665 lines
18 KiB
C++
665 lines
18 KiB
C++
/*
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* Copyright 2012-present Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <cstdint>
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#include <limits>
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#include <glog/logging.h>
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#if !defined(__GNUC__) && !defined(_MSC_VER)
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#error GroupVarint.h requires GCC or MSVC
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#endif
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#include <folly/Portability.h>
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#if FOLLY_X64 || defined(__i386__) || FOLLY_PPC64 || FOLLY_AARCH64
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#define HAVE_GROUP_VARINT 1
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#include <folly/Range.h>
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#include <folly/detail/GroupVarintDetail.h>
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#include <folly/lang/Bits.h>
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#include <folly/portability/Builtins.h>
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#if FOLLY_SSE >= 3
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#include <nmmintrin.h>
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namespace folly {
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namespace detail {
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extern const std::array<std::array<std::uint32_t, 4>, 256> groupVarintSSEMasks;
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} // namespace detail
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} // namespace folly
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#endif
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namespace folly {
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namespace detail {
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extern const std::array<std::uint8_t, 256> groupVarintLengths;
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} // namespace detail
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} // namespace folly
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namespace folly {
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template <typename T>
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class GroupVarint;
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/**
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* GroupVarint encoding for 32-bit values.
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*
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* Encodes 4 32-bit integers at once, each using 1-4 bytes depending on size.
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* There is one byte of overhead. (The first byte contains the lengths of
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* the four integers encoded as two bits each; 00=1 byte .. 11=4 bytes)
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*
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* This implementation assumes little-endian and does unaligned 32-bit
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* accesses, so it's basically not portable outside of the x86[_64] world.
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*/
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template <>
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class GroupVarint<uint32_t> : public detail::GroupVarintBase<uint32_t> {
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public:
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/**
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* Return the number of bytes used to encode these four values.
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*/
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static size_t size(uint32_t a, uint32_t b, uint32_t c, uint32_t d) {
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return kHeaderSize + kGroupSize + key(a) + key(b) + key(c) + key(d);
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}
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/**
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* Return the number of bytes used to encode four uint32_t values stored
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* at consecutive positions in an array.
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*/
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static size_t size(const uint32_t* p) {
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return size(p[0], p[1], p[2], p[3]);
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}
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/**
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* Return the number of bytes used to encode count (<= 4) values.
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* If you clip a buffer after these many bytes, you can still decode
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* the first "count" values correctly (if the remaining size() -
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* partialSize() bytes are filled with garbage).
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*/
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static size_t partialSize(const type* p, size_t count) {
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DCHECK_LE(count, kGroupSize);
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size_t s = kHeaderSize + count;
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for (; count; --count, ++p) {
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s += key(*p);
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}
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return s;
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}
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/**
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* Return the number of values from *p that are valid from an encoded
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* buffer of size bytes.
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*/
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static size_t partialCount(const char* p, size_t size) {
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uint8_t v = uint8_t(*p);
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size_t s = kHeaderSize;
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s += 1 + b0key(v);
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if (s > size) {
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return 0;
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}
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s += 1 + b1key(v);
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if (s > size) {
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return 1;
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}
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s += 1 + b2key(v);
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if (s > size) {
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return 2;
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}
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s += 1 + b3key(v);
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if (s > size) {
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return 3;
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}
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return 4;
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}
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/**
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* Given a pointer to the beginning of an GroupVarint32-encoded block,
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* return the number of bytes used by the encoding.
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*/
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static size_t encodedSize(const char* p) {
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return kHeaderSize + kGroupSize + b0key(uint8_t(*p)) + b1key(uint8_t(*p)) +
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b2key(uint8_t(*p)) + b3key(uint8_t(*p));
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}
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/**
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* Encode four uint32_t values into the buffer pointed-to by p, and return
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* the next position in the buffer (that is, one character past the last
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* encoded byte). p needs to have at least size()+4 bytes available.
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*/
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static char* encode(char* p, uint32_t a, uint32_t b, uint32_t c, uint32_t d) {
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uint8_t b0key = key(a);
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uint8_t b1key = key(b);
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uint8_t b2key = key(c);
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uint8_t b3key = key(d);
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*p++ = (b3key << 6) | (b2key << 4) | (b1key << 2) | b0key;
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storeUnaligned(p, a);
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p += b0key + 1;
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storeUnaligned(p, b);
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p += b1key + 1;
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storeUnaligned(p, c);
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p += b2key + 1;
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storeUnaligned(p, d);
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p += b3key + 1;
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return p;
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}
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/**
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* Encode four uint32_t values from the array pointed-to by src into the
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* buffer pointed-to by p, similar to encode(p,a,b,c,d) above.
