chromium/third_party/snappy/src/snappy.cc

// Copyright 2005 Google Inc. All Rights Reserved.
//
// 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.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// 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.

#include "snappy-internal.h"
#include "snappy-sinksource.h"
#include "snappy.h"
#if !defined(SNAPPY_HAVE_BMI2)
// __BMI2__ is defined by GCC and Clang. Visual Studio doesn't target BMI2
// specifically, but it does define __AVX2__ when AVX2 support is available.
// Fortunately, AVX2 was introduced in Haswell, just like BMI2.
//
// BMI2 is not defined as a subset of AVX2 (unlike SSSE3 and AVX above). So,
// GCC and Clang can build code with AVX2 enabled but BMI2 disabled, in which
// case issuing BMI2 instructions results in a compiler error.
#if defined(__BMI2__) || (defined(_MSC_VER) && defined(__AVX2__))
#define SNAPPY_HAVE_BMI2 …
#else
#define SNAPPY_HAVE_BMI2 …
#endif
#endif  // !defined(SNAPPY_HAVE_BMI2)

#if !defined(SNAPPY_HAVE_X86_CRC32)
#if defined(__SSE4_2__)
#define SNAPPY_HAVE_X86_CRC32 …
#else
#define SNAPPY_HAVE_X86_CRC32 …
#endif
#endif  // !defined(SNAPPY_HAVE_X86_CRC32)

#if !defined(SNAPPY_HAVE_NEON_CRC32)
#if SNAPPY_HAVE_NEON && defined(__ARM_FEATURE_CRC32)
#define SNAPPY_HAVE_NEON_CRC32 …
#else
#define SNAPPY_HAVE_NEON_CRC32 …
#endif
#endif  // !defined(SNAPPY_HAVE_NEON_CRC32)

#if SNAPPY_HAVE_BMI2 || SNAPPY_HAVE_X86_CRC32
// Please do not replace with <x86intrin.h>. or with headers that assume more
// advanced SSE versions without checking with all the OWNERS.
#include <immintrin.h>
#elif SNAPPY_HAVE_NEON_CRC32
#include <arm_acle.h>
#endif

#include <algorithm>
#include <array>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <string>
#include <utility>
#include <vector>

namespace snappy {

namespace {

// The amount of slop bytes writers are using for unconditional copies.
constexpr int kSlopBytes = …;

char_table;
COPY_1_BYTE_OFFSET;
COPY_2_BYTE_OFFSET;
COPY_4_BYTE_OFFSET;
kMaximumTagLength;
LITERAL;
#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
using internal::V128;
using internal::V128_Load;
using internal::V128_LoadU;
using internal::V128_Shuffle;
using internal::V128_StoreU;
using internal::V128_DupChar;
#endif

// We translate the information encoded in a tag through a lookup table to a
// format that requires fewer instructions to decode. Effectively we store
// the length minus the tag part of the offset. The lowest significant byte
// thus stores the length. While total length - offset is given by
// entry - ExtractOffset(type). The nice thing is that the subtraction
// immediately sets the flags for the necessary check that offset >= length.
// This folds the cmp with sub. We engineer the long literals and copy-4 to
// always fail this check, so their presence doesn't affect the fast path.
// To prevent literals from triggering the guard against offset < length (offset
// does not apply to literals) the table is giving them a spurious offset of
// 256.
inline constexpr int16_t MakeEntry(int16_t len, int16_t offset) { … }

inline constexpr int16_t LengthMinusOffset(int data, int type) { … }

inline constexpr int16_t LengthMinusOffset(uint8_t tag) { … }

template <size_t... Ints>
struct index_sequence { … };

template <std::size_t N, size_t... Is>
struct make_index_sequence : make_index_sequence<N - 1, N - 1, Is...> { … };

make_index_sequence<0, Is...>;

template <size_t... seq>
constexpr std::array<int16_t, 256> MakeTable(index_sequence<seq...>) { … }

alignas(64) const std::array<int16_t, 256> kLengthMinusOffset = …;

