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228 lines
12 KiB
C
228 lines
12 KiB
C
/*
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* the API for FSST compression -- (c) Peter Boncz, Viktor Leis and Thomas Neumann (CWI, TU Munich), 2018-2019
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*
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* ===================================================================================================================================
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* this software is distributed under the MIT License (http://www.opensource.org/licenses/MIT):
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*
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* Copyright 2018-2020, CWI, TU Munich, FSU Jena
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files
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* (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* - The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
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* IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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* You can contact the authors via the FSST source repository : https://github.com/cwida/fsst
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* ===================================================================================================================================
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*
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* FSST: Fast Static Symbol Table compression
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* see the paper https://github.com/cwida/fsst/raw/master/fsstcompression.pdf
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*
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* FSST is a compression scheme focused on string/text data: it can compress strings from distributions with many different values (i.e.
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* where dictionary compression will not work well). It allows *random-access* to compressed data: it is not block-based, so individual
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* strings can be decompressed without touching the surrounding data in a compressed block. When compared to e.g. lz4 (which is
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* block-based), FSST achieves similar decompression speed, (2x) better compression speed and 30% better compression ratio on text.
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*
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* FSST encodes strings also using a symbol table -- but it works on pieces of the string, as it maps "symbols" (1-8 byte sequences)
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* onto "codes" (single-bytes). FSST can also represent a byte as an exception (255 followed by the original byte). Hence, compression
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* transforms a sequence of bytes into a (supposedly shorter) sequence of codes or escaped bytes. These shorter byte-sequences could
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* be seen as strings again and fit in whatever your program is that manipulates strings.
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*
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* useful property: FSST ensures that strings that are equal, are also equal in their compressed form.
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*
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* In this API, strings are considered byte-arrays (byte = unsigned char) and a batch of strings is represented as an array of
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* unsigned char* pointers to their starts. A seperate length array (of unsigned int) denotes how many bytes each string consists of.
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*
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* This representation as unsigned char* pointers tries to assume as little as possible on the memory management of the program
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* that calls this API, and is also intended to allow passing strings into this API without copying (even if you use C++ strings).
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*
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* We optionally support C-style zero-terminated strings (zero appearing only at the end). In this case, the compressed strings are
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* also zero-terminated strings. In zero-terminated mode, the zero-byte at the end *is* counted in the string byte-length.
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*/
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#ifndef FSST_INCLUDED_H
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#define FSST_INCLUDED_H
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#ifdef _MSC_VER
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#define __restrict__
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#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
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#define __ORDER_LITTLE_ENDIAN__ 2
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#include <intrin.h>
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static inline int __builtin_ctzl(unsigned long long x) {
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unsigned long ret;
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_BitScanForward64(&ret, x);
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return (int)ret;
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}
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#endif
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#ifdef __cplusplus
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#define FSST_FALLTHROUGH [[fallthrough]]
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#include <cstring>
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extern "C" {
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#else
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#define FSST_FALLTHROUGH
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#endif
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#include <stddef.h>
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/* A compressed string is simply a string of 1-byte codes; except for code 255, which is followed by an uncompressed byte. */
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#define FSST_ESC 255
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/* Data structure needed for compressing strings - use fsst_duplicate() to create thread-local copies. Use fsst_destroy() to free. */
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typedef void* fsst_encoder_t; /* opaque type - it wraps around a rather large (~900KB) C++ object */
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/* Data structure needed for decompressing strings - read-only and thus can be shared between multiple decompressing threads. */
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typedef struct {
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unsigned long long version; /* version id */
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unsigned char zeroTerminated; /* terminator is a single-byte code that does not appear in longer symbols */
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unsigned char len[255]; /* len[x] is the byte-length of the symbol x (1 < len[x] <= 8). */
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unsigned long long symbol[255]; /* symbol[x] contains in LITTLE_ENDIAN the bytesequence that code x represents (0 <= x < 255). */
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} fsst_decoder_t;
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/* Calibrate a FSST symboltable from a batch of strings (it is best to provide at least 16KB of data). */
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fsst_encoder_t*
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fsst_create(
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size_t n, /* IN: number of strings in batch to sample from. */
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const size_t lenIn[], /* IN: byte-lengths of the inputs */
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const unsigned char *strIn[], /* IN: string start pointers. */
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int zeroTerminated /* IN: whether input strings are zero-terminated. If so, encoded strings are as well (i.e. symbol[0]=""). */
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);
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/* Create another encoder instance, necessary to do multi-threaded encoding using the same symbol table. */
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fsst_encoder_t*
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fsst_duplicate(
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fsst_encoder_t *encoder /* IN: the symbol table to duplicate. */
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);
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#define FSST_MAXHEADER (8+1+8+2048+1) /* maxlen of deserialized fsst header, produced/consumed by fsst_export() resp. fsst_import() */
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/* Space-efficient symbol table serialization (smaller than sizeof(fsst_decoder_t) - by saving on the unused bytes in symbols of len < 8). */
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unsigned int /* OUT: number of bytes written in buf, at most sizeof(fsst_decoder_t) */
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fsst_export(
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fsst_encoder_t *encoder, /* IN: the symbol table to dump. */
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unsigned char *buf /* OUT: pointer to a byte-buffer where to serialize this symbol table. */
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);
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/* Deallocate encoder. */
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void
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fsst_destroy(fsst_encoder_t*);