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*/
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static char* encode(char* p, const uint32_t* src) {
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return encode(p, src[0], src[1], src[2], src[3]);
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}
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/**
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* Decode four uint32_t values from a buffer, and return the next position
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* in the buffer (that is, one character past the last encoded byte).
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* The buffer needs to have at least 3 extra bytes available (they
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* may be read but ignored).
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*/
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static const char* decode_simple(
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const char* p,
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uint32_t* a,
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uint32_t* b,
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uint32_t* c,
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uint32_t* d) {
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size_t k = loadUnaligned<uint8_t>(p);
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const char* end = p + detail::groupVarintLengths[k];
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++p;
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size_t k0 = b0key(k);
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*a = loadUnaligned<uint32_t>(p) & kMask[k0];
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p += k0 + 1;
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size_t k1 = b1key(k);
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*b = loadUnaligned<uint32_t>(p) & kMask[k1];
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p += k1 + 1;
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size_t k2 = b2key(k);
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*c = loadUnaligned<uint32_t>(p) & kMask[k2];
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p += k2 + 1;
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size_t k3 = b3key(k);
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*d = loadUnaligned<uint32_t>(p) & kMask[k3];
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// p += k3+1;
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return end;
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}
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/**
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* Decode four uint32_t values from a buffer and store them in the array
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* pointed-to by dest, similar to decode(p,a,b,c,d) above.
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*/
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static const char* decode_simple(const char* p, uint32_t* dest) {
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return decode_simple(p, dest, dest + 1, dest + 2, dest + 3);
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}
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#if FOLLY_SSE >= 3
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/**
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* Just like the non-SSSE3 decode below, but with the additional constraint
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* that we must be able to read at least 17 bytes from the input pointer, p.
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*/
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static const char* decode(const char* p, uint32_t* dest) {
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uint8_t key = uint8_t(p[0]);
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__m128i val = _mm_loadu_si128((const __m128i*)(p + 1));
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__m128i mask =
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_mm_load_si128((const __m128i*)detail::groupVarintSSEMasks[key].data());
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__m128i r = _mm_shuffle_epi8(val, mask);
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_mm_storeu_si128((__m128i*)dest, r);
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return p + detail::groupVarintLengths[key];
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}
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/**
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* Just like decode_simple, but with the additional constraint that
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* we must be able to read at least 17 bytes from the input pointer, p.
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*/
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static const char*
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decode(const char* p, uint32_t* a, uint32_t* b, uint32_t* c, uint32_t* d) {
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uint8_t key = uint8_t(p[0]);
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__m128i val = _mm_loadu_si128((const __m128i*)(p + 1));
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__m128i mask =
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_mm_load_si128((const __m128i*)detail::groupVarintSSEMasks[key].data());
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__m128i r = _mm_shuffle_epi8(val, mask);
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// Extracting 32 bits at a time out of an XMM register is a SSE4 feature
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#if FOLLY_SSE >= 4
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*a = uint32_t(_mm_extract_epi32(r, 0));
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*b = uint32_t(_mm_extract_epi32(r, 1));
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*c = uint32_t(_mm_extract_epi32(r, 2));
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*d = uint32_t(_mm_extract_epi32(r, 3));
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#else /* !__SSE4__ */
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*a = _mm_extract_epi16(r, 0) + (_mm_extract_epi16(r, 1) << 16);
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*b = _mm_extract_epi16(r, 2) + (_mm_extract_epi16(r, 3) << 16);
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*c = _mm_extract_epi16(r, 4) + (_mm_extract_epi16(r, 5) << 16);
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*d = _mm_extract_epi16(r, 6) + (_mm_extract_epi16(r, 7) << 16);
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#endif /* __SSE4__ */
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return p + detail::groupVarintLengths[key];
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}
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#else /* !__SSSE3__ */
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static const char*
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decode(const char* p, uint32_t* a, uint32_t* b, uint32_t* c, uint32_t* d) {
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return decode_simple(p, a, b, c, d);
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}
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static const char* decode(const char* p, uint32_t* dest) {
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return decode_simple(p, dest);
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}
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#endif /* __SSSE3__ */
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private:
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static uint8_t key(uint32_t x) {
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// __builtin_clz is undefined for the x==0 case
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return uint8_t(3 - (__builtin_clz(x | 1) / 8));
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}
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static size_t b0key(size_t x) {
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return x & 3;
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}
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static size_t b1key(size_t x) {
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return (x >> 2) & 3;
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}
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static size_t b2key(size_t x) {
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return (x >> 4) & 3;
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}
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static size_t b3key(size_t x) {
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return (x >> 6) & 3;
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}
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static const uint32_t kMask[];
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};
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/**
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* GroupVarint encoding for 64-bit values.
