fs/ntfs3/lznt.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  *
  * Copyright (C) 2019-2021 Paragon Software GmbH, All rights reserved.
  *
  */

 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/stddef.h>
 #include <linux/string.h>
 #include <linux/types.h>

 #include "debug.h"
 #include "ntfs_fs.h"

 // clang-format off
 /* Src buffer is zero. */
 #define LZNT_ERROR_ALL_ZEROS	1
 #define LZNT_CHUNK_SIZE		0x1000
 // clang-format on

 struct lznt_hash {
 	const u8 *p1;
 	const u8 *p2;
 };

 struct lznt {
 	const u8 *unc;
 	const u8 *unc_end;
 	const u8 *best_match;
 	size_t max_len;
 	bool std;

 	struct lznt_hash hash[LZNT_CHUNK_SIZE];
 };

 static inline size_t get_match_len(const u8 *ptr, const u8 *end, const u8 *prev,
 				   size_t max_len)
 {
 	size_t len = 0;

 	while (ptr + len < end && ptr[len] == prev[len] && ++len < max_len)
 		;
 	return len;
 }

 static size_t longest_match_std(const u8 *src, struct lznt *ctx)
 {
 	size_t hash_index;
 	size_t len1 = 0, len2 = 0;
 	const u8 **hash;

 	hash_index =
 		((40543U * ((((src[0] << 4) ^ src[1]) << 4) ^ src[2])) >> 4) &
 		(LZNT_CHUNK_SIZE - 1);

 	hash = &(ctx->hash[hash_index].p1);

 	if (hash[0] >= ctx->unc && hash[0] < src && hash[0][0] == src[0] &&
 	    hash[0][1] == src[1] && hash[0][2] == src[2]) {
 		len1 = 3;
 		if (ctx->max_len > 3)
 			len1 += get_match_len(src + 3, ctx->unc_end,
 					      hash[0] + 3, ctx->max_len - 3);
 	}

 	if (hash[1] >= ctx->unc && hash[1] < src && hash[1][0] == src[0] &&
 	    hash[1][1] == src[1] && hash[1][2] == src[2]) {
 		len2 = 3;
 		if (ctx->max_len > 3)
 			len2 += get_match_len(src + 3, ctx->unc_end,
 					      hash[1] + 3, ctx->max_len - 3);
 	}

 	/* Compare two matches and select the best one. */
 	if (len1 < len2) {
 		ctx->best_match = hash[1];
 		len1 = len2;
 	} else {
 		ctx->best_match = hash[0];
 	}

 	hash[1] = hash[0];
 	hash[0] = src;
 	return len1;
 }

 static size_t longest_match_best(const u8 *src, struct lznt *ctx)
 {
 	size_t max_len;
 	const u8 *ptr;

 	if (ctx->unc >= src || !ctx->max_len)
 		return 0;

 	max_len = 0;
 	for (ptr = ctx->unc; ptr < src; ++ptr) {
 		size_t len =
 			get_match_len(src, ctx->unc_end, ptr, ctx->max_len);
 		if (len >= max_len) {
 			max_len = len;
 			ctx->best_match = ptr;
 		}
 	}

 	return max_len >= 3 ? max_len : 0;
 }

 static const size_t s_max_len[] = {
 	0x1002, 0x802, 0x402, 0x202, 0x102, 0x82, 0x42, 0x22, 0x12,
 };

 static const size_t s_max_off[] = {
 	0x10, 0x20, 0x40, 0x80, 0x100, 0x200, 0x400, 0x800, 0x1000,
 };

 static inline u16 make_pair(size_t offset, size_t len, size_t index)
 {
 	return ((offset - 1) << (12 - index)) |
 	       ((len - 3) & (((1 << (12 - index)) - 1)));
 }

 static inline size_t parse_pair(u16 pair, size_t *offset, size_t index)
 {
 	*offset = 1 + (pair >> (12 - index));
 	return 3 + (pair & ((1 << (12 - index)) - 1));
 }

