const matchEnd = match + mlen;
			BYTE * const copyEnd = op + mlen;

			if (matchEnd > op) {
				/* overlap copy */
				while (op < copyEnd)
					*op++ = *match++;
			} else {
				LZ4_memcpy(op, match, mlen);
			}
			op = copyEnd;
			if (op == oend)
				break;
			continue;
		}

		if (unlikely(offset < 8)) {
			op[0] = match[0];
			op[1] = match[1];
			op[2] = match[2];
			op[3] = match[3];
			match += inc32table[offset];
			LZ4_memcpy(op + 4, match, 4);
			match -= dec64table[offset];
		} else {
			LZ4_copy8(op, match);
			match += 8;
		}

		op += 8;

		if (unlikely(cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
			BYTE * const oCopyLimit = oend - (WILDCOPYLENGTH - 1);

			if (cpy > oend - LASTLITERALS) {
				/*
				 * Error : last LASTLITERALS bytes
				 * must be literals (uncompressed)
				 */
				goto _output_error;
			}

			if (op < oCopyLimit) {
				LZ4_wildCopy(op, match, oCopyLimit);
				match += oCopyLimit - op;
				op = oCopyLimit;
			}
			while (op < cpy)
				*op++ = *match++;
		} else {
			LZ4_copy8(op, match);
			if (length > 16)
				LZ4_wildCopy(op + 8, match + 8, cpy);
		}
		op = cpy; /* wildcopy correction */
	}

	/* end of decoding */
	if (endOnInput) {
		/* Nb of output bytes decoded */
		return (int) (((char *)op) - dst);
	} else {
		/* Nb of input bytes read */
		return (int) (((const char *)ip) - src);
	}

	/* Overflow error detected */
_output_error:
	return (int) (-(((const char *)ip) - src)) - 1;
}

int LZ4_decompress_safe(const char *source, char *dest,
	int compressedSize, int maxDecompressedSize)
{
	return LZ4_decompress_generic(source, dest,
				      compressedSize, maxDecompressedSize,
				      endOnInputSize, decode_full_block,
				      noDict, (BYTE *)dest, NULL, 0);
}

int LZ4_decompress_safe_partial(const char *src, char *dst,
	int compressedSize, int targetOutputSize, int dstCapacity)
{
	dstCapacity = min(targetOutputSize, dstCapacity);
	return LZ4_decompress_generic(src, dst, compressedSize, dstCapacity,
				      endOnInputSize, partial_decode,
				      noDict, (BYTE *)dst, NULL, 0);
}

int LZ4_decompress_fast(const char *source, char *dest, int originalSize)
{
	return LZ4_decompress_generic(source, dest, 0, originalSize,
				      endOnOutputSize, decode_full_block,
				      withPrefix64k,
				      (BYTE *)dest - 64 * KB, NULL, 0);
}

/* ===== Instantiate a few more decoding cases, used more than once. ===== */

static int LZ4_decompress_safe_withPrefix64k(const char *source, char *dest,
				      int compressedSize, int maxOutputSize)
{
	return LZ4_decompress_generic(source, dest,
				      compressedSize, maxOutputSize,
				      endOnInputSize, decode_full_block,
				      withPrefix64k,
				      (BYTE *)dest - 64 * KB, NULL, 0);
}

static int LZ4_decompress_safe_withSmallPrefix(const char *source, char *dest,
					       int compressedSize,
					       int maxOutputSize,
					       size_t prefixSize)
{
	return LZ4_decompress_generic(source, dest,
				      compressedSize, maxOutputSize,
				      endOnInputSize, decode_full_block,
				      noDict,
				      (BYTE *)dest - prefixSize, NULL, 0);
}

static int LZ4_decompress_safe_forceExtDict(const char *source, char *dest,
					    int compressedSize, int maxOutputSize,
					    const void *dictStart, size_t dictSize)
{
	return LZ4_decompress_generic(source, dest,
				      compressedSize, maxOutputSize,
				      endOnInputSize, decode_full_block,
				      usingExtDict, (BYTE *)dest,
				      (const BYTE *)dictStart, dictSize);
}

static int LZ4_decompress_fast_extDict(const char *source, char *dest,
				       int originalSize,
				       const void *dictStart, size_t dictSize)
{
	return LZ4_decompress_generic(source, dest,
				      0, originalSize,
				      endOnOutputSize, decode_full_block,
				      usingExtDict, (BYTE *)dest,
				      (const BYTE *)dictStart, dictSize);
}

/*
 * The "double dictionary" mode, for use with e.g. ring buffers: the first part
 * of the dictionary is passed as prefix, and the second via dictStart + dictSize.
 * These routines are used only once, in LZ4_decompress_*_continue().
 */
static FORCE_INLINE
int LZ4_decompress_safe_doubleDict(const char *source, char *dest,
				   int compressedSize, int maxOutputSize,
				   size_t prefixSize,
				   const void *dictStart, size_t dictSize)
{
	return LZ4_decompress_generic(source, dest,
				      compressedSize, maxOutputSize,
				      endOnInputSize, decode_full_block,
				      usingExtDict, (BYTE *)dest - prefixSize,
				      (const BYTE *)dictStart, dictSize);
}

static FORCE_INLINE
int LZ4_decompress_fast_doubleDict(const char *source, char *dest,
				   int originalSize, size_t prefixSize,
				   const void *dictStart, size_t dictSize)
{
	return LZ4_decompress_generic(source, dest,
				      0, originalSize,
				      endOnOutputSize, decode_full_block,
				      usingExtDict, (BYTE *)dest - prefixSize,
				      (const BYTE *)dictStart, dictSize);
}