// Given a table of uint16_t whose size is mask / 2 + 1, return a pointer to the
// relevant entry, if any, for the given bytes.  Any hash function will do,
// but a good hash function reduces the number of collisions and thus yields
// better compression for compressible input.
//
// REQUIRES: mask is 2 * (table_size - 1), and table_size is a power of two.
inline uint16_t* TableEntry(uint16_t* table, uint32_t bytes, uint32_t mask) { … }

}  // namespace

size_t MaxCompressedLength(size_t source_bytes) { … }

namespace {

void UnalignedCopy64(const void* src, void* dst) { … }

void UnalignedCopy128(const void* src, void* dst) { … }

template <bool use_16bytes_chunk>
inline void ConditionalUnalignedCopy128(const char* src, char* dst) { … }

// Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) a byte at a time. Used
// for handling COPY operations where the input and output regions may overlap.
// For example, suppose:
//    src       == "ab"
//    op        == src + 2
//    op_limit  == op + 20
// After IncrementalCopySlow(src, op, op_limit), the result will have eleven
// copies of "ab"
//    ababababababababababab
// Note that this does not match the semantics of either std::memcpy() or
// std::memmove().
inline char* IncrementalCopySlow(const char* src, char* op,
                                 char* const op_limit) { … }

#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE

// Computes the bytes for shuffle control mask (please read comments on
// 'pattern_generation_masks' as well) for the given index_offset and
// pattern_size. For example, when the 'offset' is 6, it will generate a
// repeating pattern of size 6. So, the first 16 byte indexes will correspond to
// the pattern-bytes {0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3} and the
// next 16 byte indexes will correspond to the pattern-bytes {4, 5, 0, 1, 2, 3,
// 4, 5, 0, 1, 2, 3, 4, 5, 0, 1}. These byte index sequences are generated by
// calling MakePatternMaskBytes(0, 6, index_sequence<16>()) and
// MakePatternMaskBytes(16, 6, index_sequence<16>()) respectively.
template <size_t... indexes>
inline constexpr std::array<char, sizeof...(indexes)> MakePatternMaskBytes(
    int index_offset, int pattern_size, index_sequence<indexes...>) {
  return {static_cast<char>((index_offset + indexes) % pattern_size)...};
}

// Computes the shuffle control mask bytes array for given pattern-sizes and
// returns an array.
template <size_t... pattern_sizes_minus_one>
inline constexpr std::array<std::array<char, sizeof(V128)>,
                            sizeof...(pattern_sizes_minus_one)>
MakePatternMaskBytesTable(int index_offset,
                          index_sequence<pattern_sizes_minus_one...>) {
  return {
      MakePatternMaskBytes(index_offset, pattern_sizes_minus_one + 1,
                           make_index_sequence</*indexes=*/sizeof(V128)>())...};
}

// This is an array of shuffle control masks that can be used as the source
// operand for PSHUFB to permute the contents of the destination XMM register
// into a repeating byte pattern.
alignas(16) constexpr std::array<std::array<char, sizeof(V128)>,
                                 16> pattern_generation_masks =
    MakePatternMaskBytesTable(
        /*index_offset=*/0,
        /*pattern_sizes_minus_one=*/make_index_sequence<16>());

// Similar to 'pattern_generation_masks', this table is used to "rotate" the
// pattern so that we can copy the *next 16 bytes* consistent with the pattern.
// Basically, pattern_reshuffle_masks is a continuation of
// pattern_generation_masks. It follows that, pattern_reshuffle_masks is same as
// pattern_generation_masks for offsets 1, 2, 4, 8 and 16.
alignas(16) constexpr std::array<std::array<char, sizeof(V128)>,
                                 16> pattern_reshuffle_masks =
    MakePatternMaskBytesTable(
        /*index_offset=*/16,
        /*pattern_sizes_minus_one=*/make_index_sequence<16>());

SNAPPY_ATTRIBUTE_ALWAYS_INLINE
static inline V128 LoadPattern(const char* src, const size_t pattern_size) {
  V128 generation_mask = V128_Load(reinterpret_cast<const V128*>(
      pattern_generation_masks[pattern_size - 1].data()));
  // Uninitialized bytes are masked out by the shuffle mask.
  // TODO: remove annotation and macro defs once MSan is fixed.
  SNAPPY_ANNOTATE_MEMORY_IS_INITIALIZED(src + pattern_size, 16 - pattern_size);
  return V128_Shuffle(V128_LoadU(reinterpret_cast<const V128*>(src)),
                      generation_mask);
}

