2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
19 #if !defined(__GNUC__) && !defined(_MSC_VER)
20 #error GroupVarint.h requires GCC or MSVC
23 #include <folly/Portability.h>
25 #if FOLLY_X64 || defined(__i386__) || FOLLY_PPC64 || FOLLY_A64
26 #define HAVE_GROUP_VARINT 1
30 #include <folly/detail/GroupVarintDetail.h>
31 #include <folly/Bits.h>
32 #include <folly/Range.h>
33 #include <folly/portability/Builtins.h>
34 #include <glog/logging.h>
37 #include <nmmintrin.h>
40 alignas(16) extern const uint64_t groupVarintSSEMasks[];
47 extern const uint8_t groupVarintLengths[];
57 * GroupVarint encoding for 32-bit values.
59 * Encodes 4 32-bit integers at once, each using 1-4 bytes depending on size.
60 * There is one byte of overhead. (The first byte contains the lengths of
61 * the four integers encoded as two bits each; 00=1 byte .. 11=4 bytes)
63 * This implementation assumes little-endian and does unaligned 32-bit
64 * accesses, so it's basically not portable outside of the x86[_64] world.
67 class GroupVarint<uint32_t> : public detail::GroupVarintBase<uint32_t> {
71 * Return the number of bytes used to encode these four values.
73 static size_t size(uint32_t a, uint32_t b, uint32_t c, uint32_t d) {
74 return kHeaderSize + kGroupSize + key(a) + key(b) + key(c) + key(d);
78 * Return the number of bytes used to encode four uint32_t values stored
79 * at consecutive positions in an array.
81 static size_t size(const uint32_t* p) {
82 return size(p[0], p[1], p[2], p[3]);
86 * Return the number of bytes used to encode count (<= 4) values.
87 * If you clip a buffer after these many bytes, you can still decode
88 * the first "count" values correctly (if the remaining size() -
89 * partialSize() bytes are filled with garbage).
91 static size_t partialSize(const type* p, size_t count) {
92 DCHECK_LE(count, kGroupSize);
93 size_t s = kHeaderSize + count;
94 for (; count; --count, ++p) {
101 * Return the number of values from *p that are valid from an encoded
102 * buffer of size bytes.
104 static size_t partialCount(const char* p, size_t size) {
105 uint8_t v = uint8_t(*p);
106 size_t s = kHeaderSize;
108 if (s > size) return 0;
110 if (s > size) return 1;
112 if (s > size) return 2;
114 if (s > size) return 3;
119 * Given a pointer to the beginning of an GroupVarint32-encoded block,
120 * return the number of bytes used by the encoding.
122 static size_t encodedSize(const char* p) {
123 return kHeaderSize + kGroupSize +
124 b0key(uint8_t(*p)) + b1key(uint8_t(*p)) +
125 b2key(uint8_t(*p)) + b3key(uint8_t(*p));
129 * Encode four uint32_t values into the buffer pointed-to by p, and return
130 * the next position in the buffer (that is, one character past the last
131 * encoded byte). p needs to have at least size()+4 bytes available.
133 static char* encode(char* p, uint32_t a, uint32_t b, uint32_t c, uint32_t d) {
134 uint8_t b0key = key(a);
135 uint8_t b1key = key(b);
136 uint8_t b2key = key(c);
137 uint8_t b3key = key(d);
138 *p++ = (b3key << 6) | (b2key << 4) | (b1key << 2) | b0key;
139 storeUnaligned(p, a);
141 storeUnaligned(p, b);
143 storeUnaligned(p, c);
145 storeUnaligned(p, d);
151 * Encode four uint32_t values from the array pointed-to by src into the
152 * buffer pointed-to by p, similar to encode(p,a,b,c,d) above.
154 static char* encode(char* p, const uint32_t* src) {
155 return encode(p, src[0], src[1], src[2], src[3]);
159 * Decode four uint32_t values from a buffer, and return the next position
160 * in the buffer (that is, one character past the last encoded byte).
161 * The buffer needs to have at least 3 extra bytes available (they
162 * may be read but ignored).