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*
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* Encodes 5 64-bit integers at once, each using 1-8 bytes depending on size.
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* There are two bytes of overhead. (The first two bytes contain the lengths
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* of the five integers encoded as three bits each; 000=1 byte .. 111 = 8 bytes)
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*
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* This implementation assumes little-endian and does unaligned 64-bit
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* accesses, so it's basically not portable outside of the x86[_64] world.
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*/
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template <>
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class GroupVarint<uint64_t> : public detail::GroupVarintBase<uint64_t> {
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public:
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/**
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* Return the number of bytes used to encode these five values.
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*/
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static size_t
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size(uint64_t a, uint64_t b, uint64_t c, uint64_t d, uint64_t e) {
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return kHeaderSize + kGroupSize + key(a) + key(b) + key(c) + key(d) +
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key(e);
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}
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/**
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* Return the number of bytes used to encode five uint64_t values stored
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* at consecutive positions in an array.
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*/
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static size_t size(const uint64_t* p) {
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return size(p[0], p[1], p[2], p[3], p[4]);
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}
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/**
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* Return the number of bytes used to encode count (<= 4) values.
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* If you clip a buffer after these many bytes, you can still decode
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* the first "count" values correctly (if the remaining size() -
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* partialSize() bytes are filled with garbage).
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*/
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static size_t partialSize(const type* p, size_t count) {
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DCHECK_LE(count, kGroupSize);
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size_t s = kHeaderSize + count;
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for (; count; --count, ++p) {
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s += key(*p);
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}
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return s;
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}
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/**
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* Return the number of values from *p that are valid from an encoded
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* buffer of size bytes.
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*/
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static size_t partialCount(const char* p, size_t size) {
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uint16_t v = loadUnaligned<uint16_t>(p);
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size_t s = kHeaderSize;
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s += 1 + b0key(v);
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if (s > size) {
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return 0;
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}
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s += 1 + b1key(v);
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if (s > size) {
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return 1;
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}
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s += 1 + b2key(v);
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if (s > size) {
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return 2;
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}
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s += 1 + b3key(v);
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if (s > size) {
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return 3;
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}
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s += 1 + b4key(v);
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if (s > size) {
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return 4;
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}
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return 5;
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}
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/**
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* Given a pointer to the beginning of an GroupVarint64-encoded block,
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* return the number of bytes used by the encoding.
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*/
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static size_t encodedSize(const char* p) {
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uint16_t n = loadUnaligned<uint16_t>(p);
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return kHeaderSize + kGroupSize + b0key(n) + b1key(n) + b2key(n) +
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b3key(n) + b4key(n);
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}
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/**
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* Encode five uint64_t values into the buffer pointed-to by p, and return
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* the next position in the buffer (that is, one character past the last
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* encoded byte). p needs to have at least size()+8 bytes available.
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*/
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static char*
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encode(char* p, uint64_t a, uint64_t b, uint64_t c, uint64_t d, uint64_t e) {
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uint16_t b0key = key(a);
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uint16_t b1key = key(b);
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uint16_t b2key = key(c);
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uint16_t b3key = key(d);
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uint16_t b4key = key(e);
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storeUnaligned<uint16_t>(
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p,
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uint16_t(
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(b4key << 12) | (b3key << 9) | (b2key << 6) | (b1key << 3) |
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b0key));
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p += 2;
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storeUnaligned(p, a);
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p += b0key + 1;
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storeUnaligned(p, b);
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p += b1key + 1;
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storeUnaligned(p, c);
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p += b2key + 1;
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storeUnaligned(p, d);
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p += b3key + 1;
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storeUnaligned(p, e);
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p += b4key + 1;
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return p;
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}
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/**
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* Encode five uint64_t values from the array pointed-to by src into the
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* buffer pointed-to by p, similar to encode(p,a,b,c,d,e) above.
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*/
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static char* encode(char* p, const uint64_t* src) {
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return encode(p, src[0], src[1], src[2], src[3], src[4]);
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}
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/**
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* Decode five uint64_t values from a buffer, and return the next position
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* in the buffer (that is, one character past the last encoded byte).