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/* Return a decoder structure from serialized format (typically used in a block-, file- or row-group header). */
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unsigned int /* OUT: number of bytes consumed in buf (0 on failure). */
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fsst_import(
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fsst_decoder_t *decoder, /* IN: this symbol table will be overwritten. */
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unsigned char const *buf /* IN: pointer to a byte-buffer where fsst_export() serialized this symbol table. */
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);
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/* Return a decoder structure from an encoder. */
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fsst_decoder_t
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fsst_decoder(
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fsst_encoder_t *encoder
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);
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/* Compress a batch of strings (on AVX512 machines best performance is obtained by compressing more than 32KB of string volume). */
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/* The output buffer must be large; at least "conservative space" (7+2*inputlength) for the first string for something to happen. */
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size_t /* OUT: the number of compressed strings (<=n) that fit the output buffer. */
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fsst_compress(
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fsst_encoder_t *encoder, /* IN: encoder obtained from fsst_create(). */
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size_t nstrings, /* IN: number of strings in batch to compress. */
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const size_t lenIn[], /* IN: byte-lengths of the inputs */
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const unsigned char *strIn[], /* IN: input string start pointers. */
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size_t outsize, /* IN: byte-length of output buffer. */
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unsigned char *output, /* OUT: memory buffer to put the compressed strings in (one after the other). */
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size_t lenOut[], /* OUT: byte-lengths of the compressed strings. */
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unsigned char *strOut[] /* OUT: output string start pointers. Will all point into [output,output+size). */
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);
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/* Decompress a single string, inlined for speed. */
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inline size_t /* OUT: bytesize of the decompressed string. If > size, the decoded output is truncated to size. */
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fsst_decompress(
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const fsst_decoder_t *decoder, /* IN: use this symbol table for compression. */
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size_t lenIn, /* IN: byte-length of compressed string. */
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const unsigned char *strIn, /* IN: compressed string. */
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size_t size, /* IN: byte-length of output buffer. */
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unsigned char *output /* OUT: memory buffer to put the decompressed string in. */
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) {
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unsigned char*__restrict__ len = (unsigned char* __restrict__) decoder->len;
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unsigned char*__restrict__ strOut = (unsigned char* __restrict__) output;
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unsigned long long*__restrict__ symbol = (unsigned long long* __restrict__) decoder->symbol;
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size_t code, posOut = 0, posIn = 0;
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#ifndef FSST_MUST_ALIGN /* defining on platforms that require aligned memory access may help their performance */
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#define FSST_UNALIGNED_STORE(dst,src) memcpy((unsigned long long*) (dst), &(src), sizeof(unsigned long long))
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#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
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while (posOut+32 <= size && posIn+4 <= lenIn) {
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unsigned int nextBlock, escapeMask;
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memcpy(&nextBlock, strIn+posIn, sizeof(unsigned int));
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escapeMask = (nextBlock&0x80808080u)&((((~nextBlock)&0x7F7F7F7Fu)+0x7F7F7F7Fu)^0x80808080u);
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if (escapeMask == 0) {
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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} else {
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unsigned long firstEscapePos=__builtin_ctzl((unsigned long long) escapeMask)>>3;
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switch(firstEscapePos) { /* Duff's device */
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case 3: code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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// fall through
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case 2: code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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// fall through
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case 1: code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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// fall through
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case 0: posIn+=2; strOut[posOut++] = strIn[posIn-1]; /* decompress an escaped byte */
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}
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}
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}
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if (posOut+24 <= size) { // handle the possibly 3 last bytes without a loop
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if (posIn+2 <= lenIn) {
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strOut[posOut] = strIn[posIn+1];
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if (strIn[posIn] != FSST_ESC) {
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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if (strIn[posIn] != FSST_ESC) {
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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} else {
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posIn += 2; strOut[posOut++] = strIn[posIn-1];
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}
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} else {
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posIn += 2; posOut++;
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}
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}
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if (posIn < lenIn) { // last code cannot be an escape
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code = strIn[posIn++]; FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); posOut += len[code];
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}
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}
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#else
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while (posOut+8 <= size && posIn < lenIn)
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if ((code = strIn[posIn++]) < FSST_ESC) { /* symbol compressed as code? */
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FSST_UNALIGNED_STORE(strOut+posOut, symbol[code]); /* unaligned memory write */
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posOut += len[code];
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} else {
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strOut[posOut] = strIn[posIn]; /* decompress an escaped byte */
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posIn++; posOut++;
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}
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#endif
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#endif
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while (posIn < lenIn)
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if ((code = strIn[posIn++]) < FSST_ESC) {
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size_t posWrite = posOut, endWrite = posOut + len[code];
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unsigned char* __restrict__ symbolPointer = ((unsigned char* __restrict__) &symbol[code]) - posWrite;
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if ((posOut = endWrite) > size) endWrite = size;
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for(; posWrite < endWrite; posWrite++) /* only write if there is room */
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strOut[posWrite] = symbolPointer[posWrite];
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} else {
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if (posOut < size) strOut[posOut] = strIn[posIn]; /* idem */
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posIn++; posOut++;
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}
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if (posOut >= size && (decoder->zeroTerminated&1)) strOut[size-1] = 0;
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return posOut; /* full size of decompressed string (could be >size, then the actually decompressed part) */
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}
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#ifdef __cplusplus
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}
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#endif
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#endif /* FSST_INCLUDED_H */
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