164 static const char* decode_simple(const char* p, uint32_t* a, uint32_t* b,
165 uint32_t* c, uint32_t* d) {
166 size_t k = loadUnaligned<uint8_t>(p);
167 const char* end = p + detail::groupVarintLengths[k];
169 size_t k0 = b0key(k);
170 *a = loadUnaligned<uint32_t>(p) & kMask[k0];
172 size_t k1 = b1key(k);
173 *b = loadUnaligned<uint32_t>(p) & kMask[k1];
175 size_t k2 = b2key(k);
176 *c = loadUnaligned<uint32_t>(p) & kMask[k2];
178 size_t k3 = b3key(k);
179 *d = loadUnaligned<uint32_t>(p) & kMask[k3];
185 * Decode four uint32_t values from a buffer and store them in the array
186 * pointed-to by dest, similar to decode(p,a,b,c,d) above.
188 static const char* decode_simple(const char* p, uint32_t* dest) {
189 return decode_simple(p, dest, dest+1, dest+2, dest+3);
194 * Just like the non-SSSE3 decode below, but with the additional constraint
195 * that we must be able to read at least 17 bytes from the input pointer, p.
197 static const char* decode(const char* p, uint32_t* dest) {
198 uint8_t key = uint8_t(p[0]);
199 __m128i val = _mm_loadu_si128((const __m128i*)(p+1));
201 _mm_load_si128((const __m128i*)&detail::groupVarintSSEMasks[key * 2]);
202 __m128i r = _mm_shuffle_epi8(val, mask);
203 _mm_storeu_si128((__m128i*)dest, r);
204 return p + detail::groupVarintLengths[key];
208 * Just like decode_simple, but with the additional constraint that
209 * we must be able to read at least 17 bytes from the input pointer, p.
211 static const char* decode(const char* p, uint32_t* a, uint32_t* b,
212 uint32_t* c, uint32_t* d) {
213 uint8_t key = uint8_t(p[0]);
214 __m128i val = _mm_loadu_si128((const __m128i*)(p+1));
216 _mm_load_si128((const __m128i*)&detail::groupVarintSSEMasks[key * 2]);
217 __m128i r = _mm_shuffle_epi8(val, mask);
219 // Extracting 32 bits at a time out of an XMM register is a SSE4 feature
221 *a = uint32_t(_mm_extract_epi32(r, 0));
222 *b = uint32_t(_mm_extract_epi32(r, 1));
223 *c = uint32_t(_mm_extract_epi32(r, 2));
224 *d = uint32_t(_mm_extract_epi32(r, 3));
225 #else /* !__SSE4__ */
226 *a = _mm_extract_epi16(r, 0) + (_mm_extract_epi16(r, 1) << 16);
227 *b = _mm_extract_epi16(r, 2) + (_mm_extract_epi16(r, 3) << 16);
228 *c = _mm_extract_epi16(r, 4) + (_mm_extract_epi16(r, 5) << 16);
229 *d = _mm_extract_epi16(r, 6) + (_mm_extract_epi16(r, 7) << 16);
230 #endif /* __SSE4__ */
232 return p + detail::groupVarintLengths[key];
235 #else /* !__SSSE3__ */
236 static const char* decode(const char* p, uint32_t* a, uint32_t* b,
237 uint32_t* c, uint32_t* d) {
238 return decode_simple(p, a, b, c, d);
241 static const char* decode(const char* p, uint32_t* dest) {
242 return decode_simple(p, dest);
244 #endif /* __SSSE3__ */
247 static uint8_t key(uint32_t x) {
248 // __builtin_clz is undefined for the x==0 case
249 return uint8_t(3 - (__builtin_clz(x | 1) / 8));
251 static size_t b0key(size_t x) { return x & 3; }
252 static size_t b1key(size_t x) { return (x >> 2) & 3; }
253 static size_t b2key(size_t x) { return (x >> 4) & 3; }
254 static size_t b3key(size_t x) { return (x >> 6) & 3; }
256 static const uint32_t kMask[];
261 * GroupVarint encoding for 64-bit values.
263 * Encodes 5 64-bit integers at once, each using 1-8 bytes depending on size.
264 * There are two bytes of overhead. (The first two bytes contain the lengths
265 * of the five integers encoded as three bits each; 000=1 byte .. 111 = 8 bytes)
267 * This implementation assumes little-endian and does unaligned 64-bit
268 * accesses, so it's basically not portable outside of the x86[_64] world.
271 class GroupVarint<uint64_t> : public detail::GroupVarintBase<uint64_t> {
274 * Return the number of bytes used to encode these five values.
