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Edit File: zdict.h
/* * Copyright (c) Meta Platforms, Inc. and affiliates. * All rights reserved. * * This source code is licensed under both the BSD-style license (found in the * LICENSE file in the root directory of this source tree) and the GPLv2 (found * in the COPYING file in the root directory of this source tree). * You may select, at your option, one of the above-listed licenses. */ #if defined (__cplusplus) extern "C" { #endif #ifndef ZSTD_ZDICT_H #define ZSTD_ZDICT_H /*====== Dependencies ======*/ #include <stddef.h> /* size_t */ /* ===== ZDICTLIB_API : control library symbols visibility ===== */ #ifndef ZDICTLIB_VISIBLE /* Backwards compatibility with old macro name */ # ifdef ZDICTLIB_VISIBILITY # define ZDICTLIB_VISIBLE ZDICTLIB_VISIBILITY # elif defined(__GNUC__) && (__GNUC__ >= 4) && !defined(__MINGW32__) # define ZDICTLIB_VISIBLE __attribute__ ((visibility ("default"))) # else # define ZDICTLIB_VISIBLE # endif #endif #ifndef ZDICTLIB_HIDDEN # if defined(__GNUC__) && (__GNUC__ >= 4) && !defined(__MINGW32__) # define ZDICTLIB_HIDDEN __attribute__ ((visibility ("hidden"))) # else # define ZDICTLIB_HIDDEN # endif #endif #if defined(ZSTD_DLL_EXPORT) && (ZSTD_DLL_EXPORT==1) # define ZDICTLIB_API __declspec(dllexport) ZDICTLIB_VISIBLE #elif defined(ZSTD_DLL_IMPORT) && (ZSTD_DLL_IMPORT==1) # define ZDICTLIB_API __declspec(dllimport) ZDICTLIB_VISIBLE /* It isn't required but allows to generate better code, saving a function pointer load from the IAT and an indirect jump.*/ #else # define ZDICTLIB_API ZDICTLIB_VISIBLE #endif /******************************************************************************* * Zstd dictionary builder * * FAQ * === * Why should I use a dictionary? * ------------------------------ * * Zstd can use dictionaries to improve compression ratio of small data. * Traditionally small files don't compress well because there is very little * repetition in a single sample, since it is small. But, if you are compressing * many similar files, like a bunch of JSON records that share the same * structure, you can train a dictionary on ahead of time on some samples of * these files. Then, zstd can use the dictionary to find repetitions that are * present across samples. This can vastly improve compression ratio. * * When is a dictionary useful? * ---------------------------- * * Dictionaries are useful when compressing many small files that are similar. * The larger a file is, the less benefit a dictionary will have. Generally, * we don't expect dictionary compression to be effective past 100KB. And the * smaller a file is, the more we would expect the dictionary to help. * * How do I use a dictionary? * -------------------------- * * Simply pass the dictionary to the zstd compressor with * `ZSTD_CCtx_loadDictionary()`. The same dictionary must then be passed to * the decompressor, using `ZSTD_DCtx_loadDictionary()`. There are other * more advanced functions that allow selecting some options, see zstd.h for * complete documentation. * * What is a zstd dictionary? * -------------------------- * * A zstd dictionary has two pieces: Its header, and its content. The header * contains a magic number, the dictionary ID, and entropy tables. These * entropy tables allow zstd to save on header costs in the compressed file, * which really matters for small data. The content is just bytes, which are * repeated content that is common across many samples. * * What is a raw content dictionary? * --------------------------------- * * A raw content dictionary is just bytes. It doesn't have a zstd dictionary * header, a dictionary ID, or entropy tables. Any buffer is a valid raw * content dictionary. * * How do I train a dictionary? * ---------------------------- * * Gather samples from your use case. These samples should be similar to each * other. If you have several use cases, you could try to train one dictionary * per use case. * * Pass those samples to `ZDICT_trainFromBuffer()` and that will train your * dictionary. There are a few advanced versions of this function, but this * is a great starting point. If you want to further tune your dictionary * you could try `ZDICT_optimizeTrainFromBuffer_cover()`. If that is too slow * you can try `ZDICT_optimizeTrainFromBuffer_fastCover()`. * * If the dictionary training function fails, that is likely because you * either passed too few samples, or a dictionary would not be effective * for your data. Look at the messages that the dictionary trainer printed, * if it doesn't say too few samples, then a dictionary would not be effective. * * How large should my dictionary be? * ---------------------------------- * * A reasonable dictionary size, the `dictBufferCapacity`, is about 100KB. * The zstd CLI defaults to a 110KB dictionary. You likely don't need a * dictionary