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* The buffer needs to have at least 7 bytes available (they may be read
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* but ignored).
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*/
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static const char* decode(
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const char* p,
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uint64_t* a,
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uint64_t* b,
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uint64_t* c,
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uint64_t* d,
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uint64_t* e) {
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uint16_t k = loadUnaligned<uint16_t>(p);
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p += 2;
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uint8_t k0 = b0key(k);
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*a = loadUnaligned<uint64_t>(p) & kMask[k0];
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p += k0 + 1;
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uint8_t k1 = b1key(k);
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*b = loadUnaligned<uint64_t>(p) & kMask[k1];
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p += k1 + 1;
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uint8_t k2 = b2key(k);
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*c = loadUnaligned<uint64_t>(p) & kMask[k2];
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p += k2 + 1;
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uint8_t k3 = b3key(k);
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*d = loadUnaligned<uint64_t>(p) & kMask[k3];
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p += k3 + 1;
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uint8_t k4 = b4key(k);
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*e = loadUnaligned<uint64_t>(p) & kMask[k4];
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p += k4 + 1;
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return p;
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}
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/**
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* Decode five uint64_t values from a buffer and store them in the array
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* pointed-to by dest, similar to decode(p,a,b,c,d,e) above.
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*/
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static const char* decode(const char* p, uint64_t* dest) {
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return decode(p, dest, dest + 1, dest + 2, dest + 3, dest + 4);
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}
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private:
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enum { kHeaderBytes = 2 };
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static uint8_t key(uint64_t x) {
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// __builtin_clzll is undefined for the x==0 case
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return uint8_t(7 - (__builtin_clzll(x | 1) / 8));
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}
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static uint8_t b0key(uint16_t x) {
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return x & 7u;
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}
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static uint8_t b1key(uint16_t x) {
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return (x >> 3) & 7u;
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}
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static uint8_t b2key(uint16_t x) {
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return (x >> 6) & 7u;
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}
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static uint8_t b3key(uint16_t x) {
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return (x >> 9) & 7u;
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}
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static uint8_t b4key(uint16_t x) {
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return (x >> 12) & 7u;
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}
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static const uint64_t kMask[];
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};
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typedef GroupVarint<uint32_t> GroupVarint32;
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typedef GroupVarint<uint64_t> GroupVarint64;
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/**
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* Simplify use of GroupVarint* for the case where data is available one
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* entry at a time (instead of one group at a time). Handles buffering
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* and an incomplete last chunk.
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*
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|
* Output is a function object that accepts character ranges:
|
|
* out(StringPiece) appends the given character range to the output.
|
|
*/
|
|
template <class T, class Output>
|
|
class GroupVarintEncoder {
|
|
public:
|
|
typedef GroupVarint<T> Base;
|
|
typedef T type;
|
|
|
|
explicit GroupVarintEncoder(Output out) : out_(out), count_(0) {}
|
|
|
|
~GroupVarintEncoder() {
|
|
finish();
|
|
}
|
|
|
|
/**
|
|
* Add a value to the encoder.
|
|
*/
|
|
void add(type val) {
|
|
buf_[count_++] = val;
|
|
if (count_ == Base::kGroupSize) {
|
|
char* p = Base::encode(tmp_, buf_);
|
|
out_(StringPiece(tmp_, p));
|
|
count_ = 0;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Finish encoding, flushing any buffered values if necessary.
|
|
* After finish(), the encoder is immediately ready to encode more data
|
|
* to the same output.
|
|
*/
|
|
void finish() {
|
|
if (count_) {
|
|
// This is not strictly necessary, but it makes testing easy;
|
|
// uninitialized bytes are guaranteed to be recorded as taking one byte
|
|
// (not more).
|
|
for (size_t i = count_; i < Base::kGroupSize; i++) {
|
|
buf_[i] = 0;
|
|
}
|
|
Base::encode(tmp_, buf_);
|
|
out_(StringPiece(tmp_, Base::partialSize(buf_, count_)));
|
|
count_ = 0;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Return the appender that was used.
|
|
*/
|
|
Output& output() {
|
|
return out_;
|
|
}
|
|
const Output& output() const {
|
|
return out_;
|
|
}
|
|
|
|
/**
|
|
* Reset the encoder, disregarding any state (except what was already
|
|
* flushed to the output, of course).
