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@ -3,6 +3,7 @@ |
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package roaring |
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import ( |
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"encoding/binary" |
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"errors" |
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"io" |
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"reflect" |
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@ -132,3 +133,284 @@ func byteSliceAsInterval16Slice(slice []byte) (result []interval16) { |
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// return result
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return |
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} |
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// FromBuffer creates a bitmap from its serialized version stored in buffer.
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// It uses CRoaring's frozen bitmap format.
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//
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// The format specification is available here:
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// https://github.com/RoaringBitmap/CRoaring/blob/2c867e9f9c9e2a3a7032791f94c4c7ae3013f6e0/src/roaring.c#L2756-L2783
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//
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// The provided byte array (buf) is expected to be a constant.
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// The function makes the best effort attempt not to copy data.
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// Only little endian is supported. The function will err if it detects a big
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// endian serialized file.
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// You should take care not to modify buff as it will likely result in
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// unexpected program behavior.
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// If said buffer comes from a memory map, it's advisable to give it read
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// only permissions, either at creation or by calling Mprotect from the
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// golang.org/x/sys/unix package.
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//
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// Resulting bitmaps are effectively immutable in the following sense:
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// a copy-on-write marker is used so that when you modify the resulting
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// bitmap, copies of selected data (containers) are made.
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// You should *not* change the copy-on-write status of the resulting
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// bitmaps (SetCopyOnWrite).
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//
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// If buf becomes unavailable, then a bitmap created with
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// FromBuffer would be effectively broken. Furthermore, any
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// bitmap derived from this bitmap (e.g., via Or, And) might
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// also be broken. Thus, before making buf unavailable, you should
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// call CloneCopyOnWriteContainers on all such bitmaps.
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//
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func (rb *Bitmap) FrozenView(buf []byte) error { |
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return rb.highlowcontainer.frozenView(buf) |
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} |
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/* Verbatim specification from CRoaring. |
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* |
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* FROZEN SERIALIZATION FORMAT DESCRIPTION |
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* |
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* -- (beginning must be aligned by 32 bytes) -- |
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* <bitset_data> uint64_t[BITSET_CONTAINER_SIZE_IN_WORDS * num_bitset_containers] |
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* <run_data> rle16_t[total number of rle elements in all run containers] |
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* <array_data> uint16_t[total number of array elements in all array containers] |
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* <keys> uint16_t[num_containers] |
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* <counts> uint16_t[num_containers] |
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* <typecodes> uint8_t[num_containers] |
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* <header> uint32_t |
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* |
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* <header> is a 4-byte value which is a bit union of FROZEN_COOKIE (15 bits) |
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* and the number of containers (17 bits). |
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* |
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* <counts> stores number of elements for every container. |
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* Its meaning depends on container type. |
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* For array and bitset containers, this value is the container cardinality minus one. |
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* For run container, it is the number of rle_t elements (n_runs). |
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* |
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* <bitset_data>,<array_data>,<run_data> are flat arrays of elements of |
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* all containers of respective type. |
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* |
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* <*_data> and <keys> are kept close together because they are not accessed |
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* during deserilization. This may reduce IO in case of large mmaped bitmaps. |
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* All members have their native alignments during deserilization except <header>, |
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* which is not guaranteed to be aligned by 4 bytes. |
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*/ |
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const FROZEN_COOKIE = 13766 |
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var ( |
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FrozenBitmapInvalidCookie = errors.New("header does not contain the FROZEN_COOKIE") |
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FrozenBitmapBigEndian = errors.New("loading big endian frozen bitmaps is not supported") |
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FrozenBitmapIncomplete = errors.New("input buffer too small to contain a frozen bitmap") |
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FrozenBitmapOverpopulated = errors.New("too many containers") |
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FrozenBitmapUnexpectedData = errors.New("spurious data in input") |
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FrozenBitmapInvalidTypecode = errors.New("unrecognized typecode") |
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FrozenBitmapBufferTooSmall = errors.New("buffer too small") |
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) |
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func (ra *roaringArray) frozenView(buf []byte) error { |
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if len(buf) < 4 { |
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return FrozenBitmapIncomplete |
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} |
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headerBE := binary.BigEndian.Uint32(buf[len(buf)-4:]) |
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if headerBE & 0x7fff == FROZEN_COOKIE { |
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return FrozenBitmapBigEndian |
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} |
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header := binary.LittleEndian.Uint32(buf[len(buf)-4:]) |
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buf = buf[:len(buf)-4] |
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if header & 0x7fff != FROZEN_COOKIE { |
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return FrozenBitmapInvalidCookie |
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} |
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nCont := int(header >> 15) |
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if nCont > (1 << 16) { |
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return FrozenBitmapOverpopulated |
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} |
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// 1 byte per type, 2 bytes per key, 2 bytes per count.
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if len(buf) < 5*nCont { |
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return FrozenBitmapIncomplete |
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} |
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types := buf[len(buf)-nCont:] |
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buf = buf[:len(buf)-nCont] |
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counts := byteSliceAsUint16Slice(buf[len(buf)-2*nCont:]) |
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buf = buf[:len(buf)-2*nCont] |
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keys := byteSliceAsUint16Slice(buf[len(buf)-2*nCont:]) |
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buf = buf[:len(buf)-2*nCont] |
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nBitmap, nArray, nRun := uint64(0), uint64(0), uint64(0) |
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nArrayEl, nRunEl := uint64(0), uint64(0) |
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for i, t := range types { |
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switch (t) { |
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case 1: |
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nBitmap++ |
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case 2: |
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nArray++ |
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nArrayEl += uint64(counts[i])+1 |
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case 3: |
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nRun++ |
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nRunEl += uint64(counts[i]) |
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default: |
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return FrozenBitmapInvalidTypecode |
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} |
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} |
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if uint64(len(buf)) < (1 << 13)*nBitmap + 4*nRunEl + 2*nArrayEl { |
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return FrozenBitmapIncomplete |
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} |
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bitsetsArena := byteSliceAsUint64Slice(buf[:(1 << 13)*nBitmap]) |
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buf = buf[(1 << 13)*nBitmap:] |
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runsArena := byteSliceAsInterval16Slice(buf[:4*nRunEl]) |
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buf = buf[4*nRunEl:] |
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arraysArena := byteSliceAsUint16Slice(buf[:2*nArrayEl]) |
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buf = buf[2*nArrayEl:] |
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if len(buf) != 0 { |
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return FrozenBitmapUnexpectedData |
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} |
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// TODO: maybe arena_alloc all this.
