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LZHAM Codec API Reference
Note: This doc was written for the alpha version of LZHAM. I've removed the most blatant alpha version related bits, but it still needs some love.
Applications can use LZHAM by either statically linking against two LIB's named lzhamdecomp.lib and lzhamcomp.lib, or by loading a DLL named lzham_x86.dll or lzham_x64.dll.
The DLL version supports both compression/decompression. Apps that use the LIB's and don't require compression functionality only need to link with lzhamdecomp.lib. Apps that also need compression functionality must link against both libs (even if decompression functionality is not needed) because the compressor depends on functionality present in the decompression lib. (The actual library file names are lib/x86/lzhamcomp_x86.lib, lib/x64/lzhamcomp_x64.lib, etc. See the lib directory.)
Alternately, the two lib structure present in the LZHAM distribution can be discarded. It may be more convenient to just copy all .cpp/.h files in the include, lzhamcomp and lzhamdecomp directories into a single flat directory and then compile/link these files directly into the user's application.
The entire public API is defined in the single header file include/lzham.h. This is a C-style API containing functions for streaming compression/decompression, single function call compression/decompression, a function to return the codec's version, and a function that allows the user to override how the codec alllocates memory. The compression/decompression functions are somewhat similar to zlib's or LZMA's.
A set of strictly optional helper classes that simplify loading and using the DLL interface are defined in include/lzham_dynamic_lib.h and include/lzham_static_lib.h.
Currently, the only working example of the public API is in the command line test app lzhamtest/lzhamtest.cpp.
All private LZHAM code is placed in the lzham namespace. All public API's are in the global namespace and begin with the "lzham_" prefix.
The simplest way to use LZHAM is to call lzham_compress_memory() and lzham_decompress_memory(), but these API's require all data to be present in memory. For streaming, use the other API's: lzham_compress_init(), lzham_compress(), lzham_compress_deinit(), lzham_decompress_init(), lzham_decompress(), etc.
The codec is written in C++, but it only uses a subset of the full language: no exceptions, no multiple inheritance, no calls to new/delete, and very few virtuals. All memory allocation can be overriden by the user. A few templates are used, but (hopefully) in easily understood ways.
All codec state (excluding the memory allocation callback functions, which are global pointers) is stored within user-managed compression/decompression state objects (created by lzham_compress_init() or lzham_decompress_init()), so the codec is thread safe (i.e. multiple compressors/decompressors may be active simultaneously on different state objects).
However, on a single state object, the compression/decompression API's are not thread safe (i.e. the API's don't do any locking for you at the state object level). In other words, don't do something like calling lzham_compress() simultaneously from multiple threads on the same state object - bad things will happen.
The header file lzhamdecomp/lzham_core.h configures both the decompressor and compressor. The lib has been tested under Windows (x86 and x64 using VS 2008 and VS 2010), TDM GCC x86/x64, and under 32-bit Ubuntu Linux. Mac, BSD, and iOS are also supported.
The codec can be compiled under plain vanilla ANSI C/C++ by defining the LZHAM_ANSI_CPLUSPLUS macro in lzham_core.h. This shouldn't have a big impact on decompression, but this unfortunately disables all threading and atomic operations in the compressor.
lzham_uint32 lzham_get_version(void);
Returns the codec's version. The high byte contains the major version, and the low byte contains the minor version.
#define LZHAM_MIN_ALLOC_ALIGNMENT sizeof(size_t) * 2
typedef void* (*lzham_realloc_func)(void* p, size_t size, size_t* pActual_size, bool movable, void* pUser_data);
typedef size_t (*lzham_msize_func)(void* p, void* pUser_data);
void lzham_set_memory_callbacks(lzham_realloc_func pRealloc, lzham_msize_func pMSize, void* pUser_data);
By default, the codec calls the usual C-API's to manage memory (malloc, realloc, free, etc.). Call lzham_set_memory_callbacks to globally override this behavior. The user must implement two callbacks, one to handle block allocation/reallocation/freeing, and another that returns the size of allocated blocks.
Avoid calling this function if there are any currently active compression/decompression state objects. This function is not thread safe.