 /*
  * compress_chunk
  *
  * Return:
  * * 0	- Ok, @cmpr contains @cmpr_chunk_size bytes of compressed data.
  * * 1	- Input buffer is full zero.
  * * -2 - The compressed buffer is too small to hold the compressed data.
  */
 static inline int compress_chunk(size_t (*match)(const u8 *, struct lznt *),
 				 const u8 *unc, const u8 *unc_end, u8 *cmpr,
 				 u8 *cmpr_end, size_t *cmpr_chunk_size,
 				 struct lznt *ctx)
 {
 	size_t cnt = 0;
 	size_t idx = 0;
 	const u8 *up = unc;
 	u8 *cp = cmpr + 3;
 	u8 *cp2 = cmpr + 2;
 	u8 not_zero = 0;
 	/* Control byte of 8-bit values: ( 0 - means byte as is, 1 - short pair ). */
 	u8 ohdr = 0;
 	u8 *last;
 	u16 t16;

 	if (unc + LZNT_CHUNK_SIZE < unc_end)
 		unc_end = unc + LZNT_CHUNK_SIZE;

 	last = min(cmpr + LZNT_CHUNK_SIZE + sizeof(short), cmpr_end);

 	ctx->unc = unc;
 	ctx->unc_end = unc_end;
 	ctx->max_len = s_max_len[0];

 	while (up < unc_end) {
 		size_t max_len;

 		while (unc + s_max_off[idx] < up)
 			ctx->max_len = s_max_len[++idx];

 		/* Find match. */
 		max_len = up + 3 <= unc_end ? (*match)(up, ctx) : 0;

 		if (!max_len) {
 			if (cp >= last)
 				goto NotCompressed;
 			not_zero |= *cp++ = *up++;
 		} else if (cp + 1 >= last) {
 			goto NotCompressed;
 		} else {
 			t16 = make_pair(up - ctx->best_match, max_len, idx);
 			*cp++ = t16;
 			*cp++ = t16 >> 8;

 			ohdr |= 1 << cnt;
 			up += max_len;
 		}

 		cnt = (cnt + 1) & 7;
 		if (!cnt) {
 			*cp2 = ohdr;
 			ohdr = 0;
 			cp2 = cp;
 			cp += 1;
 		}
 	}

 	if (cp2 < last)
 		*cp2 = ohdr;
 	else
 		cp -= 1;

 	*cmpr_chunk_size = cp - cmpr;

 	t16 = (*cmpr_chunk_size - 3) | 0xB000;
 	cmpr[0] = t16;
 	cmpr[1] = t16 >> 8;

 	return not_zero ? 0 : LZNT_ERROR_ALL_ZEROS;

 NotCompressed:

 	if ((cmpr + LZNT_CHUNK_SIZE + sizeof(short)) > last)
 		return -2;

 	/*
 	 * Copy non cmpr data.
 	 * 0x3FFF == ((LZNT_CHUNK_SIZE + 2 - 3) | 0x3000)
 	 */
 	cmpr[0] = 0xff;
 	cmpr[1] = 0x3f;

 	memcpy(cmpr + sizeof(short), unc, LZNT_CHUNK_SIZE);
 	*cmpr_chunk_size = LZNT_CHUNK_SIZE + sizeof(short);

 	return 0;
 }

 static inline ssize_t decompress_chunk(u8 *unc, u8 *unc_end, const u8 *cmpr,
 				       const u8 *cmpr_end)
 {
 	u8 *up = unc;
 	u8 ch = *cmpr++;
 	size_t bit = 0;
 	size_t index = 0;
 	u16 pair;
 	size_t offset, length;

 	/* Do decompression until pointers are inside range. */
 	while (up < unc_end && cmpr < cmpr_end) {
 		/* Correct index */
 		while (unc + s_max_off[index] < up)
 			index += 1;

 		/* Check the current flag for zero. */
 		if (!(ch & (1 << bit))) {
 			/* Just copy byte. */
 			*up++ = *cmpr++;
 			goto next;
 		}