larger than that. But, most use cases can get away with a * smaller dictionary. The advanced dictionary builders can automatically * shrink the dictionary for you, and select the smallest size that doesn't * hurt compression ratio too much. See the `shrinkDict` parameter. * A smaller dictionary can save memory, and potentially speed up * compression. * * How many samples should I provide to the dictionary builder? * ------------------------------------------------------------ * * We generally recommend passing ~100x the size of the dictionary * in samples. A few thousand should suffice. Having too few samples * can hurt the dictionaries effectiveness. Having more samples will * only improve the dictionaries effectiveness. But having too many * samples can slow down the dictionary builder. * * How do I determine if a dictionary will be effective? * ----------------------------------------------------- * * Simply train a dictionary and try it out. You can use zstd's built in * benchmarking tool to test the dictionary effectiveness. * * # Benchmark levels 1-3 without a dictionary * zstd -b1e3 -r /path/to/my/files * # Benchmark levels 1-3 with a dictionary * zstd -b1e3 -r /path/to/my/files -D /path/to/my/dictionary * * When should I retrain a dictionary? * ----------------------------------- * * You should retrain a dictionary when its effectiveness drops. Dictionary * effectiveness drops as the data you are compressing changes. Generally, we do * expect dictionaries to "decay" over time, as your data changes, but the rate * at which they decay depends on your use case. Internally, we regularly * retrain dictionaries, and if the new dictionary performs significantly * better than the old dictionary, we will ship the new dictionary. * * I have a raw content dictionary, how do I turn it into a zstd dictionary? * ------------------------------------------------------------------------- * * If you have a raw content dictionary, e.g. by manually constructing it, or * using a third-party dictionary builder, you can turn it into a zstd * dictionary by using `ZDICT_finalizeDictionary()`. You'll also have to * provide some samples of the data. It will add the zstd header to the * raw content, which contains a dictionary ID and entropy tables, which * will improve compression ratio, and allow zstd to write the dictionary ID * into the frame, if you so choose. * * Do I have to use zstd's dictionary builder? * ------------------------------------------- * * No! You can construct dictionary content however you please, it is just * bytes. It will always be valid as a raw content dictionary. If you want * a zstd dictionary, which can improve compression ratio, use * `ZDICT_finalizeDictionary()`. * * What is the attack surface of a zstd dictionary? * ------------------------------------------------ * * Zstd is heavily fuzz tested, including loading fuzzed dictionaries, so * zstd should never crash, or access out-of-bounds memory no matter what * the dictionary is. However, if an attacker can control the dictionary * during decompression, they can cause zstd to generate arbitrary bytes, * just like if they controlled the compressed data. * ******************************************************************************/ /*! ZDICT_trainFromBuffer(): * Train a dictionary from an array of samples. * Redirect towards ZDICT_optimizeTrainFromBuffer_fastCover() single-threaded, with d=8, steps=4, * f=20, and accel=1. * Samples must be stored concatenated in a single flat buffer `samplesBuffer`, * supplied with an array of sizes `samplesSizes`, providing the size of each sample, in order. * The resulting dictionary will be saved into `dictBuffer`. * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * Note: Dictionary training will fail if there are not enough samples to construct a * dictionary, or if most of the samples are too small (< 8 bytes being the lower limit). * If dictionary training fails, you should use zstd without a dictionary, as the dictionary * would've been ineffective anyways. If you believe your samples would benefit from a dictionary * please open an issue with details, and we can look into it. * Note: ZDICT_trainFromBuffer()'s memory usage is about 6 MB. * Tips: In general, a reasonable dictionary has a size of ~ 100 KB. * It's possible to select smaller or larger size, just by specifying `dictBufferCapacity`. * In general, it's recommended to provide a few thousands samples, though this can vary a lot. * It's recommended that total size of all samples be about ~x100 times the target size of dictionary. */ ZDICTLIB_API size_t ZDICT_trainFromBuffer(void* dictBuffer, size_t dictBufferCapacity, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples); typedef struct { int compressionLevel; /**< optimize for a specific zstd compression level; 0 means default */ unsigned