data compression library for embedded/real-time systems

heatshrink

A data compression/decompression library for embedded/real-time systems.

Key Features:

  • Low memory usage (as low as 50 bytes) It is useful for some cases with less than 50 bytes, and useful for many general cases with < 300 bytes.
  • Incremental, bounded CPU use You can chew on input data in arbitrarily tiny bites. This is a useful property in hard real-time environments.
  • Can use either static or dynamic memory allocation The library doesn't impose any constraints on memory management.
  • ISC license You can use it freely, even for commercial purposes.

Getting Started:

There is a standalone command-line program, heatshrink, but the encoder and decoder can also be used as libraries, independent of each other. To do so, copy heatshrink_common.h, heatshrink_config.h, and either heatshrink_encoder.c or heatshrink_decoder.c (and their respective header) into your project. For projects that use both, static libraries are built that use static and dynamic allocation.

Dynamic allocation is used by default, but in an embedded context, you probably want to statically allocate the encoder/decoder. Set HEATSHRINK_DYNAMIC_ALLOC to 0 in heatshrink_config.h.

Basic Usage

  1. Allocate a heatshrink_encoder or heatshrink_decoder state machine using their alloc function, or statically allocate one and call their reset function to initialize them. (See below for configuration options.)

  2. Use sink to sink an input buffer into the state machine. The input_size pointer argument will be set to indicate how many bytes of the input buffer were actually consumed. (If 0 bytes were conusmed, the buffer is full.)

  3. Use poll to move output from the state machine into an output buffer. The output_size pointer argument will be set to indicate how many bytes were output, and the function return value will indicate whether further output is available. (The state machine may not output any data until it has received enough input.)

Repeat steps 2 and 3 to stream data through the state machine. Since it's doing data compression, the input and output sizes can vary significantly. Looping will be necessary to buffer the input and output as the data is processed.

  1. When the end of the input stream is reached, call finish to notify the state machine that no more input is available. The return value from finish will indicate whether any output remains. if so, call poll to get more.

Continue calling finish and polling to flush remaining output until finish indicates that the output has been exhausted.

Sinking more data after finish has been called will not work without calling reset on the state machine.

Configuration

heatshrink has a couple configuration options, which impact its resource usage and how effectively it can compress data. These are set when dynamically allocating an encoder or decoder, or in heatshrink_config.h if they are statically allocated.

  • window_sz2, -w in the CLI: Set the window size to 2^W bytes.

The window size determines how far back in the input can be searched for repeated patterns. A window_sz2 of 8 will only use 256 bytes (2^8), while a window_sz2 of 10 will use 1024 bytes (2^10). The latter uses more memory, but may also compress more effectively by detecting more repetition.

The window_sz2 setting currently must be between 4 and 15.

  • lookahead_sz2, -l in the CLI: Set the lookahead size to 2^L bytes.

The lookahead size determines the max length for repeated patterns that are found. If the lookahead_sz2 is 4, a 50-byte run of 'a' characters will be represented as several repeated 16-byte patterns (2^4 is 16), whereas a larger lookahead_sz2 may be able to represent it all at once. The number of bits used for the lookahead size is fixed, so an overly large lookahead size can reduce compression by adding unused size bits to small patterns.

The lookahead_sz2 setting currently must be between 3 and the window_sz2 - 1.

  • input_buffer_size - How large an input buffer to use for the decoder. This impacts how much work the decoder can do in a single step, and a larger buffer will use more memory. An extremely small buffer (say, 1 byte) will add overhead due to lots of suspend/resume function calls, but should not change how well data compresses.

Recommended Defaults

For embedded/low memory contexts, a window_sz2 in the 8 to 10 range is probably a good default, depending on how tight memory is. Smaller or larger window sizes may make better trade-offs in specific circumstances, but should be checked with representative data.

The lookahead_sz2 should probably start near the window_sz2/2, e.g. -w 8 -l 4 or -w 10 -l 5. The command-line program can be used to measure how well test data works with different settings.

More Information and Benchmarks:

heatshrink is based on LZSS, since it's particularly suitable for compression in small amounts of memory. It can use an optional, small index to make compression significantly faster, but otherwise can run in under 100 bytes of memory. The index currently adds 2^(window size+1) bytes to memory usage for compression, and temporarily allocates 512 bytes on the stack during index construction (if the index is enabled).

For more information, see the blog post for an overview, and the heatshrink_encoder.h / heatshrink_decoder.h header files for API documentation.