 		/* Check for boundary. */
 		if (cmpr + 1 >= cmpr_end)
 			return -EINVAL;

 		/* Read a short from little endian stream. */
 		pair = cmpr[1];
 		pair <<= 8;
 		pair |= cmpr[0];

 		cmpr += 2;

 		/* Translate packed information into offset and length. */
 		length = parse_pair(pair, &offset, index);

 		/* Check offset for boundary. */
 		if (unc + offset > up)
 			return -EINVAL;

 		/* Truncate the length if necessary. */
 		if (up + length >= unc_end)
 			length = unc_end - up;

 		/* Now we copy bytes. This is the heart of LZ algorithm. */
 		for (; length > 0; length--, up++)
 			*up = *(up - offset);

 next:
 		/* Advance flag bit value. */
 		bit = (bit + 1) & 7;

 		if (!bit) {
 			if (cmpr >= cmpr_end)
 				break;

 			ch = *cmpr++;
 		}
 	}

 	/* Return the size of uncompressed data. */
 	return up - unc;
 }

 /*
  * get_lznt_ctx
  * @level: 0 - Standard compression.
  *	   !0 - Best compression, requires a lot of cpu.
  */
 struct lznt *get_lznt_ctx(int level)
 {
 	struct lznt *r = kzalloc(level ? offsetof(struct lznt, hash) :
 					 sizeof(struct lznt),
 				 GFP_NOFS);

 	if (r)
 		r->std = !level;
 	return r;
 }

 /*
  * compress_lznt - Compresses @unc into @cmpr
  *
  * Return:
  * * +x - Ok, @cmpr contains 'final_compressed_size' bytes of compressed data.
  * * 0 - Input buffer is full zero.
  */
 size_t compress_lznt(const void *unc, size_t unc_size, void *cmpr,
 		     size_t cmpr_size, struct lznt *ctx)
 {
 	int err;
 	size_t (*match)(const u8 *src, struct lznt *ctx);
 	u8 *p = cmpr;
 	u8 *end = p + cmpr_size;
 	const u8 *unc_chunk = unc;
 	const u8 *unc_end = unc_chunk + unc_size;
 	bool is_zero = true;

 	if (ctx->std) {
 		match = &longest_match_std;
 		memset(ctx->hash, 0, sizeof(ctx->hash));
 	} else {
 		match = &longest_match_best;
 	}

 	/* Compression cycle. */
 	for (; unc_chunk < unc_end; unc_chunk += LZNT_CHUNK_SIZE) {
 		cmpr_size = 0;
 		err = compress_chunk(match, unc_chunk, unc_end, p, end,
 				     &cmpr_size, ctx);
 		if (err < 0)
 			return unc_size;

 		if (is_zero && err != LZNT_ERROR_ALL_ZEROS)
 			is_zero = false;

 		p += cmpr_size;
 	}

 	if (p <= end - 2)
 		p[0] = p[1] = 0;

 	return is_zero ? 0 : PtrOffset(cmpr, p);
 }

 /*
  * decompress_lznt - Decompress @cmpr into @unc.
  */
 ssize_t decompress_lznt(const void *cmpr, size_t cmpr_size, void *unc,
 			size_t unc_size)
 {
 	const u8 *cmpr_chunk = cmpr;
 	const u8 *cmpr_end = cmpr_chunk + cmpr_size;
 	u8 *unc_chunk = unc;
 	u8 *unc_end = unc_chunk + unc_size;
 	u16 chunk_hdr;

 	if (cmpr_size < sizeof(short))
 		return -EINVAL;

 	/* Read chunk header. */
 	chunk_hdr = cmpr_chunk[1];
 	chunk_hdr <<= 8;
 	chunk_hdr |= cmpr_chunk[0];

 	/* Loop through decompressing chunks. */
 	for (;;) {
 		size_t chunk_size_saved;
 		size_t unc_use;
 		size_t cmpr_use = 3 + (chunk_hdr & (LZNT_CHUNK_SIZE - 1));