276 static size_t size(uint64_t a, uint64_t b, uint64_t c, uint64_t d,
278 return kHeaderSize + kGroupSize +
279 key(a) + key(b) + key(c) + key(d) + key(e);
283 * Return the number of bytes used to encode five uint64_t values stored
284 * at consecutive positions in an array.
286 static size_t size(const uint64_t* p) {
287 return size(p[0], p[1], p[2], p[3], p[4]);
291 * Return the number of bytes used to encode count (<= 4) values.
292 * If you clip a buffer after these many bytes, you can still decode
293 * the first "count" values correctly (if the remaining size() -
294 * partialSize() bytes are filled with garbage).
296 static size_t partialSize(const type* p, size_t count) {
297 DCHECK_LE(count, kGroupSize);
298 size_t s = kHeaderSize + count;
299 for (; count; --count, ++p) {
306 * Return the number of values from *p that are valid from an encoded
307 * buffer of size bytes.
309 static size_t partialCount(const char* p, size_t size) {
310 uint16_t v = loadUnaligned<uint16_t>(p);
311 size_t s = kHeaderSize;
313 if (s > size) return 0;
315 if (s > size) return 1;
317 if (s > size) return 2;
319 if (s > size) return 3;
321 if (s > size) return 4;
326 * Given a pointer to the beginning of an GroupVarint64-encoded block,
327 * return the number of bytes used by the encoding.
329 static size_t encodedSize(const char* p) {
330 uint16_t n = loadUnaligned<uint16_t>(p);
331 return kHeaderSize + kGroupSize +
332 b0key(n) + b1key(n) + b2key(n) + b3key(n) + b4key(n);
336 * Encode five uint64_t values into the buffer pointed-to by p, and return
337 * the next position in the buffer (that is, one character past the last
338 * encoded byte). p needs to have at least size()+8 bytes available.
340 static char* encode(char* p, uint64_t a, uint64_t b, uint64_t c,
341 uint64_t d, uint64_t e) {
342 uint16_t b0key = key(a);
343 uint16_t b1key = key(b);
344 uint16_t b2key = key(c);
345 uint16_t b3key = key(d);
346 uint16_t b4key = key(e);
347 storeUnaligned<uint16_t>(
356 storeUnaligned(p, a);
358 storeUnaligned(p, b);
360 storeUnaligned(p, c);
362 storeUnaligned(p, d);
364 storeUnaligned(p, e);
370 * Encode five uint64_t values from the array pointed-to by src into the
371 * buffer pointed-to by p, similar to encode(p,a,b,c,d,e) above.
373 static char* encode(char* p, const uint64_t* src) {
374 return encode(p, src[0], src[1], src[2], src[3], src[4]);
378 * Decode five uint64_t values from a buffer, and return the next position
379 * in the buffer (that is, one character past the last encoded byte).
380 * The buffer needs to have at least 7 bytes available (they may be read
383 static const char* decode(const char* p, uint64_t* a, uint64_t* b,
384 uint64_t* c, uint64_t* d, uint64_t* e) {
385 uint16_t k = loadUnaligned<uint16_t>(p);
387 uint8_t k0 = b0key(k);
388 *a = loadUnaligned<uint64_t>(p) & kMask[k0];
390 uint8_t k1 = b1key(k);
391 *b = loadUnaligned<uint64_t>(p) & kMask[k1];
393 uint8_t k2 = b2key(k);
394 *c = loadUnaligned<uint64_t>(p) & kMask[k2];
396 uint8_t k3 = b3key(k);
397 *d = loadUnaligned<uint64_t>(p) & kMask[k3];
399 uint8_t k4 = b4key(k);
400 *e = loadUnaligned<uint64_t>(p) & kMask[k4];
406 * Decode five uint64_t values from a buffer and store them in the array
407 * pointed-to by dest, similar to decode(p,a,b,c,d,e) above.
409 static const char* decode(const char* p, uint64_t* dest) {
410 return decode(p, dest, dest+1, dest+2, dest+3, dest+4);
414 enum { kHeaderBytes = 2 };
416 static uint8_t key(uint64_t x) {
417 // __builtin_clzll is undefined for the x==0 case
418 return uint8_t(7 - (__builtin_clzll(x | 1) / 8));
421 static uint8_t b0key(uint16_t x) { return x & 7u; }
422 static uint8_t b1key(uint16_t x) { return (x >> 3) & 7u; }
423 static uint8_t b2key(uint16_t x) { return (x >> 6) & 7u; }
424 static uint8_t b3key(uint16_t x) { return (x >> 9) & 7u; }
425 static uint8_t b4key(uint16_t x) { return (x >> 12) & 7u; }
427 static const uint64_t kMask[];
430 typedef GroupVarint<uint32_t> GroupVarint32;
431 typedef GroupVarint<uint64_t> GroupVarint64;
434 * Simplify use of GroupVarint* for the case where data is available one
435 * entry at a time (instead of one group at a time). Handles buffering
436 * and an incomplete last chunk.
