1 files changed, 338 insertions, 0 deletions
diff --git a/fs/ntfs3/lib/decompress_common.h b/fs/ntfs3/lib/decompress_common.h
new file mode 100644
index 000000000000..2d70ae42f1b5
--- /dev/null
+++ b/fs/ntfs3/lib/decompress_common.h
@@ -0,0 +1,338 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * decompress_common.h - Code shared by the XPRESS and LZX decompressors
+ *
+ * Copyright (C) 2015 Eric Biggers
+ */
+
+#include <linux/string.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <asm/unaligned.h>
+
+
+/* "Force inline" macro (not required, but helpful for performance)  */
+#define forceinline __always_inline
+
+/* Enable whole-word match copying on selected architectures  */
+#if defined(__i386__) || defined(__x86_64__) || defined(__ARM_FEATURE_UNALIGNED)
+#  define FAST_UNALIGNED_ACCESS
+#endif
+
+/* Size of a machine word  */
+#define WORDBYTES (sizeof(size_t))
+
+static forceinline void
+copy_unaligned_word(const void *src, void *dst)
+{
+	put_unaligned(get_unaligned((const size_t *)src), (size_t *)dst);
+}
+
+
+/* Generate a "word" with platform-dependent size whose bytes all contain the
+ * value 'b'.
+ */
+static forceinline size_t repeat_byte(u8 b)
+{
+	size_t v;
+
+	v = b;
+	v |= v << 8;
+	v |= v << 16;
+	v |= v << ((WORDBYTES == 8) ? 32 : 0);
+	return v;
+}
+
+/* Structure that encapsulates a block of in-memory data being interpreted as a
+ * stream of bits, optionally with interwoven literal bytes.  Bits are assumed
+ * to be stored in little endian 16-bit coding units, with the bits ordered high
+ * to low.
+ */
+struct input_bitstream {
+
+	/* Bits that have been read from the input buffer.  The bits are
+	 * left-justified; the next bit is always bit 31.
+	 */
+	u32 bitbuf;
+
+	/* Number of bits currently held in @bitbuf.  */
+	u32 bitsleft;
+
+	/* Pointer to the next byte to be retrieved from the input buffer.  */
+	const u8 *next;
+
+	/* Pointer to just past the end of the input buffer.  */
+	const u8 *end;
+};
+
+/* Initialize a bitstream to read from the specified input buffer.  */
+static forceinline void init_input_bitstream(struct input_bitstream *is,
+					     const void *buffer, u32 size)
+{
+	is->bitbuf = 0;
+	is->bitsleft = 0;
+	is->next = buffer;
+	is->end = is->next + size;
+}
+
+/* Ensure the bit buffer variable for the bitstream contains at least @num_bits
+ * bits.  Following this, bitstream_peek_bits() and/or bitstream_remove_bits()
+ * may be called on the bitstream to peek or remove up to @num_bits bits.  Note
+ * that @num_bits must be <= 16.
+ */
+static forceinline void bitstream_ensure_bits(struct input_bitstream *is,
+					      u32 num_bits)
+{
+	if (is->bitsleft < num_bits) {
+		if (is->end - is->next >= 2) {
+			is->bitbuf |= (u32)get_unaligned_le16(is->next)
+					<< (16 - is->bitsleft);
+			is->next += 2;
+		}
+		is->bitsleft += 16;
+	}
+}
+
+/* Return the next @num_bits bits from the bitstream, without removing them.
+ * There must be at least @num_bits remaining in the buffer variable, from a
+ * previous call to bitstream_ensure_bits().
+ */
+static forceinline u32
+bitstream_peek_bits(const struct input_bitstream *is, const u32 num_bits)
+{
+	return (is->bitbuf >> 1) >> (sizeof(is->bitbuf) * 8 - num_bits - 1);
+}
+
+/* Remove @num_bits from the bitstream.  There must be at least @num_bits
+ * remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits().