 		/* Check that the chunk actually fits the supplied buffer. */
 		if (cmpr_chunk + cmpr_use > cmpr_end)
 			return -EINVAL;

 		/* First make sure the chunk contains compressed data. */
 		if (chunk_hdr & 0x8000) {
 			/* Decompress a chunk and return if we get an error. */
 			ssize_t err =
 				decompress_chunk(unc_chunk, unc_end,
 						 cmpr_chunk + sizeof(chunk_hdr),
 						 cmpr_chunk + cmpr_use);
 			if (err < 0)
 				return err;
 			unc_use = err;
 		} else {
 			/* This chunk does not contain compressed data. */
 			unc_use = unc_chunk + LZNT_CHUNK_SIZE > unc_end ?
 					  unc_end - unc_chunk :
 					  LZNT_CHUNK_SIZE;

 			if (cmpr_chunk + sizeof(chunk_hdr) + unc_use >
 			    cmpr_end) {
 				return -EINVAL;
 			}

 			memcpy(unc_chunk, cmpr_chunk + sizeof(chunk_hdr),
 			       unc_use);
 		}

 		/* Advance pointers. */
 		cmpr_chunk += cmpr_use;
 		unc_chunk += unc_use;

 		/* Check for the end of unc buffer. */
 		if (unc_chunk >= unc_end)
 			break;

 		/* Proceed the next chunk. */
 		if (cmpr_chunk > cmpr_end - 2)
 			break;

 		chunk_size_saved = LZNT_CHUNK_SIZE;

 		/* Read chunk header. */
 		chunk_hdr = cmpr_chunk[1];
 		chunk_hdr <<= 8;
 		chunk_hdr |= cmpr_chunk[0];

 		if (!chunk_hdr)
 			break;

 		/* Check the size of unc buffer. */
 		if (unc_use < chunk_size_saved) {
 			size_t t1 = chunk_size_saved - unc_use;
 			u8 *t2 = unc_chunk + t1;

 			/* 'Zero' memory. */
 			if (t2 >= unc_end)
 				break;

 			memset(unc_chunk, 0, t1);
 			unc_chunk = t2;
 		}
 	}

 	/* Check compression boundary. */
 	if (cmpr_chunk > cmpr_end)
 		return -EINVAL;

 	/*
 	 * The unc size is just a difference between current
 	 * pointer and original one.
 	 */
 	return PtrOffset(unc, unc_chunk);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	*
	* Copyright (C) 2019-2021 Paragon Software GmbH, All rights reserved.
	*
	*/

	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/stddef.h>
	#include <linux/string.h>
	#include <linux/types.h>

	#include "debug.h"
	#include "ntfs_fs.h"

	// clang-format off
	/* Src buffer is zero. */
	#define LZNT_ERROR_ALL_ZEROS 1
	#define LZNT_CHUNK_SIZE 0x1000
	// clang-format on

	struct lznt_hash {
	const u8 *p1;
	const u8 *p2;
	};

	struct lznt {
	const u8 *unc;
	const u8 *unc_end;
	const u8 *best_match;
	size_t max_len;
	bool std;

	struct lznt_hash hash[LZNT_CHUNK_SIZE];
	};

	static inline size_t get_match_len(const u8 ptr, const u8 end, const u8 *prev,
	size_t max_len)
	{
	size_t len = 0;

	while (ptr + len < end && ptr[len] == prev[len] && ++len < max_len)
	;
	return len;
	}

	static size_t longest_match_std(const u8 src, struct lznt ctx)
	{
	size_t hash_index;
	size_t len1 = 0, len2 = 0;
	const u8 **hash;

	hash_index =
	((40543U * ((((src[0] << 4) ^ src[1]) << 4) ^ src[2])) >> 4) &
	(LZNT_CHUNK_SIZE - 1);

	hash = &(ctx->hash[hash_index].p1);