The custom realloc and msize functions must be implemented in a thread safe manner. These functions can be called from multiple threads when threaded compression is enabled.
All block pointers returned by the realloc callback must be aligned to at least LZHAM_MIN_ALLOC_ALIGNMENT bytes.
The custom reallocation function callback lzham_realloc_func must examine its input parameters to determine the caller's actual intent. If the input pointer p is NULL, the caller wants to allocate a block which must be at least as large as size. NULL is returned if the allocation fails.
If p is not NULL but size is 0, the caller wants to free the block pointed to by p.
Otherwise, the caller wants to attempt to change the size of the block pointed to by p. In this case, if movable is true, it is acceptable to physically move the block to satisfy the reallocation request. If movable is false, the block must not be moved. NULL is returned if reallocation fails for any reason. In this case, the original allocated block must remain allocated.
If pActual_size is not NULL, *pActual_size should be set to the actual size of the returned block.
For an example implemention, see the function lzham_default_realloc in lzhamdecomp/lzham_mem.cpp.
The custom memory size callback lzham_msize_func must return the actual size of the allocated block pointed to by p, or 0 if p is NULL. The default implementation in lzhamdecomp/lzham_mem.cpp just calls _msize.
#define LZHAM_MIN_DICT_SIZE_LOG2 15
#define LZHAM_MAX_DICT_SIZE_LOG2_X86 26
#define LZHAM_MAX_DICT_SIZE_LOG2_X64 29
Compression requires at least dict_size+65536+dict_size*4*2+65536*4 bytes of available heap memory. Under x86, the maximum supported dictionary size is 226 (64MB), and under x64 the maximum is currently 229 (512MB). The minimum supported dictionary size is 32KB, but note the codec hasn't really been tuned for max throughput or coding efficiency with tiny dictionary sizes.
#define LZHAM_MAX_HELPER_THREADS 16
The compressor can optionally create up to LZHAM_MAX_HELPER_THREADS "helper" threads to assist in compression. These helper threads can be used to accelerate parsing and match finding. Note, the original calling thread is NOT included in this total. For example, if the # of helper threads is 4, up to 5 threads total will be involved in compression (the calling thread plus 4 additional threads). Decompression is always single threaded.
enum lzham_compress_status_t
{
LZHAM_COMP_STATUS_NOT_FINISHED = 0,
LZHAM_COMP_STATUS_NEEDS_MORE_INPUT,
// All the following enums must indicate failure/success.
LZHAM_COMP_STATUS_FIRST_SUCCESS_OR_FAILURE_CODE,
LZHAM_COMP_STATUS_SUCCESS = LZHAM_COMP_STATUS_FIRST_SUCCESS_OR_FAILURE_CODE,
LZHAM_COMP_STATUS_FAILED,
LZHAM_COMP_STATUS_FAILED_INITIALIZING,
LZHAM_COMP_STATUS_INVALID_PARAMETER,
LZHAM_COMP_STATUS_OUTPUT_BUF_TOO_SMALL
};
lzham_compress_status_t defines the possible return status codes from the compressor. The first set of codes (NOT_FINISHED and NEEDS_MORE_INPUT) indicate that the compressor can't continue because the input buffer is empty, and/or the output buffer is full. The rest of the codes indicate either a success or failure condition.
enum lzham_compress_level
{
LZHAM_COMP_LEVEL_FASTEST = 0,
LZHAM_COMP_LEVEL_FASTER,
LZHAM_COMP_LEVEL_DEFAULT,
LZHAM_COMP_LEVEL_BETTER,
LZHAM_COMP_LEVEL_UBER,
LZHAM_TOTAL_COMP_LEVELS
};
lzham_compress_level allows the caller to control the tradeoff between compression ratio and throughput. LZHAM_COMP_LEVEL_FASTEST is the fastest level with the lowest compression, and LZHAM_COMP_LEVEL_UBER is the slowest level with highest compression.
enum lzham_compress_flags
{
LZHAM_COMP_FLAG_EXTREME_PARSING = 2,
LZHAM_COMP_FLAG_DETERMINISTIC_PARSING = 4,
LZHAM_COMP_FLAG_TRADEOFF_DECOMPRESSION_RATE_FOR_COMP_RATIO = 16,
};
lzham_compress_flags define the various flags that may be logically OR'd together:
LZHAM_COMP_FLAG_EXTREME_PARSING: Improves ratio by allowing the compressor's parse graph to grow "higher" (up to 4 parent nodes per output node), but is much slower.