+ */
+static forceinline void
+bitstream_remove_bits(struct input_bitstream *is, u32 num_bits)
+{
+	is->bitbuf <<= num_bits;
+	is->bitsleft -= num_bits;
+}
+
+/* Remove and return @num_bits bits from the bitstream.  There must be at least
+ * @num_bits remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits().
+ */
+static forceinline u32
+bitstream_pop_bits(struct input_bitstream *is, u32 num_bits)
+{
+	u32 bits = bitstream_peek_bits(is, num_bits);
+
+	bitstream_remove_bits(is, num_bits);
+	return bits;
+}
+
+/* Read and return the next @num_bits bits from the bitstream.  */
+static forceinline u32
+bitstream_read_bits(struct input_bitstream *is, u32 num_bits)
+{
+	bitstream_ensure_bits(is, num_bits);
+	return bitstream_pop_bits(is, num_bits);
+}
+
+/* Read and return the next literal byte embedded in the bitstream.  */
+static forceinline u8
+bitstream_read_byte(struct input_bitstream *is)
+{
+	if (unlikely(is->end == is->next))
+		return 0;
+	return *is->next++;
+}
+
+/* Read and return the next 16-bit integer embedded in the bitstream.  */
+static forceinline u16
+bitstream_read_u16(struct input_bitstream *is)
+{
+	u16 v;
+
+	if (unlikely(is->end - is->next < 2))
+		return 0;
+	v = get_unaligned_le16(is->next);
+	is->next += 2;
+	return v;
+}
+
+/* Read and return the next 32-bit integer embedded in the bitstream.  */
+static forceinline u32
+bitstream_read_u32(struct input_bitstream *is)
+{
+	u32 v;
+
+	if (unlikely(is->end - is->next < 4))
+		return 0;
+	v = get_unaligned_le32(is->next);
+	is->next += 4;
+	return v;
+}
+
+/* Read into @dst_buffer an array of literal bytes embedded in the bitstream.
+ * Return either a pointer to the byte past the last written, or NULL if the
+ * read overflows the input buffer.
+ */
+static forceinline void *bitstream_read_bytes(struct input_bitstream *is,
+					      void *dst_buffer, size_t count)
+{
+	if ((size_t)(is->end - is->next) < count)
+		return NULL;
+	memcpy(dst_buffer, is->next, count);
+	is->next += count;
+	return (u8 *)dst_buffer + count;
+}
+
+/* Align the input bitstream on a coding-unit boundary.  */
+static forceinline void bitstream_align(struct input_bitstream *is)
+{
+	is->bitsleft = 0;
+	is->bitbuf = 0;
+}
+
+extern int make_huffman_decode_table(u16 decode_table[], const u32 num_syms,
+				     const u32 num_bits, const u8 lens[],
+				     const u32 max_codeword_len,
+				     u16 working_space[]);
+
+
+/* Reads and returns the next Huffman-encoded symbol from a bitstream.  If the
+ * input data is exhausted, the Huffman symbol is decoded as if the missing bits
+ * are all zeroes.
+ */
+static forceinline u32 read_huffsym(struct input_bitstream *istream,
+					 const u16 decode_table[],
+					 u32 table_bits,
+					 u32 max_codeword_len)
+{
+	u32 entry;
+	u32 key_bits;
+
+	bitstream_ensure_bits(istream, max_codeword_len);
+
+	/* Index the decode table by the next table_bits bits of the input.  */
+	key_bits = bitstream_peek_bits(istream, table_bits);
+	entry = decode_table[key_bits];
+	if (entry < 0xC000) {
+		/* Fast case: The decode table directly provided the
+		 * symbol and codeword length.  The low 11 bits are the
+		 * symbol, and the high 5 bits are the codeword length.
+		 */
+		bitstream_remove_bits(istream, entry >> 11);
+		return entry & 0x7FF;
+	}
+	/* Slow case: The codeword for the symbol is longer than
+	 * table_bits, so the symbol does not have an entry
+	 * directly in the first (1 << table_bits) entries of the
+	 * decode table.  Traverse the appropriate binary tree
+	 * bit-by-bit to decode the symbol.