notificationLevel; /**< Write log to stderr; 0 = none (default); 1 = errors; 2 = progression; 3 = details; 4 = debug; */ unsigned dictID; /**< force dictID value; 0 means auto mode (32-bits random value) * NOTE: The zstd format reserves some dictionary IDs for future use. * You may use them in private settings, but be warned that they * may be used by zstd in a public dictionary registry in the future. * These dictionary IDs are: * - low range : <= 32767 * - high range : >= (2^31) */ } ZDICT_params_t; /*! ZDICT_finalizeDictionary(): * Given a custom content as a basis for dictionary, and a set of samples, * finalize dictionary by adding headers and statistics according to the zstd * dictionary format. * * Samples must be stored concatenated in a flat buffer `samplesBuffer`, * supplied with an array of sizes `samplesSizes`, providing the size of each * sample in order. The samples are used to construct the statistics, so they * should be representative of what you will compress with this dictionary. * * The compression level can be set in `parameters`. You should pass the * compression level you expect to use in production. The statistics for each * compression level differ, so tuning the dictionary for the compression level * can help quite a bit. * * You can set an explicit dictionary ID in `parameters`, or allow us to pick * a random dictionary ID for you, but we can't guarantee no collisions. * * The dstDictBuffer and the dictContent may overlap, and the content will be * appended to the end of the header. If the header + the content doesn't fit in * maxDictSize the beginning of the content is truncated to make room, since it * is presumed that the most profitable content is at the end of the dictionary, * since that is the cheapest to reference. * * `maxDictSize` must be >= max(dictContentSize, ZSTD_DICTSIZE_MIN). * * @return: size of dictionary stored into `dstDictBuffer` (<= `maxDictSize`), * or an error code, which can be tested by ZDICT_isError(). * Note: ZDICT_finalizeDictionary() will push notifications into stderr if * instructed to, using notificationLevel>0. * NOTE: This function currently may fail in several edge cases including: * * Not enough samples * * Samples are uncompressible * * Samples are all exactly the same */ ZDICTLIB_API size_t ZDICT_finalizeDictionary(void* dstDictBuffer, size_t maxDictSize, const void* dictContent, size_t dictContentSize, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples, ZDICT_params_t parameters); /*====== Helper functions ======*/ ZDICTLIB_API unsigned ZDICT_getDictID(const void* dictBuffer, size_t dictSize); /**< extracts dictID; @return zero if error (not a valid dictionary) */ ZDICTLIB_API size_t ZDICT_getDictHeaderSize(const void* dictBuffer, size_t dictSize); /* returns dict header size; returns a ZSTD error code on failure */ ZDICTLIB_API unsigned ZDICT_isError(size_t errorCode); ZDICTLIB_API const char* ZDICT_getErrorName(size_t errorCode); #endif /* ZSTD_ZDICT_H */ #if defined(ZDICT_STATIC_LINKING_ONLY) && !defined(ZSTD_ZDICT_H_STATIC) #define ZSTD_ZDICT_H_STATIC /* This can be overridden externally to hide static symbols. */ #ifndef ZDICTLIB_STATIC_API # if defined(ZSTD_DLL_EXPORT) && (ZSTD_DLL_EXPORT==1) # define ZDICTLIB_STATIC_API __declspec(dllexport) ZDICTLIB_VISIBLE # elif defined(ZSTD_DLL_IMPORT) && (ZSTD_DLL_IMPORT==1) # define ZDICTLIB_STATIC_API __declspec(dllimport) ZDICTLIB_VISIBLE # else # define ZDICTLIB_STATIC_API ZDICTLIB_VISIBLE # endif #endif /* ==================================================================================== * The definitions in this section are considered experimental. * They should never be used with a dynamic library, as they may change in the future. * They are provided for advanced usages. * Use them only in association with static linking. * ==================================================================================== */ #define ZDICT_DICTSIZE_MIN 256 /* Deprecated: Remove in v1.6.0 */ #define ZDICT_CONTENTSIZE_MIN 128 /*! ZDICT_cover_params_t: * k and d are the only required parameters. * For others, value 0 means default. */ typedef struct { unsigned k; /* Segment size : constraint: 0 < k : Reasonable range [16, 2048+] */ unsigned d; /* dmer size : constraint: 0 < d <= k : Reasonable range [6, 16] */ unsigned steps; /* Number of steps : Only used for optimization : 0 means default (40) : Higher means more parameters checked */ unsigned nbThreads; /* Number of threads : constraint: 0 < nbThreads : 1 means single-threaded : Only used for optimization : Ignored if ZSTD_MULTITHREAD is not defined */ double splitPoint; /* Percentage of samples used for training: Only used for optimization : the first nbSamples * splitPoint samples will be used to training, the last nbSamples * (1 - splitPoint) samples will be used for testing, 0 means default (1.0), 1.0 when all samples are used for both training and testing */ unsigned shrinkDict; /* Train dictionaries to shrink in size starting from the minimum size and selects the smallest dictionary that is shrinkDictMaxRegression% worse than the largest dictionary. 