Build Status

Build Status

Comments
  • Fail to decompress buffer

    Fail to decompress buffer

    This is really strange, I am able to compress but fail to decompress a "specific" set of data buffer. I am using static linking with following configuration:

    #define HEATSHRINK_STATIC_INPUT_BUFFER_SIZE 512
    #define HEATSHRINK_STATIC_WINDOW_BITS 10
    #define HEATSHRINK_STATIC_LOOKAHEAD_BITS 3
    
    uint8_t compressed[] = {
    0x80, 0x80, 0x35, 0x45, 0x01, 0x7B, 0xA9, 0x07, 0x01, 0xF4, 0x01, 0xB0, 0x00, 0xE0, 0xA0, 0x0D, 
    0x45, 0x80, 0x5E, 0x82, 0x00, 0x35, 0xA8, 0xB7, 0x4F, 0x7E, 0x10, 0x89, 0x10, 0x03, 0x33, 0x3A, 
    0x2C, 0xBA, 0x21, 0x7C, 0x04, 0x87, 0xE1, 0x42, 0xB2, 0x7C, 0xE7, 0xFF, 0x88, 0x70, 0x26, 0x20, 
    0x00, 0xC2, 0xE0, 0x70, 0x10, 0x16, 0x82, 0x9F, 0x00, 0x1C, 0x00, 0x70
    };
    
    /* Actual input */
    uint8_t decompressed[] = {
    0x01, 0x00, 0x00, 0x00, 0x45, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xD4, 0x07, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, 0x16, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0xA8, 0x6E, 0x3D, 0xF0, 0x08, 0x22, 0x3D, 0xF0, 0x33, 0x45, 0x2E, 0x10, 0x7C, 0x01, 0x00, 0xF0, 0x42, 0x64, 0xF3, 0x3F, 0xF8, 0x0E, 0x00, 0x05, 0x05, 0x05, 0x0B, 0x03, 0x01, 0x64, 0xF3, 0x3F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
    };
    

    I have also attached my test application. So problem is:

    If I try to "only" decompress the compressed buffer, I run into a never ending loop of poll. However if I first compress the "decompressed" buffer and then decompress in the same application everything works. I am not able to understand why?

    to check both usecases, make if 0 @line 202 to 1

    test_heatshrink.txt

    PS: Rename file to .c

  • Static and dynamic versions of heatshrink aren't compatible

    Static and dynamic versions of heatshrink aren't compatible

    The static and dynamic versions of heatshrink don't create the same output.

    1. I had to fix some compilation issues c.f. https://github.com/sjaeckel/heatshrink/tree/fix/static
      • Now both test targets and heatshrink compile fine. Tests pass.
    2. To reproduce that the created files from static and dynamic versions are not the same:
      1. Build heatshrink in default (dynamic) configuration and compress a file with parameters "-i 32 -w 8", the default settings of the static configuration.
      2. Build heatshrink with HEATSHRINK_DYNAMIC_ALLOC 0 and compress the same file.

    Resulting files won't be the same! Is this intentional?

  • Add option to override heatshrink configuration

    Add option to override heatshrink configuration

    Currently its impossible to change heatshrink compression configuration wihout touching the library header files. This patch makes it possible for configuration which can be configured at compilation time without having to touch the library. Which makes it easier to keep it sync with github source without modifying the actual source.

    Signed-off-by: Ajay Bhargav [email protected]

  • Java library

    Java library

    Hi, thanks for your great work! I would like to decompress the data generated by an embedded system on Java. Have you got a ready-to-use solution? Should i use a standard lzss java class?

    Thanks

  • Possible data loss at stream end in -w4 -l2

    Possible data loss at stream end in -w4 -l2

    I got an excellent bug report from @unixdj with detailed, minimal steps to reproduce data loss at the end of the stream:

    $ echo -n aaaa | ./heatshrink -e -w4 -l2 | ./heatshrink -d -w4 -l2
    a   # should be "aaaa"
    

    A regression test has been added.

    This is not currently known to occur under any other combinations of settings except -w4 -l2, the absolute minimum.

    A change that fixes this without breaking reverse compatibility would be strongly preferred.

  • Compiling for ESP8266 fails

    Compiling for ESP8266 fails

    Hey,

    I've just tried to use the library on a ESP8266 platform. Sadly there are several errors displayed in heatshrink.c:

    Error GCC invalid conversion from 'void*' to 'io_handle*' [-fpermissive] 121:37 Error GCC 'heatshrink_encoder_alloc' was not declared in this scope 282:86 Error GCC 'heatshrink_encoder_free' was not declared in this scope 305:32 Error GCC 'heatshrink_decoder_alloc' was not declared in this scope 352:39 Error GCC 'heatshrink_decoder_free' was not declared in this scope 382:32

    Any help is appreciated :)

  • Fixed fallthrough compiler warning

    Fixed fallthrough compiler warning

    Fixed fallthrough warnings thrown in GCC 7.1.1:

    heatshrink_encoder.c: In function ‘heatshrink_encoder_poll’:
    heatshrink_encoder.c:237:24: warning: this statement may fall through [-Wimplicit-fallthrough=]
                 hse->state = st_flush_bit_buffer(hse, &oi);
                 ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    heatshrink_encoder.c:238:9: note: here
             case HSES_DONE:
    
    
    heatshrink.c: In function ‘proc_args’:
    heatshrink.c:411:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
                 usage();
                 ^~~~~~~
    heatshrink.c:412:9: note: here
             case 'e':               /* encode */
    
    
  • Make heatshrink compile with std=c99 and using getopt().