|
|
*/
|
|
void clear() {
|
|
count_ = 0;
|
|
}
|
|
|
|
private:
|
|
Output out_;
|
|
char tmp_[Base::kMaxSize];
|
|
type buf_[Base::kGroupSize];
|
|
size_t count_;
|
|
};
|
|
|
|
/**
|
|
* Simplify use of GroupVarint* for the case where the last group in the
|
|
* input may be incomplete (but the exact size of the input is known).
|
|
* Allows for extracting values one at a time.
|
|
*/
|
|
template <typename T>
|
|
class GroupVarintDecoder {
|
|
public:
|
|
typedef GroupVarint<T> Base;
|
|
typedef T type;
|
|
|
|
GroupVarintDecoder() = default;
|
|
|
|
explicit GroupVarintDecoder(StringPiece data, size_t maxCount = (size_t)-1)
|
|
: rrest_(data.end()),
|
|
p_(data.data()),
|
|
end_(data.end()),
|
|
limit_(end_),
|
|
pos_(0),
|
|
count_(0),
|
|
remaining_(maxCount) {}
|
|
|
|
void reset(StringPiece data, size_t maxCount = (size_t)-1) {
|
|
rrest_ = data.end();
|
|
p_ = data.data();
|
|
end_ = data.end();
|
|
limit_ = end_;
|
|
pos_ = 0;
|
|
count_ = 0;
|
|
remaining_ = maxCount;
|
|
}
|
|
|
|
/**
|
|
* Read and return the next value.
|
|
*/
|
|
bool next(type* val) {
|
|
if (pos_ == count_) {
|
|
// refill
|
|
size_t rem = size_t(end_ - p_);
|
|
if (rem == 0 || remaining_ == 0) {
|
|
return false;
|
|
}
|
|
// next() attempts to read one full group at a time, and so we must have
|
|
// at least enough bytes readable after its end to handle the case if the
|
|
// last group is full.
|
|
//
|
|
// The best way to ensure this is to ensure that data has at least
|
|
// Base::kMaxSize - 1 bytes readable *after* the end, otherwise we'll copy
|
|
// into a temporary buffer.
|
|
if (limit_ - p_ < Base::kMaxSize) {
|
|
memcpy(tmp_, p_, rem);
|
|
p_ = tmp_;
|
|
end_ = p_ + rem;
|
|
limit_ = tmp_ + sizeof(tmp_);
|
|
}
|
|
pos_ = 0;
|
|
const char* n = Base::decode(p_, buf_);
|
|
if (n <= end_) {
|
|
// Full group could be decoded
|
|
if (remaining_ >= Base::kGroupSize) {
|
|
remaining_ -= Base::kGroupSize;
|
|
count_ = Base::kGroupSize;
|
|
p_ = n;
|
|
} else {
|
|
count_ = remaining_;
|
|
remaining_ = 0;
|
|
p_ += Base::partialSize(buf_, count_);
|
|
}
|
|
} else {
|
|
// Can't decode a full group
|
|
count_ = Base::partialCount(p_, size_t(end_ - p_));
|
|
if (remaining_ >= count_) {
|
|
remaining_ -= count_;
|
|
p_ = end_;
|
|
} else {
|
|
count_ = remaining_;
|
|
remaining_ = 0;
|
|
p_ += Base::partialSize(buf_, count_);
|
|
}
|
|
if (count_ == 0) {
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
*val = buf_[pos_++];
|
|
return true;
|
|
}
|
|
|
|
StringPiece rest() const {
|
|
// This is only valid after next() returned false
|
|
CHECK(pos_ == count_ && (p_ == end_ || remaining_ == 0));
|
|
// p_ may point to the internal buffer (tmp_), but we want
|
|
// to return subpiece of the original data
|
|
size_t size = size_t(end_ - p_);
|
|
return StringPiece(rrest_ - size, rrest_);
|
|
}
|
|
|
|
private:
|
|
const char* rrest_;
|
|
const char* p_;
|
|
const char* end_;
|
|
const char* limit_;
|
|
char tmp_[2 * Base::kMaxSize];
|
|
type buf_[Base::kGroupSize];
|
|
size_t pos_;
|
|
size_t count_;
|
|
size_t remaining_;
|
|
};
|
|
|
|
typedef GroupVarintDecoder<uint32_t> GroupVarint32Decoder;
|
|
typedef GroupVarintDecoder<uint64_t> GroupVarint64Decoder;
|
|
|
|
} // namespace folly
|
|
|
|
#endif /* FOLLY_X64 || defined(__i386__) || FOLLY_PPC64 */
|