@@ -2,16 +2,20 @@ LZ4 - Library Files
22================================
33
44The ` /lib ` directory contains many files, but depending on project's objectives,
5- not all of them are necessary.
5+ not all of them are required.
6+ Limited systems may want to reduce the nb of source files to include
7+ as a way to reduce binary size and dependencies.
68
7- #### Minimal LZ4 build
9+ Capabilities are added at the "level" granularity, detailed below.
10+
11+ #### Level 1 : Minimal LZ4 build
812
913The minimum required is ** ` lz4.c ` ** and ** ` lz4.h ` ** ,
1014which provides the fast compression and decompression algorithms.
1115They generate and decode data using the [ LZ4 block format] .
1216
1317
14- #### High Compression variant
18+ #### Level 2 : High Compression variant
1519
1620For more compression ratio at the cost of compression speed,
1721the High Compression variant called ** lz4hc** is available.
@@ -20,22 +24,37 @@ This variant also compresses data using the [LZ4 block format],
2024and depends on regular ` lib/lz4.* ` source files.
2125
2226
23- #### Frame support, for interoperability
27+ #### Level 3 : Frame support, for interoperability
2428
2529In order to produce compressed data compatible with ` lz4 ` command line utility,
2630it's necessary to use the [ official interoperable frame format] .
2731This format is generated and decoded automatically by the ** lz4frame** library.
2832Its public API is described in ` lib/lz4frame.h ` .
2933In order to work properly, lz4frame needs all other modules present in ` /lib ` ,
3034including, lz4 and lz4hc, and also ** xxhash** .
31- So it's necessary to include all ` *.c ` and ` *.h ` files present in ` /lib ` .
35+ So it's necessary to also include ` xxhash.c ` and ` xxhash.h ` .
36+
37+
38+ #### Level 4 : File compression operations
39+
40+ As a helper around file operations,
41+ the library has been recently extended with ` lz4file.c ` and ` lz4file.h `
42+ (still considered experimental at the time of this writing).
43+ These helpers allow opening, reading, writing, and closing files
44+ using transparent LZ4 compression / decompression.
45+ As a consequence, using ` lz4file ` adds a dependency on ` <stdio.h> ` .
46+
47+ ` lz4file ` relies on ` lz4frame ` in order to produce compressed data
48+ conformant to the [ LZ4 Frame format] specification.
49+ Consequently, to enable this capability,
50+ it's necessary to include all ` *.c ` and ` *.h ` files from ` lib/ ` directory.
3251
3352
3453#### Advanced / Experimental API
3554
3655Definitions which are not guaranteed to remain stable in future versions,
3756are protected behind macros, such as ` LZ4_STATIC_LINKING_ONLY ` .
38- As the name strongly implies , these definitions should only be invoked
57+ As the name suggests , these definitions should only be invoked
3958in the context of static linking *** only*** .
4059Otherwise, dependent application may fail on API or ABI break in the future.
4160The associated symbols are also not exposed by the dynamic library by default.
@@ -58,7 +77,7 @@ The following build macro can be selected to adjust source code behavior at comp
5877 Set to 65535 by default, which is the maximum value supported by lz4 format.
5978 Reducing maximum distance will reduce opportunities for LZ4 to find matches,
6079 hence will produce a worse compression ratio.
61- However, a smaller max distance can allow compatibility with specific decoders using limited memory budget.
80+ Setting a smaller max distance could allow compatibility with specific decoders with limited memory budget.
6281 This build macro only influences the compressed output of the compressor.
6382
6483- ` LZ4_DISABLE_DEPRECATE_WARNINGS ` : invoking a deprecated function will make the compiler generate a warning.
@@ -69,22 +88,34 @@ The following build macro can be selected to adjust source code behavior at comp
6988 This build macro offers another project-specific method
7089 by defining ` LZ4_DISABLE_DEPRECATE_WARNINGS ` before including the LZ4 header files.
7190
72- - ` LZ4_USER_MEMORY_FUNCTIONS ` : replace calls to <stdlib >'s ` malloc ` , ` calloc ` and ` free `
73- by user-defined functions, which must be called ` LZ4_malloc() ` , ` LZ4_calloc() ` and ` LZ4_free() ` .
74- User functions must be available at link time.
75-
7691- ` LZ4_FORCE_SW_BITCOUNT ` : by default, the compression algorithm tries to determine lengths
7792 by using bitcount instructions, generally implemented as fast single instructions in many cpus.
7893 In case the target cpus doesn't support it, or compiler intrinsic doesn't work, or feature bad performance,
7994 it's possible to use an optimized software path instead.
80- This is achieved by setting this build macros .
95+ This is achieved by setting this build macros.
8196 In most cases, it's not expected to be necessary,
8297 but it can be legitimately considered for less common platforms.
8398
8499- ` LZ4_ALIGN_TEST ` : alignment test ensures that the memory area
85100 passed as argument to become a compression state is suitably aligned.
86101 This test can be disabled if it proves flaky, by setting this value to 0.
87102
103+ - ` LZ4_USER_MEMORY_FUNCTIONS ` : replace calls to ` <stdlib,h> ` 's ` malloc() ` , ` calloc() ` and ` free() `
104+ by user-defined functions, which must be named ` LZ4_malloc() ` , ` LZ4_calloc() ` and ` LZ4_free() ` .
105+ User functions must be available at link time.
106+
107+ - ` LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION ` :
108+ Remove support of dynamic memory allocation.
109+ For more details, see description of this macro in ` lib/lz4.c ` .
110+
111+ - ` LZ4_FREESTANDING ` : by setting this build macro to 1,
112+ LZ4/HC removes dependencies on the C standard library,
113+ including allocation functions and ` memmove() ` , ` memcpy() ` , and ` memset() ` .
114+ This build macro is designed to help use LZ4/HC in restricted environments
115+ (embedded, bootloader, etc).
116+ For more details, see description of this macro in ` lib/lz4.h ` .
117+
118+
88119
89120#### Amalgamation
90121
@@ -101,7 +132,7 @@ All `*.h` files present in `/lib` remain necessary to compile `lz4_all.c`.
101132
102133DLL can be created using MinGW+MSYS with the ` make liblz4 ` command.
103134This command creates ` dll\liblz4.dll ` and the import library ` dll\liblz4.lib ` .
104- To override the ` dlltool ` command when cross-compiling on Linux, just set the ` DLLTOOL ` variable. Example of cross compilation on Linux with mingw-w64 64 bits:
135+ To override the ` dlltool ` command when cross-compiling on Linux, just set the ` DLLTOOL ` variable. Example of cross compilation on Linux with mingw-w64 64 bits:
105136```
106137make BUILD_STATIC=no CC=x86_64-w64-mingw32-gcc DLLTOOL=x86_64-w64-mingw32-dlltool OS=Windows_NT
107138```
@@ -127,6 +158,7 @@ Other files present in the directory are not source code. They are :
127158 - ` README.md ` : this file
128159
129160[ official interoperable frame format ] : ../doc/lz4_Frame_format.md
161+ [ LZ4 Frame format ] : ../doc/lz4_Frame_format.md
130162[ LZ4 block format ] : ../doc/lz4_Block_format.md
131163
132164
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