LZHAM_COMP_FLAG_DETERMINISTIC_PARSING: Guarantees that the compressed output will always be the same given the same input data, the same compression parameters, and the same build. Otherwise, the compressed output stream may vary a small amount due to kernel threading scheduling differences between runs.
LZHAM_COMP_FLAG_TRADEOFF_DECOMPRESSION_RATE_FOR_COMP_RATIO:
If enabled, the compressor is free to use any optimizations which could lower the decompression throughput rate but improve ratio. For example, the compressor may adaptively reset the Huffman table update rate to maximum frequency if doing so would improve ratio, which is expensive for the decompressor.
struct lzham_compress_params
{
lzham_uint32 m_struct_size;
lzham_uint32 m_dict_size_log2;
lzham_compress_level m_level;
lzham_uint32 m_max_helper_threads;
lzham_uint32 m_compress_flags;
lzham_uint32 m_num_seed_bytes;
const void *m_pSeed_bytes;
};
lzham_compress_params contains various initialization parameters. The caller should clear this structure to all-0's, set m_struct_size to sizeof(lzham_compress_params}, then fill in these parameters:
m_dict_size_log2: Set to the log2(dictionary_size), must range between [LZHAM_MIN_DICT_SIZE_LOG2, LZHAM_MAX_DICT_SIZE_LOG2_X86] for x86 or LZHAM_MAX_DICT_SIZE_LOG2_X64 for x64. See Important Macros.
m_level: Compression level. Set to LZHAM_COMP_LEVEL_FASTEST, etc. See the lzham_compress_level enum.
m_max_helper_threads: Maximum # of additional "helper" threads to create, must range between [0,LZHAM_MAX_HELPER_THREADS]. See Important Macros.
m_compress_flags: Optional compression flags (see lzham_compress_flags enum)
m_num_seed_bytes: Optional, for delta compression. Set to the number of seed bytes pointed to by m_pSeed_bytes. This value must be less than or equal to the size of the dictionary size.
m_pSeed_bytes: Optional, for delta compression. Pointer to seed bytes buffer. Buffer must be at least m_num_seed_bytes long.
lzham_compress_status_t lzham_compress_memory(
const lzham_compress_params *pParams,
lzham_uint8* pDst_buf,
size_t *pDst_len,
const lzham_uint8* pSrc_buf,
size_t src_len,
lzham_uint32 *pAdler32);
Compresses source data from pSrc_buf of size src_len to pDst_buf in a single call. On entry, *pDst_len must be the size of the destination buffer. On exit, *pDst_len will contain the number of bytes written to the destination buffer. *pAdler32 will be set to the alder32 of the source data. Same return codes as lzham_compress, except this function can also return LZHAM_COMP_STATUS_OUTPUT_BUF_TOO_SMALL.
lzham_compress_state_ptr lzham_compress_init(const lzham_compress_params *pParams);
lzham_compress_init initializes a compressor. Returns a pointer to the compressor's internal state object, or NULL on failure. pParams cannot be NULL. Be sure to initialize the pParams->m_struct_size member to sizeof(lzham_compress_params) (along with the other members to reasonable values) before calling this function. Multiple state objects may be created.
lzham_uint32 lzham_compress_deinit(lzham_compress_state_ptr pState);
Deinitializes a compressor, releasing all allocated memory. Returns adler32 of source data (valid only on success).
lzham_compress_status_t lzham_compress(
lzham_compress_state_ptr pState,
const lzham_uint8 *pIn_buf, size_t *pIn_buf_size,
lzham_uint8 *pOut_buf, size_t *pOut_buf_size,
lzham_bool no_more_input_bytes_flag);
Compresses an arbitrarily sized block of data, writing as much available compressed data as possible to the output buffer. This method may be called as many times as needed (it behaves like a coroutine), but for best perf. try not to call it with tiny buffers.