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containers := make([]container, nCont) |
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bitsets := make([]bitmapContainer, nBitmap) |
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arrays := make([]arrayContainer, nArray) |
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runs := make([]runContainer16, nRun) |
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needCOW := make([]bool, nCont) |
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iBitset, iArray, iRun := uint64(0), uint64(0), uint64(0) |
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for i, t := range types { |
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needCOW[i] = true |
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switch (t) { |
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case 1: |
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containers[i] = &bitsets[iBitset] |
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bitsets[iBitset].cardinality = int(counts[i])+1 |
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bitsets[iBitset].bitmap = bitsetsArena[:1024] |
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bitsetsArena = bitsetsArena[1024:] |
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iBitset++ |
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case 2: |
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containers[i] = &arrays[iArray] |
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arrays[iArray].content = arraysArena[:counts[i]+1] |
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arraysArena = arraysArena[counts[i]+1:] |
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iArray++ |
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case 3: |
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containers[i] = &runs[iRun] |
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runs[iRun].iv = runsArena[:counts[i]] |
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runsArena = runsArena[counts[i]:] |
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iRun++ |
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} |
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} |
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// Not consuming the full input is a bug.
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if iBitset != nBitmap || len(bitsetsArena) != 0 || |
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iArray != nArray || len(arraysArena) != 0 || |
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iRun != nRun || len(runsArena) != 0 { |
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panic("we missed something") |
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} |
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ra.keys = keys |
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ra.containers = containers |
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ra.needCopyOnWrite = needCOW |
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ra.copyOnWrite = true |
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return nil |
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} |
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func (bm *Bitmap) GetFrozenSizeInBytes() uint64 { |
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nBits, nArrayEl, nRunEl := uint64(0), uint64(0), uint64(0) |
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for _, c := range bm.highlowcontainer.containers { |
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switch v := c.(type) { |
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case *bitmapContainer: |
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nBits++ |
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case *arrayContainer: |
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nArrayEl += uint64(len(v.content)) |
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case *runContainer16: |
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nRunEl += uint64(len(v.iv)) |
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} |
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} |
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return 4 + 5*uint64(len(bm.highlowcontainer.containers)) + |
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(nBits << 13) + 2*nArrayEl + 4*nRunEl |
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} |
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func (bm *Bitmap) Freeze() ([]byte, error) { |
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sz := bm.GetFrozenSizeInBytes() |
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buf := make([]byte, sz) |
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_, err := bm.FreezeTo(buf) |
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return buf, err |
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} |
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func (bm *Bitmap) FreezeTo(buf []byte) (int, error) { |
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containers := bm.highlowcontainer.containers |
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nCont := len(containers) |
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nBits, nArrayEl, nRunEl := 0, 0, 0 |
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for _, c := range containers { |
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switch v := c.(type) { |
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case *bitmapContainer: |
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nBits++ |
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case *arrayContainer: |
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nArrayEl += len(v.content) |
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case *runContainer16: |
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nRunEl += len(v.iv) |
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} |
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} |
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serialSize := 4 + 5*nCont + (1 << 13)*nBits + 4*nRunEl + 2*nArrayEl |
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if len(buf) < serialSize { |
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return 0, FrozenBitmapBufferTooSmall |
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} |
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bitsArena := byteSliceAsUint64Slice(buf[:(1 << 13)*nBits]) |
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buf = buf[(1 << 13)*nBits:] |
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runsArena := byteSliceAsInterval16Slice(buf[:4*nRunEl]) |
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buf = buf[4*nRunEl:] |
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arraysArena := byteSliceAsUint16Slice(buf[:2*nArrayEl]) |
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buf = buf[2*nArrayEl:] |
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keys := byteSliceAsUint16Slice(buf[:2*nCont]) |
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buf = buf[2*nCont:] |
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counts := byteSliceAsUint16Slice(buf[:2*nCont]) |
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buf = buf[2*nCont:] |
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types := buf[:nCont] |
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buf = buf[nCont:] |
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header := uint32(FROZEN_COOKIE|(nCont << 15)) |
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binary.LittleEndian.PutUint32(buf[:4], header) |
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copy(keys, bm.highlowcontainer.keys[:]) |
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for i, c := range containers { |
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switch v := c.(type) { |
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case *bitmapContainer: |
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copy(bitsArena, v.bitmap) |
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bitsArena = bitsArena[1024:] |
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counts[i] = uint16(v.cardinality-1) |
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types[i] = 1 |
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case *arrayContainer: |
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copy(arraysArena, v.content) |
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arraysArena = arraysArena[len(v.content):] |
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elems := len(v.content) |
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counts[i] = uint16(elems)-1 |
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types[i] = 2 |
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case *runContainer16: |
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copy(runsArena, v.iv) |
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runs := len(v.iv) |
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runsArena = runsArena[runs:] |
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counts[i] = uint16(runs) |
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types[i] = 3 |
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} |
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} |
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return serialSize, nil |
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} |
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techknowlogick
3 years ago
committed by
GitHub