	if (hash[0] >= ctx->unc && hash[0] < src && hash[0][0] == src[0] &&
	hash[0][1] == src[1] && hash[0][2] == src[2]) {
	len1 = 3;
	if (ctx->max_len > 3)
	len1 += get_match_len(src + 3, ctx->unc_end,
	hash[0] + 3, ctx->max_len - 3);
	}

	if (hash[1] >= ctx->unc && hash[1] < src && hash[1][0] == src[0] &&
	hash[1][1] == src[1] && hash[1][2] == src[2]) {
	len2 = 3;
	if (ctx->max_len > 3)
	len2 += get_match_len(src + 3, ctx->unc_end,
	hash[1] + 3, ctx->max_len - 3);
	}

	/* Compare two matches and select the best one. */
	if (len1 < len2) {
	ctx->best_match = hash[1];
	len1 = len2;
	} else {
	ctx->best_match = hash[0];
	}

	hash[1] = hash[0];
	hash[0] = src;
	return len1;
	}

	static size_t longest_match_best(const u8 src, struct lznt ctx)
	{
	size_t max_len;
	const u8 *ptr;

	if (ctx->unc >= src \|\| !ctx->max_len)
	return 0;

	max_len = 0;
	for (ptr = ctx->unc; ptr < src; ++ptr) {
	size_t len =
	get_match_len(src, ctx->unc_end, ptr, ctx->max_len);
	if (len >= max_len) {
	max_len = len;
	ctx->best_match = ptr;
	}
	}

	return max_len >= 3 ? max_len : 0;
	}

	static const size_t s_max_len[] = {
	0x1002, 0x802, 0x402, 0x202, 0x102, 0x82, 0x42, 0x22, 0x12,
	};

	static const size_t s_max_off[] = {
	0x10, 0x20, 0x40, 0x80, 0x100, 0x200, 0x400, 0x800, 0x1000,
	};

	static inline u16 make_pair(size_t offset, size_t len, size_t index)
	{
	return ((offset - 1) << (12 - index)) \|
	((len - 3) & (((1 << (12 - index)) - 1)));
	}

	static inline size_t parse_pair(u16 pair, size_t *offset, size_t index)
	{
	*offset = 1 + (pair >> (12 - index));
	return 3 + (pair & ((1 << (12 - index)) - 1));
	}

	/*
	* compress_chunk
	*
	* Return:
	* * 0 - Ok, @cmpr contains @cmpr_chunk_size bytes of compressed data.
	* * 1 - Input buffer is full zero.
	* * -2 - The compressed buffer is too small to hold the compressed data.
	*/
	static inline int compress_chunk(size_t (match)(const u8 , struct lznt *),
	const u8 unc, const u8 unc_end, u8 *cmpr,
	u8 cmpr_end, size_t cmpr_chunk_size,
	struct lznt *ctx)
	{
	size_t cnt = 0;
	size_t idx = 0;
	const u8 *up = unc;
	u8 *cp = cmpr + 3;
	u8 *cp2 = cmpr + 2;
	u8 not_zero = 0;
	/* Control byte of 8-bit values: ( 0 - means byte as is, 1 - short pair ). */
	u8 ohdr = 0;
	u8 *last;
	u16 t16;

	if (unc + LZNT_CHUNK_SIZE < unc_end)
	unc_end = unc + LZNT_CHUNK_SIZE;

	last = min(cmpr + LZNT_CHUNK_SIZE + sizeof(short), cmpr_end);

	ctx->unc = unc;
	ctx->unc_end = unc_end;
	ctx->max_len = s_max_len[0];

	while (up < unc_end) {
	size_t max_len;

	while (unc + s_max_off[idx] < up)
	ctx->max_len = s_max_len[++idx];