pState: Pointer to internal compression state, created by lzham_compress_init.
pIn_buf, pIn_buf_size: Pointer to input data buffer, and pointer to a size_t containing the number of bytes available in this buffer. On return, *pIn_buf_size will be set to the number of bytes actually read from the buffer, which may be 0.
pOut_buf, pOut_buf_size: Pointer to the output data buffer, and a pointer to a size_t containing the max number of bytes that can be written to this buffer. On return, *pOut_buf_size will be set to the number of bytes written to this buffer, which may be 0.
no_more_input_bytes_flag: Set to true to indicate that no more input bytes are available to compress (EOF). Once you call this function with this param set to true, it must stay set to true in all future calls.
LZHAM_COMP_STATUS_NOT_FINISHED: Compression can continue, but the compressor needs more input, or it needs more room in the output buffer.
LZHAM_COMP_STATUS_NEEDS_MORE_INPUT: Compression can continue, but the compressor has no more output, and has no input but the caller has not indicated that we're at EOF. Supply more input to continue.
LZHAM_COMP_STATUS_SUCCESS: Compression has completed successfully.
LZHAM_COMP_STATUS_FAILED, LZHAM_COMP_STATUS_FAILED_INITIALIZING, LZHAM_COMP_STATUS_INVALID_PARAMETER: Something went wrong.
enum lzham_decompress_status_t
{
LZHAM_DECOMP_STATUS_NOT_FINISHED = 0,
LZHAM_DECOMP_STATUS_NEEDS_MORE_INPUT,
// All the following enums always (and MUST) indicate failure/success.
LZHAM_DECOMP_STATUS_FIRST_SUCCESS_OR_FAILURE_CODE,
LZHAM_DECOMP_STATUS_SUCCESS = LZHAM_DECOMP_STATUS_FIRST_SUCCESS_OR_FAILURE_CODE,
LZHAM_DECOMP_STATUS_FIRST_FAILURE_CODE,
LZHAM_DECOMP_STATUS_FAILED_INITIALIZING = LZHAM_DECOMP_STATUS_FIRST_FAILURE_CODE,
LZHAM_DECOMP_STATUS_FAILED_DEST_BUF_TOO_SMALL,
LZHAM_DECOMP_STATUS_FAILED_HAVE_MORE_OUTPUT,
LZHAM_DECOMP_STATUS_FAILED_EXPECTED_MORE_RAW_BYTES,
LZHAM_DECOMP_STATUS_FAILED_BAD_CODE,
LZHAM_DECOMP_STATUS_FAILED_ADLER32,
LZHAM_DECOMP_STATUS_FAILED_BAD_RAW_BLOCK,
LZHAM_DECOMP_STATUS_FAILED_BAD_COMP_BLOCK_SYNC_CHECK,
LZHAM_DECOMP_STATUS_INVALID_PARAMETER,
};
lzham_decompress_status_t defines the possible return status codes from the decompressor. The first set of codes (NOT_FINISHED and NEEDS_MORE_INPUT) indicate that the decompressor can't continue because the input buffer is empty, and/or the output buffer is full. The rest of the codes indicate either a success or failure condition.
struct lzham_decompress_params
{
lzham_uint32 m_struct_size;
lzham_uint32 m_dict_size_log2;
lzham_bool m_output_unbuffered;
lzham_bool m_compute_adler32;
lzham_uint32 m_num_seed_bytes;
const void *m_pSeed_bytes;
};
lzham_decompress_params contains various initialization parameters. The caller should clear this structure to all-0's, set m_struct_size to sizeof(lzham_decompress_params}, then fill in these parameters:
m_struct_size: Set to sizeof(lzham_decompress_params)
m_dict_size_log2: Set to the log2(dictionary_size), must range between [LZHAM_MIN_DICT_SIZE_LOG2, LZHAM_MAX_DICT_SIZE_LOG2_X86] for x86 LZHAM_MAX_DICT_SIZE_LOG2_X64 for x64. See Important Macros.