+	 */
+	bitstream_remove_bits(istream, table_bits);
+	do {
+		key_bits = (entry & 0x3FFF) + bitstream_pop_bits(istream, 1);
+	} while ((entry = decode_table[key_bits]) >= 0xC000);
+	return entry;
+}
+
+/*
+ * Copy an LZ77 match at (dst - offset) to dst.
+ *
+ * The length and offset must be already validated --- that is, (dst - offset)
+ * can't underrun the output buffer, and (dst + length) can't overrun the output
+ * buffer.  Also, the length cannot be 0.
+ *
+ * @bufend points to the byte past the end of the output buffer.  This function
+ * won't write any data beyond this position.
+ *
+ * Returns dst + length.
+ */
+static forceinline u8 *lz_copy(u8 *dst, u32 length, u32 offset, const u8 *bufend,
+			       u32 min_length)
+{
+	const u8 *src = dst - offset;
+
+	/*
+	 * Try to copy one machine word at a time.  On i386 and x86_64 this is
+	 * faster than copying one byte at a time, unless the data is
+	 * near-random and all the matches have very short lengths.  Note that
+	 * since this requires unaligned memory accesses, it won't necessarily
+	 * be faster on every architecture.
+	 *
+	 * Also note that we might copy more than the length of the match.  For
+	 * example, if a word is 8 bytes and the match is of length 5, then
+	 * we'll simply copy 8 bytes.  This is okay as long as we don't write
+	 * beyond the end of the output buffer, hence the check for (bufend -
+	 * end >= WORDBYTES - 1).
+	 */
+#ifdef FAST_UNALIGNED_ACCESS
+	u8 * const end = dst + length;
+
+	if (bufend - end >= (ptrdiff_t)(WORDBYTES - 1)) {
+
+		if (offset >= WORDBYTES) {
+			/* The source and destination words don't overlap.  */
+
+			/* To improve branch prediction, one iteration of this
+			 * loop is unrolled.  Most matches are short and will
+			 * fail the first check.  But if that check passes, then
+			 * it becomes increasing likely that the match is long
+			 * and we'll need to continue copying.
+			 */
+
+			copy_unaligned_word(src, dst);
+			src += WORDBYTES;
+			dst += WORDBYTES;
+
+			if (dst < end) {
+				do {
+					copy_unaligned_word(src, dst);
+					src += WORDBYTES;
+					dst += WORDBYTES;
+				} while (dst < end);
+			}
+			return end;
+		} else if (offset == 1) {
+
+			/* Offset 1 matches are equivalent to run-length
+			 * encoding of the previous byte.  This case is common
+			 * if the data contains many repeated bytes.
+			 */
+			size_t v = repeat_byte(*(dst - 1));
+
+			do {
+				put_unaligned(v, (size_t *)dst);
+				src += WORDBYTES;
+				dst += WORDBYTES;
+			} while (dst < end);
+			return end;
+		}
+		/*
+		 * We don't bother with special cases for other 'offset <
+		 * WORDBYTES', which are usually rarer than 'offset == 1'.  Extra
+		 * checks will just slow things down.  Actually, it's possible
+		 * to handle all the 'offset < WORDBYTES' cases using the same
+		 * code, but it still becomes more complicated doesn't seem any
+		 * faster overall; it definitely slows down the more common
+		 * 'offset == 1' case.
+		 */
+	}
+#endif /* FAST_UNALIGNED_ACCESS */
+
+	/* Fall back to a bytewise copy.  */
+
+	if (min_length >= 2) {
+		*dst++ = *src++;
+		length--;
+	}
+	if (min_length >= 3) {
+		*dst++ = *src++;
+		length--;
+	}
+	do {
+		*dst++ = *src++;
+	} while (--length);
+
+	return dst;
+}