SNAPPY_ATTRIBUTE_ALWAYS_INLINE
static inline std::pair<V128 /* pattern */, V128 /* reshuffle_mask */>
LoadPatternAndReshuffleMask(const char* src, const size_t pattern_size) {
  V128 pattern = LoadPattern(src, pattern_size);

  // This mask will generate the next 16 bytes in-place. Doing so enables us to
  // write data by at most 4 V128_StoreU.
  //
  // For example, suppose pattern is:        abcdefabcdefabcd
  // Shuffling with this mask will generate: efabcdefabcdefab
  // Shuffling again will generate:          cdefabcdefabcdef
  V128 reshuffle_mask = V128_Load(reinterpret_cast<const V128*>(
      pattern_reshuffle_masks[pattern_size - 1].data()));
  return {pattern, reshuffle_mask};
}

#endif  // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE

// Fallback for when we need to copy while extending the pattern, for example
// copying 10 bytes from 3 positions back abc -> abcabcabcabca.
//
// REQUIRES: [dst - offset, dst + 64) is a valid address range.
SNAPPY_ATTRIBUTE_ALWAYS_INLINE
static inline bool Copy64BytesWithPatternExtension(char* dst, size_t offset) { … }

// Copy [src, src+(op_limit-op)) to [op, op_limit) but faster than
// IncrementalCopySlow. buf_limit is the address past the end of the writable
// region of the buffer.
inline char* IncrementalCopy(const char* src, char* op, char* const op_limit,
                             char* const buf_limit) { … }

}  // namespace

template <bool allow_fast_path>
static inline char* EmitLiteral(char* op, const char* literal, int len) { … }

template <bool len_less_than_12>
static inline char* EmitCopyAtMost64(char* op, size_t offset, size_t len) { … }

template <bool len_less_than_12>
static inline char* EmitCopy(char* op, size_t offset, size_t len) { … }

bool GetUncompressedLength(const char* start, size_t n, size_t* result) { … }

namespace {
uint32_t CalculateTableSize(uint32_t input_size) { … }
}  // namespace

namespace internal {
WorkingMemory::WorkingMemory(size_t input_size) { … }

WorkingMemory::~WorkingMemory() { … }

uint16_t* WorkingMemory::GetHashTable(size_t fragment_size,
                                      int* table_size) const { … }
}  // end namespace internal

// Flat array compression that does not emit the "uncompressed length"
// prefix. Compresses "input" string to the "*op" buffer.
//
// REQUIRES: "input" is at most "kBlockSize" bytes long.
// REQUIRES: "op" points to an array of memory that is at least
// "MaxCompressedLength(input.size())" in size.
// REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
// REQUIRES: "table_size" is a power of two
//
// Returns an "end" pointer into "op" buffer.
// "end - op" is the compressed size of "input".
namespace internal {
char* CompressFragment(const char* input, size_t input_size, char* op,
                       uint16_t* table, const int table_size) { … }
}  // end namespace internal

// Called back at avery compression call to trace parameters and sizes.
static inline void Report(const char *algorithm, size_t compressed_size,
                          size_t uncompressed_size) { … }