m_output_unbuffered: Set to true if the output buffer is guaranteed to be large enough to hold the entire output stream (a bit faster)
m_compute_adler32: Set to true to enable adler32 checking during decompression (slightly slower)
m_num_seed_bytes: Optional, for delta compression - number of seed bytes pointed to by m_pSeed_bytes
m_pSeed_bytes: Optional, for delta compression - pointer to seed bytes buffer, must be at least m_num_seed_bytes long
lzham_decompress_status_t lzham_decompress_memory(
const lzham_decompress_params *pParams,
lzham_uint8* pDst_buf,
size_t *pDst_len,
const lzham_uint8* pSrc_buf,
size_t src_len,
lzham_uint32 *pAdler32);
Decompresses source data from pSrc_buf of size src_len to pDst_buf in a single call. On entry, *pDst_len must be set to the size of the destination buffer. On exit, *pDst_len will be set to the actual number of bytes written to the destination buffer. *pAdler32 will be set to the alder32 of the decompressed data. Same return codes as lzham_decompress, except this function can also return LZHAM_DECOMP_STATUS_FAILED_DEST_BUF_TOO_SMALL.
lzham_decompress_state_ptr lzham_decompress_init(const lzham_decompress_params *pParams);
Initializes a decompressor. pParams cannot be NULL. Be sure to initialize the pParams->m_struct_size member to sizeof(lzham_decompress_params) (along with the other members to reasonable values) before calling this function.
Note: With large dictionaries this function could take a while (due to memory allocation). To decompress multiple independent streams, it's faster to init a decompressor state object just one time, use it, then reuse it multiple times as needed by calling lzham_decompress_reinit().
lzham_decompress_state_ptr lzham_decompress_reinit(lzham_decompress_state_ptr pState,
const lzham_decompress_params *pParams);
Quickly re-initializes the decompressor state object to its initial state (avoiding any memory allocation/freeing unless absolutely necessary).
lzham_uint32 lzham_decompress_deinit(lzham_decompress_state_ptr pState);
Deinitializes a decompressor, freeing any allocated memory associated with the state object. Returns adler32 of decompressed data if the compute_adler32 decompression parameter was true, otherwise it returns the adler32 of the source (uncompressed) data that was read from the compressed data stream.
lzham_decompress_status_t lzham_decompress(
lzham_decompress_state_ptr pState,
const lzham_uint8 *pIn_buf, size_t *pIn_buf_size,
lzham_uint8 *pOut_buf, size_t *pOut_buf_size,
lzham_bool no_more_input_bytes_flag);
Decompresses an arbitrarily sized block of compressed data, writing as much available decompressed data as possible to the output buffer. This method is implemented as a coroutine so it may be called as many times as needed. However, for best perf. try not to call it with tiny buffers.
pState: Pointer to internal decompression state, originally created by lzham_decompress_init.
pIn_buf, pIn_buf_size: Pointer to input data buffer, and a pointer to a size_t containing the number of bytes available in this buffer. On return, *pIn_buf_size will be set to the number of bytes actually read from the buffer, which may be 0.
pOut_buf, pOut_buf_size: Pointer to the output data buffer, and a pointer to a size_t containing the max number of bytes that can be written to this buffer. On return, *pOut_buf_size will be set to the number of bytes written to this buffer, which may be 0.
no_more_input_bytes_flag: Set to true to indicate that no more input bytes are available to compress (EOF). Once you call this function with this param set to true, it must remain set to true in all future calls.
Notes:
In unbuffered mode, the output buffer must be large enough to hold the entire decompressed stream. Otherwise, you'll receive the LZHAM_DECOMP_STATUS_FAILED_DEST_BUF_TOO_SMALL error (which is currently unrecoverable during unbuffered decompression).
In buffered mode, if the caller indicates the output buffer's size is 0 bytes, the caller is indicating that no more output bytes are expected from the decompressor. In this case, if the decompressor actually has more bytes available you'll receive the LZHAM_DECOMP_STATUS_FAILED_HAVE_MORE_OUTPUT error (which is recoverable in the buffered case - just call lzham_decompress() again with a non-zero size output buffer).