0 means no shrinking and 1 means shrinking */ unsigned shrinkDictMaxRegression; /* Sets shrinkDictMaxRegression so that a smaller dictionary can be at worse shrinkDictMaxRegression% worse than the max dict size dictionary. */ ZDICT_params_t zParams; } ZDICT_cover_params_t; typedef struct { unsigned k; /* Segment size : constraint: 0 < k : Reasonable range [16, 2048+] */ unsigned d; /* dmer size : constraint: 0 < d <= k : Reasonable range [6, 16] */ unsigned f; /* log of size of frequency array : constraint: 0 < f <= 31 : 1 means default(20)*/ unsigned steps; /* Number of steps : Only used for optimization : 0 means default (40) : Higher means more parameters checked */ unsigned nbThreads; /* Number of threads : constraint: 0 < nbThreads : 1 means single-threaded : Only used for optimization : Ignored if ZSTD_MULTITHREAD is not defined */ double splitPoint; /* Percentage of samples used for training: Only used for optimization : the first nbSamples * splitPoint samples will be used to training, the last nbSamples * (1 - splitPoint) samples will be used for testing, 0 means default (0.75), 1.0 when all samples are used for both training and testing */ unsigned accel; /* Acceleration level: constraint: 0 < accel <= 10, higher means faster and less accurate, 0 means default(1) */ unsigned shrinkDict; /* Train dictionaries to shrink in size starting from the minimum size and selects the smallest dictionary that is shrinkDictMaxRegression% worse than the largest dictionary. 0 means no shrinking and 1 means shrinking */ unsigned shrinkDictMaxRegression; /* Sets shrinkDictMaxRegression so that a smaller dictionary can be at worse shrinkDictMaxRegression% worse than the max dict size dictionary. */ ZDICT_params_t zParams; } ZDICT_fastCover_params_t; /*! ZDICT_trainFromBuffer_cover(): * Train a dictionary from an array of samples using the COVER algorithm. * Samples must be stored concatenated in a single flat buffer `samplesBuffer`, * supplied with an array of sizes `samplesSizes`, providing the size of each sample, in order. * The resulting dictionary will be saved into `dictBuffer`. * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * See ZDICT_trainFromBuffer() for details on failure modes. * Note: ZDICT_trainFromBuffer_cover() requires about 9 bytes of memory for each input byte. * Tips: In general, a reasonable dictionary has a size of ~ 100 KB. * It's possible to select smaller or larger size, just by specifying `dictBufferCapacity`. * In general, it's recommended to provide a few thousands samples, though this can vary a lot. * It's recommended that total size of all samples be about ~x100 times the target size of dictionary. */ ZDICTLIB_STATIC_API size_t ZDICT_trainFromBuffer_cover( void *dictBuffer, size_t dictBufferCapacity, const void *samplesBuffer, const size_t *samplesSizes, unsigned nbSamples, ZDICT_cover_params_t parameters); /*! ZDICT_optimizeTrainFromBuffer_cover(): * The same requirements as above hold for all the parameters except `parameters`. * This function tries many parameter combinations and picks the best parameters. * `*parameters` is filled with the best parameters found, * dictionary constructed with those parameters is stored in `dictBuffer`. * * All of the parameters d, k, steps are optional. * If d is non-zero then we don't check multiple values of d, otherwise we check d = {6, 8}. * if steps is zero it defaults to its default value. * If k is non-zero then we don't check multiple values of k, otherwise we check steps values in [50, 2000]. * * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * On success `*parameters` contains the parameters selected. * See ZDICT_trainFromBuffer() for details on failure modes. * Note: ZDICT_optimizeTrainFromBuffer_cover() requires about 8 bytes of memory for each input byte and additionally another 5 bytes of memory for each byte of memory for each thread. */ ZDICTLIB_STATIC_API size_t ZDICT_optimizeTrainFromBuffer_cover( void* dictBuffer, size_t dictBufferCapacity, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples, ZDICT_cover_params_t* parameters); /*! ZDICT_trainFromBuffer_fastCover(): * Train a dictionary from an array of samples using a modified version of COVER algorithm. * Samples must be stored concatenated in a single flat buffer `samplesBuffer`, * supplied with an array of sizes `samplesSizes`, providing the size of each sample, in order. * d and k are required. * All other parameters are optional, will use default values if not provided * The resulting dictionary will be saved into `dictBuffer`. * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * See ZDICT_trainFromBuffer() for details on failure modes. * Note: ZDICT_trainFromBuffer_fastCover() requires 6 * 2^f bytes of memory. * Tips: In general, a reasonable dictionary has a size of ~ 100 KB. * It's possible to select smaller or larger size, just by specifying `dictBufferCapacity`. * In general, it's recommended to provide a few thousands samples, though this can vary a lot. * It's recommended that total size of all samples be about ~x100 times the target size of dictionary. */ ZDICTLIB_STATIC_API size_t ZDICT_trainFromBuffer_fastCover(void *dictBuffer, size_t dictBufferCapacity, const void *samplesBuffer, const size_t *samplesSizes, unsigned nbSamples, ZDICT_fastCover_params_t parameters); /*! ZDICT_optimizeTrainFromBuffer_fastCover(): * The same requirements as above hold for all the parameters except `parameters`. * This function tries many parameter combinations (specifically, k and d combinations) * and picks the best parameters. `*parameters` is filled with the best parameters found, * dictionary constructed with those parameters is stored in `dictBuffer`. * All of the parameters d, k, steps, f, and accel are optional. * If d is non-zero then we don't check multiple values of d, otherwise we check d = {6, 8}. * if steps is zero it defaults to its default value. * If k is non-zero then we don't check multiple values of k, otherwise we check steps values in [50, 2000]. * If f is zero, default value of 20 is used. * If accel is zero, default value of 1 is used. * * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * On success `*parameters` contains the parameters selected. * See ZDICT_trainFromBuffer() for details on failure modes. * Note: ZDICT_optimizeTrainFromBuffer_fastCover() requires about 6 * 2^f bytes of memory for each thread. */ ZDICTLIB_STATIC_API size_t ZDICT_optimizeTrainFromBuffer_fastCover(void* dictBuffer, size_t dictBufferCapacity, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples, ZDICT_fastCover_params_t* parameters); typedef struct { unsigned selectivityLevel; /* 0 means default; larger => select more => larger dictionary */ ZDICT_params_t zParams; } ZDICT_legacy_params_t; /*! ZDICT_trainFromBuffer_legacy(): * Train a dictionary from an array of samples. * Samples must be stored concatenated in a single flat buffer `samplesBuffer`, * supplied with an array of sizes `samplesSizes`, providing the size of each sample, in order. * The resulting dictionary will be saved into `dictBuffer`. * `parameters` is optional and can be provided with values set to 0 to mean "default". * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`) * or an error code, which can be tested with ZDICT_isError(). * See ZDICT_trainFromBuffer() for details on failure modes. * Tips: In general, a reasonable dictionary has a size of ~ 100 KB. * It's possible to select smaller or larger size, just by specifying `dictBufferCapacity`. * In general, it's recommended to provide a few thousands samples, though this can vary a lot. * It's recommended that total size of all samples be about ~x100 times the target size of dictionary. * Note: ZDICT_trainFromBuffer_legacy() will send notifications into stderr if instructed to, using notificationLevel>0. */ ZDICTLIB_STATIC_API size_t ZDICT_trainFromBuffer_legacy( void* dictBuffer, size_t dictBufferCapacity, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples, ZDICT_legacy_params_t parameters); /* Deprecation warnings */ /* It is generally possible to disable deprecation warnings from compiler, for example with -Wno-deprecated-declarations for gcc or _CRT_SECURE_NO_WARNINGS in Visual. Otherwise, it's also possible to manually define ZDICT_DISABLE_DEPRECATE_WARNINGS */ #ifdef ZDICT_DISABLE_DEPRECATE_WARNINGS # define ZDICT_DEPRECATED(message) /* disable deprecation warnings */ #else # define ZDICT_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__) # if defined (__cplusplus) && (__cplusplus >= 201402) /* C++14 or greater */ # define ZDICT_DEPRECATED(message) [[deprecated(message)]] # elif defined(__clang__) || (ZDICT_GCC_VERSION >= 405) # define ZDICT_DEPRECATED(message) __attribute__((deprecated(message))) # elif (ZDICT_GCC_VERSION >= 301) # define ZDICT_DEPRECATED(message) __attribute__((deprecated)) # elif defined(_MSC_VER) # define ZDICT_DEPRECATED(message) __declspec(deprecated(message)) # else # pragma message("WARNING: You need to implement ZDICT_DEPRECATED for this compiler") # define ZDICT_DEPRECATED(message) # endif #endif /* ZDICT_DISABLE_DEPRECATE_WARNINGS */ ZDICT_DEPRECATED("use ZDICT_finalizeDictionary() instead") ZDICTLIB_STATIC_API size_t ZDICT_addEntropyTablesFromBuffer(void* dictBuffer, size_t dictContentSize, size_t dictBufferCapacity, const void* samplesBuffer, const size_t* samplesSizes, unsigned nbSamples); #endif /* ZSTD_ZDICT_H_STATIC */ #if defined (__cplusplus) } #endif