    Make heatshrink compile with std=c99 and using getopt().

    The current target 'make heatshrink' results in "warning: implicit declaration of function ‘getopt’" and undeclared variable errors. The -std=c99 prevents <unistd.h> from including <getopt.h> which makes the compile fail.

    Including getopt.h additionally resolves this issue (as -std=gnu99 or -D_GNU_SOURCE is not a nice option).

  • unable to decode the compressed file based on command tool

    unable to decode the compressed file based on command tool

    ./test -e -v acc1.txt acc1.z acc1.txt 70.92 % 27301 -> 7940 (-w 11 -l 4)

    ./test -d -v acc1.z acc1.unz ... -- popping 4 bit(s) -- pulled byte 0x49 -- accumulated 00000004 -- backref count (lsb), got 0x0004 (+1) Segmentation fault: 11

  • heatshrink binary only decompresses the first block

    heatshrink binary only decompresses the first block

    After patching Heatshrink with the changes in #7 and building with MinGW (gcc 4.7.2), a valid "heatshrink.exe" executable is produced, but this binary fails to decompress data correctly.

    $ ./heatshrink.exe -ev LICENSE LICENSE.enc
    
    $ ./heatshrink.exe -dv LICENSE.enc LICENSE.dec
    
    $ md5sum LICENSE*
    cd12e61f206f9ee1a6622d0df2f773d1 *LICENSE
    e7e84c0c9268751994a1830f9b98d399 *LICENSE.dec
    81239e24ddf1a6dde9d5cff95d186911 *LICENSE.enc
    
    $ ls -l LICENSE*
    -rw-r--r-- 1 ppemberton Administrators 784 Dec 12 15:11 LICENSE
    -rw-r--r-- 1 ppemberton Administrators 387 Dec 22 11:41 LICENSE.dec
    -rw-r--r-- 1 ppemberton Administrators 681 Dec 22 11:41 LICENSE.enc
    

    It appears that the decode step is only processing the first block of data in the file.

    Interestingly the byte counts in verbose mode are wrong too:

    $ ./heatshrink.exe -ev LICENSE LICENSE.enc
    LICENSE 14.29 %  784 -> 672 (-w 11 -l 4)
    
    $ ./heatshrink.exe -dv LICENSE.enc LICENSE.dec
    LICENSE.enc -3.27 %      367 -> 379 (-w 11 -l 4)
    
  • Decoder for JavaScript?

    Decoder for JavaScript?

    I would like to encode with heatsink a bitmap image data on a micro-controller and display it in the browser.
    Therefore my question is: is there a JavaScript implementation of the decoder?

  • Fix indexing for platforms where char size is larger than a byte

    Fix indexing for platforms where char size is larger than a byte

    On platforms where the minimum memory access size is larger than a byte (case in point, μ'nSP where each address refers to one 16-bit word rather than a byte), indexing would never work due to the index buffer being initialized improperly. Instead of each element being initialized to -1 as would typically happen on a system with byte sized access, it gets initialized to 255. This breaks the indexing logic and causes it to go into an infinite loop.

    This patch changes the initializer from 0xff to -1, so depending on the platform it should always initialize the entire array with -1. On byte access systems, memset() will truncate the -1 to 0xff as per standard, which results in the same desired behavior.

  • Usage simplified if heatshrink_encoder_poll() returns HSER_POLL_MORE when finish flag is set and output buffer is full

    Usage simplified if heatshrink_encoder_poll() returns HSER_POLL_MORE when finish flag is set and output buffer is full

    heatshrink_encoder_poll() is returning 'HSER_POLL_EMPTY' rather than 'HSER_POLL_MORE' when finishing and the output buffer is full. Is a break missing from the 'HSES_FLUSH_BITS' case? As implemented, it is dropping through to the 'HSES_DONE' case and returning 'HSER_POLL_EMPTY' rather than running through the 'HSER_POLL_MORE' check?

        case HSES_FLUSH_BITS:
            hse->state = st_flush_bit_buffer(hse, &oi);
        case HSES_DONE:
            return HSER_POLL_EMPTY;
        default:
            LOG("-- bad state %s\n", state_names[hse->state]);
            return HSER_POLL_ERROR_MISUSE;
        }
    
        if (hse->state == in_state) {
            /* Check if output buffer is exhausted. */
            if (*output_size == out_buf_size) return HSER_POLL_MORE;
        }
    