438 * Output is a function object that accepts character ranges:
439 * out(StringPiece) appends the given character range to the output.
441 template <class T, class Output>
442 class GroupVarintEncoder {
444 typedef GroupVarint<T> Base;
447 explicit GroupVarintEncoder(Output out)
452 ~GroupVarintEncoder() {
457 * Add a value to the encoder.
460 buf_[count_++] = val;
461 if (count_ == Base::kGroupSize) {
462 char* p = Base::encode(tmp_, buf_);
463 out_(StringPiece(tmp_, p));
469 * Finish encoding, flushing any buffered values if necessary.
470 * After finish(), the encoder is immediately ready to encode more data
471 * to the same output.
475 // This is not strictly necessary, but it makes testing easy;
476 // uninitialized bytes are guaranteed to be recorded as taking one byte
478 for (size_t i = count_; i < Base::kGroupSize; i++) {
481 Base::encode(tmp_, buf_);
482 out_(StringPiece(tmp_, Base::partialSize(buf_, count_)));
488 * Return the appender that was used.
493 const Output& output() const {
498 * Reset the encoder, disregarding any state (except what was already
499 * flushed to the output, of course).
507 char tmp_[Base::kMaxSize];
508 type buf_[Base::kGroupSize];
513 * Simplify use of GroupVarint* for the case where the last group in the
514 * input may be incomplete (but the exact size of the input is known).
515 * Allows for extracting values one at a time.
517 template <typename T>
518 class GroupVarintDecoder {
520 typedef GroupVarint<T> Base;
523 GroupVarintDecoder() = default;
525 explicit GroupVarintDecoder(StringPiece data,
526 size_t maxCount = (size_t)-1)
527 : rrest_(data.end()),
533 remaining_(maxCount) {
536 void reset(StringPiece data, size_t maxCount = (size_t)-1) {
543 remaining_ = maxCount;
547 * Read and return the next value.
549 bool next(type* val) {
550 if (pos_ == count_) {
552 size_t rem = size_t(end_ - p_);
553 if (rem == 0 || remaining_ == 0) {
556 // next() attempts to read one full group at a time, and so we must have
557 // at least enough bytes readable after its end to handle the case if the
558 // last group is full.
560 // The best way to ensure this is to ensure that data has at least
561 // Base::kMaxSize - 1 bytes readable *after* the end, otherwise we'll copy
562 // into a temporary buffer.
563 if (limit_ - p_ < Base::kMaxSize) {
564 memcpy(tmp_, p_, rem);
567 limit_ = tmp_ + sizeof(tmp_);
570 const char* n = Base::decode(p_, buf_);
572 // Full group could be decoded
573 if (remaining_ >= Base::kGroupSize) {
574 remaining_ -= Base::kGroupSize;
575 count_ = Base::kGroupSize;
580 p_ += Base::partialSize(buf_, count_);
583 // Can't decode a full group
584 count_ = Base::partialCount(p_, size_t(end_ - p_));
585 if (remaining_ >= count_) {
586 remaining_ -= count_;
591 p_ += Base::partialSize(buf_, count_);
602 StringPiece rest() const {
603 // This is only valid after next() returned false
604 CHECK(pos_ == count_ && (p_ == end_ || remaining_ == 0));
605 // p_ may point to the internal buffer (tmp_), but we want
606 // to return subpiece of the original data
607 size_t size = size_t(end_ - p_);
608 return StringPiece(rrest_ - size, rrest_);
616 char tmp_[2 * Base::kMaxSize];
617 type buf_[Base::kGroupSize];
623 typedef GroupVarintDecoder<uint32_t> GroupVarint32Decoder;
624 typedef GroupVarintDecoder<uint64_t> GroupVarint64Decoder;
628 #endif /* FOLLY_X64 || defined(__i386__) || FOLLY_PPC64 */