// Signature of output types needed by decompression code.
// The decompression code is templatized on a type that obeys this
// signature so that we do not pay virtual function call overhead in
// the middle of a tight decompression loop.
//
// class DecompressionWriter {
//  public:
//   // Called before decompression
//   void SetExpectedLength(size_t length);
//
//   // For performance a writer may choose to donate the cursor variable to the
//   // decompression function. The decompression will inject it in all its
//   // function calls to the writer. Keeping the important output cursor as a
//   // function local stack variable allows the compiler to keep it in
//   // register, which greatly aids performance by avoiding loads and stores of
//   // this variable in the fast path loop iterations.
//   T GetOutputPtr() const;
//
//   // At end of decompression the loop donates the ownership of the cursor
//   // variable back to the writer by calling this function.
//   void SetOutputPtr(T op);
//
//   // Called after decompression
//   bool CheckLength() const;
//
//   // Called repeatedly during decompression
//   // Each function get a pointer to the op (output pointer), that the writer
//   // can use and update. Note it's important that these functions get fully
//   // inlined so that no actual address of the local variable needs to be
//   // taken.
//   bool Append(const char* ip, size_t length, T* op);
//   bool AppendFromSelf(uint32_t offset, size_t length, T* op);
//
//   // The rules for how TryFastAppend differs from Append are somewhat
//   // convoluted:
//   //
//   //  - TryFastAppend is allowed to decline (return false) at any
//   //    time, for any reason -- just "return false" would be
//   //    a perfectly legal implementation of TryFastAppend.
//   //    The intention is for TryFastAppend to allow a fast path
//   //    in the common case of a small append.
//   //  - TryFastAppend is allowed to read up to <available> bytes
//   //    from the input buffer, whereas Append is allowed to read
//   //    <length>. However, if it returns true, it must leave
//   //    at least five (kMaximumTagLength) bytes in the input buffer
//   //    afterwards, so that there is always enough space to read the
//   //    next tag without checking for a refill.
//   //  - TryFastAppend must always return decline (return false)
//   //    if <length> is 61 or more, as in this case the literal length is not
//   //    decoded fully. In practice, this should not be a big problem,
//   //    as it is unlikely that one would implement a fast path accepting
//   //    this much data.
//   //
//   bool TryFastAppend(const char* ip, size_t available, size_t length, T* op);
// };

static inline uint32_t ExtractLowBytes(const uint32_t& v, int n) { … }

static inline bool LeftShiftOverflows(uint8_t value, uint32_t shift) { … }

inline bool Copy64BytesWithPatternExtension(ptrdiff_t dst, size_t offset) { … }

// Copies between size bytes and 64 bytes from src to dest.  size cannot exceed
// 64.  More than size bytes, but never exceeding 64, might be copied if doing
// so gives better performance.  [src, src + size) must not overlap with
// [dst, dst + size), but [src, src + 64) may overlap with [dst, dst + 64).
void MemCopy64(char* dst, const void* src, size_t size) { … }

void MemCopy64(ptrdiff_t dst, const void* src, size_t size) { … }

void ClearDeferred(const void** deferred_src, size_t* deferred_length,
                   uint8_t* safe_source) { … }

void DeferMemCopy(const void** deferred_src, size_t* deferred_length,
                  const void* src, size_t length) { … }

SNAPPY_ATTRIBUTE_ALWAYS_INLINE
inline size_t AdvanceToNextTagARMOptimized(const uint8_t** ip_p, size_t* tag) { … }

SNAPPY_ATTRIBUTE_ALWAYS_INLINE
inline size_t AdvanceToNextTagX86Optimized(const uint8_t** ip_p, size_t* tag) { … }

// Extract the offset for copy-1 and copy-2 returns 0 for literals or copy-4.
inline uint32_t ExtractOffset(uint32_t val, size_t tag_type) {
  // For x86 non-static storage works better. For ARM static storage is better.
  // TODO: Once the array is recognized as a register, improve the
  // readability for x86.
#if defined(__x86_64__)
  constexpr uint64_t kExtractMasksCombined = 0x0000FFFF00FF0000ull;
  uint16_t result;
  memcpy(&result,
         reinterpret_cast<const char*>(&kExtractMasksCombined) + 2 * tag_type,
         sizeof(result));
  return val & result;
#elif defined(__aarch64__)
  constexpr uint64_t kExtractMasksCombined = 0x0000FFFF00FF0000ull;
  return val & static_cast<uint32_t>(
      (kExtractMasksCombined >> (tag_type * 16)) & 0xFFFF);
#else
  static constexpr uint32_t kExtractMasks[4] = {0, 0xFF, 0xFFFF, 0};
  return val & kExtractMasks[tag_type];
#endif
};