/* ===== streaming decompression functions ===== */

int LZ4_setStreamDecode(LZ4_streamDecode_t *LZ4_streamDecode,
	const char *dictionary, int dictSize)
{
	LZ4_streamDecode_t_internal *lz4sd =
		&LZ4_streamDecode->internal_donotuse;

	lz4sd->prefixSize = (size_t) dictSize;
	lz4sd->prefixEnd = (const BYTE *) dictionary + dictSize;
	lz4sd->externalDict = NULL;
	lz4sd->extDictSize	= 0;
	return 1;
}

/*
 * *_continue() :
 * These decoding functions allow decompression of multiple blocks
 * in "streaming" mode.
 * Previously decoded blocks must still be available at the memory
 * position where they were decoded.
 * If it's not possible, save the relevant part of
 * decoded data into a safe buffer,
 * and indicate where it stands using LZ4_setStreamDecode()
 */
int LZ4_decompress_safe_continue(LZ4_streamDecode_t *LZ4_streamDecode,
	const char *source, char *dest, int compressedSize, int maxOutputSize)
{
	LZ4_streamDecode_t_internal *lz4sd =
		&LZ4_streamDecode->internal_donotuse;
	int result;

	if (lz4sd->prefixSize == 0) {
		/* The first call, no dictionary yet. */
		assert(lz4sd->extDictSize == 0);
		result = LZ4_decompress_safe(source, dest,
			compressedSize, maxOutputSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize = result;
		lz4sd->prefixEnd = (BYTE *)dest + result;
	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
		/* They're rolling the current segment. */
		if (lz4sd->prefixSize >= 64 * KB - 1)
			result = LZ4_decompress_safe_withPrefix64k(source, dest,
				compressedSize, maxOutputSize);
		else if (lz4sd->extDictSize == 0)
			result = LZ4_decompress_safe_withSmallPrefix(source,
				dest, compressedSize, maxOutputSize,
				lz4sd->prefixSize);
		else
			result = LZ4_decompress_safe_doubleDict(source, dest,
				compressedSize, maxOutputSize,
				lz4sd->prefixSize,
				lz4sd->externalDict, lz4sd->extDictSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize += result;
		lz4sd->prefixEnd  += result;
	} else {
		/*
		 * The buffer wraps around, or they're
		 * switching to another buffer.
		 */
		lz4sd->extDictSize = lz4sd->prefixSize;
		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
		result = LZ4_decompress_safe_forceExtDict(source, dest,
			compressedSize, maxOutputSize,
			lz4sd->externalDict, lz4sd->extDictSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize = result;
		lz4sd->prefixEnd  = (BYTE *)dest + result;
	}

	return result;
}

int LZ4_decompress_fast_continue(LZ4_streamDecode_t *LZ4_streamDecode,
	const char *source, char *dest, int originalSize)
{
	LZ4_streamDecode_t_internal *lz4sd = &LZ4_streamDecode->internal_donotuse;
	int result;

	if (lz4sd->prefixSize == 0) {
		assert(lz4sd->extDictSize == 0);
		result = LZ4_decompress_fast(source, dest, originalSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize = originalSize;
		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
	} else if (lz4sd->prefixEnd == (BYTE *)dest) {
		if (lz4sd->prefixSize >= 64 * KB - 1 ||
		    lz4sd->extDictSize == 0)
			result = LZ4_decompress_fast(source, dest,
						     originalSize);
		else
			result = LZ4_decompress_fast_doubleDict(source, dest,
				originalSize, lz4sd->prefixSize,
				lz4sd->externalDict, lz4sd->extDictSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize += originalSize;
		lz4sd->prefixEnd  += originalSize;
	} else {
		lz4sd->extDictSize = lz4sd->prefixSize;
		lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
		result = LZ4_decompress_fast_extDict(source, dest,
			originalSize, lz4sd->externalDict, lz4sd->extDictSize);
		if (result <= 0)
			return result;
		lz4sd->prefixSize = originalSize;
		lz4sd->prefixEnd = (BYTE *)dest + originalSize;
	}
	return result;
}

int LZ4_decompress_safe_usingDict(const char *source, char *dest,
				  int compressedSize, int maxOutputSize,
				  const char *dictStart, int dictSize)
{
	if (dictSize == 0)
		return LZ4_decompress_safe(source, dest,
					   compressedSize, maxOutputSize);
	if (dictStart+dictSize == dest) {
		if (dictSize >= 64 * KB - 1)
			return LZ4_decompress_safe_withPrefix64k(source, dest,
				compressedSize, maxOutputSize);
		return LZ4_decompress_safe_withSmallPrefix(source, dest,
			compressedSize, maxOutputSize, dictSize);
	}
	return LZ4_decompress_safe_forceExtDict(source, dest,
		compressedSize, maxOutputSize, dictStart, dictSize);
}

int LZ4_decompress_fast_usingDict(const char *source, char *dest,
				  int originalSize,
				  const char *dictStart, int dictSize)
{
	if (dictSize == 0 || dictStart + dictSize == dest)
		return LZ4_decompress_fast(source, dest, originalSize);

	return LZ4_decompress_fast_extDict(source, dest, originalSize,
		dictStart, dictSize);
}

#ifndef STATIC
EXPORT_SYMBOL(LZ4_decompress_safe);
EXPORT_SYMBOL(LZ4_decompress_safe_partial);
EXPORT_SYMBOL(LZ4_decompress_fast);
EXPORT_SYMBOL(LZ4_setStreamDecode);
EXPORT_SYMBOL(LZ4_decompress_safe_continue);
EXPORT_SYMBOL(LZ4_decompress_fast_continue);
EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
EXPORT_SYMBOL(LZ4_decompress_fast_usingDict);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_DESCRIPTION("LZ4 decompressor");
#endif