	/* Find match. */
	max_len = up + 3 <= unc_end ? (*match)(up, ctx) : 0;

	if (!max_len) {
	if (cp >= last)
	goto NotCompressed;
	not_zero \|= cp++ = up++;
	} else if (cp + 1 >= last) {
	goto NotCompressed;
	} else {
	t16 = make_pair(up - ctx->best_match, max_len, idx);
	*cp++ = t16;
	*cp++ = t16 >> 8;

	ohdr \|= 1 << cnt;
	up += max_len;
	}

	cnt = (cnt + 1) & 7;
	if (!cnt) {
	*cp2 = ohdr;
	ohdr = 0;
	cp2 = cp;
	cp += 1;
	}
	}

	if (cp2 < last)
	*cp2 = ohdr;
	else
	cp -= 1;

	*cmpr_chunk_size = cp - cmpr;

	t16 = (*cmpr_chunk_size - 3) \| 0xB000;
	cmpr[0] = t16;
	cmpr[1] = t16 >> 8;

	return not_zero ? 0 : LZNT_ERROR_ALL_ZEROS;

	NotCompressed:

	if ((cmpr + LZNT_CHUNK_SIZE + sizeof(short)) > last)
	return -2;

	/*
	* Copy non cmpr data.
	* 0x3FFF == ((LZNT_CHUNK_SIZE + 2 - 3) \| 0x3000)
	*/
	cmpr[0] = 0xff;
	cmpr[1] = 0x3f;

	memcpy(cmpr + sizeof(short), unc, LZNT_CHUNK_SIZE);
	*cmpr_chunk_size = LZNT_CHUNK_SIZE + sizeof(short);

	return 0;
	}

	static inline ssize_t decompress_chunk(u8 unc, u8 unc_end, const u8 *cmpr,
	const u8 *cmpr_end)
	{
	u8 *up = unc;
	u8 ch = *cmpr++;
	size_t bit = 0;
	size_t index = 0;
	u16 pair;
	size_t offset, length;

	/* Do decompression until pointers are inside range. */
	while (up < unc_end && cmpr < cmpr_end) {
	/* Correct index */
	while (unc + s_max_off[index] < up)
	index += 1;

	/* Check the current flag for zero. */
	if (!(ch & (1 << bit))) {
	/* Just copy byte. */
	up++ = cmpr++;
	goto next;
	}

	/* Check for boundary. */
	if (cmpr + 1 >= cmpr_end)
	return -EINVAL;

	/* Read a short from little endian stream. */
	pair = cmpr[1];
	pair <<= 8;
	pair \|= cmpr[0];

	cmpr += 2;

	/* Translate packed information into offset and length. */
	length = parse_pair(pair, &offset, index);

	/* Check offset for boundary. */
	if (unc + offset > up)
	return -EINVAL;

	/* Truncate the length if necessary. */
	if (up + length >= unc_end)
	length = unc_end - up;

	/* Now we copy bytes. This is the heart of LZ algorithm. */
	for (; length > 0; length--, up++)
	up = (up - offset);

	next:
	/* Advance flag bit value. */
	bit = (bit + 1) & 7;

	if (!bit) {
	if (cmpr >= cmpr_end)
	break;

	ch = *cmpr++;
	}
	}

	/* Return the size of uncompressed data. */
	return up - unc;
	}

	/*
	* get_lznt_ctx
	* @level: 0 - Standard compression.
	* !0 - Best compression, requires a lot of cpu.
	*/
	struct lznt *get_lznt_ctx(int level)
	{
	struct lznt *r = kzalloc(level ? offsetof(struct lznt, hash) :
	sizeof(struct lznt),
	GFP_NOFS);

	if (r)
	r->std = !level;
	return r;
	}

	/*
	* compress_lznt - Compresses @unc into @cmpr
	*
	* Return:
	* * +x - Ok, @cmpr contains 'final_compressed_size' bytes of compressed data.
	* * 0 - Input buffer is full zero.
	*/
	size_t compress_lznt(const void unc, size_t unc_size, void cmpr,
	size_t cmpr_size, struct lznt *ctx)
	{
	int err;
	size_t (match)(const u8 src, struct lznt *ctx);
	u8 *p = cmpr;
	u8 *end = p + cmpr_size;
	const u8 *unc_chunk = unc;
	const u8 *unc_end = unc_chunk + unc_size;
	bool is_zero = true;

	if (ctx->std) {
	match = &longest_match_std;
	memset(ctx->hash, 0, sizeof(ctx->hash));
	} else {
	match = &longest_match_best;
	}