// Core decompression loop, when there is enough data available.
// Decompresses the input buffer [ip, ip_limit) into the output buffer
// [op, op_limit_min_slop). Returning when either we are too close to the end
// of the input buffer, or we exceed op_limit_min_slop or when a exceptional
// tag is encountered (literal of length > 60) or a copy-4.
// Returns {ip, op} at the points it stopped decoding.
// TODO This function probably does not need to be inlined, as it
// should decode large chunks at a time. This allows runtime dispatch to
// implementations based on CPU capability (BMI2 / perhaps 32 / 64 byte memcpy).
template <typename T>
std::pair<const uint8_t*, ptrdiff_t> DecompressBranchless(
    const uint8_t* ip, const uint8_t* ip_limit, ptrdiff_t op, T op_base,
    ptrdiff_t op_limit_min_slop) { … }

// Helper class for decompression
class SnappyDecompressor { … };

constexpr uint32_t CalculateNeeded(uint8_t tag) { … }

#if __cplusplus >= 201402L
constexpr bool VerifyCalculateNeeded() { … }

// Make sure CalculateNeeded is correct by verifying it against the established
// table encoding the number of added bytes needed.
static_assert …;
#endif  // c++14

bool SnappyDecompressor::RefillTag() { … }

template <typename Writer>
static bool InternalUncompress(Source* r, Writer* writer) { … }

template <typename Writer>
static bool InternalUncompressAllTags(SnappyDecompressor* decompressor,
                                      Writer* writer, uint32_t compressed_len,
                                      uint32_t uncompressed_len) { … }

bool GetUncompressedLength(Source* source, uint32_t* result) { … }

size_t Compress(Source* reader, Sink* writer) { … }

// -----------------------------------------------------------------------
// IOVec interfaces
// -----------------------------------------------------------------------

// A `Source` implementation that yields the contents of an `iovec` array. Note
// that `total_size` is the total number of bytes to be read from the elements
// of `iov` (_not_ the total number of elements in `iov`).
class SnappyIOVecReader : public Source { … };

// A type that writes to an iovec.
// Note that this is not a "ByteSink", but a type that matches the
// Writer template argument to SnappyDecompressor::DecompressAllTags().
class SnappyIOVecWriter { … };

bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
                          const struct iovec* iov, size_t iov_cnt) { … }

bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov,
                          size_t iov_cnt) { … }

// -----------------------------------------------------------------------
// Flat array interfaces
// -----------------------------------------------------------------------

// A type that writes to a flat array.
// Note that this is not a "ByteSink", but a type that matches the
// Writer template argument to SnappyDecompressor::DecompressAllTags().
class SnappyArrayWriter { … };

bool RawUncompress(const char* compressed, size_t compressed_length,
                   char* uncompressed) { … }

bool RawUncompress(Source* compressed, char* uncompressed) { … }

bool Uncompress(const char* compressed, size_t compressed_length,
                std::string* uncompressed) { … }

// A Writer that drops everything on the floor and just does validation
class SnappyDecompressionValidator { … };

bool IsValidCompressedBuffer(const char* compressed, size_t compressed_length) { … }

bool IsValidCompressed(Source* compressed) { … }

void RawCompress(const char* input, size_t input_length, char* compressed,
                 size_t* compressed_length) { … }

void RawCompressFromIOVec(const struct iovec* iov, size_t uncompressed_length,
                          char* compressed, size_t* compressed_length) { … }

size_t Compress(const char* input, size_t input_length,
                std::string* compressed) { … }

size_t CompressFromIOVec(const struct iovec* iov, size_t iov_cnt,
                         std::string* compressed) { … }

// -----------------------------------------------------------------------
// Sink interface
// -----------------------------------------------------------------------

// A type that decompresses into a Sink. The template parameter
// Allocator must export one method "char* Allocate(int size);", which
// allocates a buffer of "size" and appends that to the destination.
template <typename Allocator>
class SnappyScatteredWriter { … };

template <typename Allocator>
bool SnappyScatteredWriter<Allocator>::SlowAppend(const char* ip, size_t len) { … }

template <typename Allocator>
bool SnappyScatteredWriter<Allocator>::SlowAppendFromSelf(size_t offset,
                                                         size_t len) { … }

class SnappySinkAllocator { … };

size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed) { … }

bool Uncompress(Source* compressed, Sink* uncompressed) { … }

}  // namespace snappy