	/* Compression cycle. */
	for (; unc_chunk < unc_end; unc_chunk += LZNT_CHUNK_SIZE) {
	cmpr_size = 0;
	err = compress_chunk(match, unc_chunk, unc_end, p, end,
	&cmpr_size, ctx);
	if (err < 0)
	return unc_size;

	if (is_zero && err != LZNT_ERROR_ALL_ZEROS)
	is_zero = false;

	p += cmpr_size;
	}

	if (p <= end - 2)
	p[0] = p[1] = 0;

	return is_zero ? 0 : PtrOffset(cmpr, p);
	}

	/*
	* decompress_lznt - Decompress @cmpr into @unc.
	*/
	ssize_t decompress_lznt(const void cmpr, size_t cmpr_size, void unc,
	size_t unc_size)
	{
	const u8 *cmpr_chunk = cmpr;
	const u8 *cmpr_end = cmpr_chunk + cmpr_size;
	u8 *unc_chunk = unc;
	u8 *unc_end = unc_chunk + unc_size;
	u16 chunk_hdr;

	if (cmpr_size < sizeof(short))
	return -EINVAL;

	/* Read chunk header. */
	chunk_hdr = cmpr_chunk[1];
	chunk_hdr <<= 8;
	chunk_hdr \|= cmpr_chunk[0];

	/* Loop through decompressing chunks. */
	for (;;) {
	size_t chunk_size_saved;
	size_t unc_use;
	size_t cmpr_use = 3 + (chunk_hdr & (LZNT_CHUNK_SIZE - 1));

	/* Check that the chunk actually fits the supplied buffer. */
	if (cmpr_chunk + cmpr_use > cmpr_end)
	return -EINVAL;

	/* First make sure the chunk contains compressed data. */
	if (chunk_hdr & 0x8000) {
	/* Decompress a chunk and return if we get an error. */
	ssize_t err =
	decompress_chunk(unc_chunk, unc_end,
	cmpr_chunk + sizeof(chunk_hdr),
	cmpr_chunk + cmpr_use);
	if (err < 0)
	return err;
	unc_use = err;
	} else {
	/* This chunk does not contain compressed data. */
	unc_use = unc_chunk + LZNT_CHUNK_SIZE > unc_end ?
	unc_end - unc_chunk :
	LZNT_CHUNK_SIZE;

	if (cmpr_chunk + sizeof(chunk_hdr) + unc_use >
	cmpr_end) {
	return -EINVAL;
	}

	memcpy(unc_chunk, cmpr_chunk + sizeof(chunk_hdr),
	unc_use);
	}

	/* Advance pointers. */
	cmpr_chunk += cmpr_use;
	unc_chunk += unc_use;

	/* Check for the end of unc buffer. */
	if (unc_chunk >= unc_end)
	break;

	/* Proceed the next chunk. */
	if (cmpr_chunk > cmpr_end - 2)
	break;

	chunk_size_saved = LZNT_CHUNK_SIZE;

	/* Read chunk header. */
	chunk_hdr = cmpr_chunk[1];
	chunk_hdr <<= 8;
	chunk_hdr \|= cmpr_chunk[0];

	if (!chunk_hdr)
	break;

	/* Check the size of unc buffer. */
	if (unc_use < chunk_size_saved) {
	size_t t1 = chunk_size_saved - unc_use;
	u8 *t2 = unc_chunk + t1;

	/* 'Zero' memory. */
	if (t2 >= unc_end)
	break;

	memset(unc_chunk, 0, t1);
	unc_chunk = t2;
	}
	}

	/* Check compression boundary. */
	if (cmpr_chunk > cmpr_end)
	return -EINVAL;

	/*
	* The unc size is just a difference between current
	* pointer and original one.
	*/
	return PtrOffset(unc, unc_chunk);
	}