    Logging without break:

    heatshrink_encoder_poll()
    (12:59:37.602) (>>) -- polling, state 1 (filled), flags 0x01<LF>
    ...
    (13:00:37.174) (>>) -- polling, state 2 (search), flags 0x01<LF>
    (13:00:37.174) (>>) ## step_search, scan @ +963 (1927/2048), input size 964<LF>
    (13:00:37.199) (>>) -- scanning for match of buf[1987:1988] between buf[963:1987] (max 1 bytes)<LF>
    (13:00:37.199) (>>) -- none found<LF>
    (13:00:37.230) (>>) ss Match not found<LF>
    (13:00:37.230) (>>) -- polling, state 3 (yield_tag_bit), flags 0x01<LF>
    (13:00:37.230) (>>) -- adding tag bit: 1<LF>
    (13:00:37.230) (>>) ++ push_bits: 1 bits, input of 0x01<LF>
    (13:00:37.293) (>>) -- polling, state 4 (yield_literal), flags 0x01<LF>
    (13:00:37.293) (>>) -- yielded literal byte 0x44 ('D') from +1987<LF>
    (13:00:37.293) (>>) ++ push_bits: 8 bits, input of 0x44<LF>
    (13:00:37.293) (>>)  > pushing byte 0x75<LF>
    (13:00:37.293) (>>) -- polling, state 2 (search), flags 0x01<LF>
    (13:00:37.293) (>>) ## step_search, scan @ +964 (1928/2048), input size 964<LF>
    (13:00:37.323) (>>) -- end of search @ 964<LF>
    (13:00:37.323) (>>) -- polling, state 8 (flush_bits), flags 0x01<LF>
    returns HSER_POLL_EMPTY
    

    I observe the desired behaviour with:

        case HSES_FLUSH_BITS:
            hse->state = st_flush_bit_buffer(hse, &oi);
            break;
    

    Logging with break:

    heatshrink_encoder_poll()
    (13:15:58.567) (>>) -- polling, state 1 (filled), flags 0x01<LF>
    ...
    (13:17:46.218) (>>) -- polling, state 2 (search), flags 0x01<LF>
    (13:17:46.218) (>>) ## step_search, scan @ +963 (1927/2048), input size 964<LF>
    (13:17:46.218) (>>) -- scanning for match of buf[1987:1988] between buf[963:1987] (max 1 bytes)<LF>
    (13:17:46.227) (>>) -- none found<LF>
    (13:17:46.227) (>>) ss Match not found<LF>
    (13:17:46.227) (>>) -- polling, state 3 (yield_tag_bit), flags 0x01<LF>
    (13:17:46.227) (>>) -- adding tag bit: 1<LF>
    (13:17:46.258) (>>) ++ push_bits: 1 bits, input of 0x01<LF>
    (13:17:46.258) (>>) -- polling, state 4 (yield_literal), flags 0x01<LF>
    (13:17:46.258) (>>) -- yielded literal byte 0x44 ('D') from +1987<LF>
    (13:17:46.289) (>>) ++ push_bits: 8 bits, input of 0x44<LF>
    (13:17:46.289) (>>)  > pushing byte 0x75<LF>
    (13:17:46.289) (>>) -- polling, state 2 (search), flags 0x01<LF>
    (13:17:46.289) (>>) ## step_search, scan @ +964 (1928/2048), input size 964<LF>
    (13:17:46.362) (>>) -- end of search @ 964<LF>
    (13:17:46.362) (>>) -- polling, state 8 (flush_bits), flags 0x01<LF>
    returns HSDR_POLL_MORE
    
    heatshrink_encoder_poll()
    (13:17:46.362) (>>) -- polling, state 8 (flush_bits), flags 0x01<LF>
    (13:17:46.362) (>>) -- flushing remaining byte (bit_index == 0x02)<LF>
    (13:17:46.382) (>>) -- done!<LF>
    (13:17:46.382) (>>) -- polling, state 9 (done), flags 0x01<LF>
    returns HSER_POLL_EMPTY
    

    This behaviour is not seen in the example usage, since heatshrink_decoder_poll is also called until 'poll_sz == 0', rather than just until pres != HSDR_POLL_MORE.

    If heatshrink_encoder_poll() is returns 'HSER_POLL_MORE' when finishing and the output buffer is full, the usage can be simplified by only needing to call heatshrink_decoder_finish() once to set the finish flag. If it returns 'HSDR_FINISH_MORE', keep calling heatshrink_encoder_poll() until it returns 'HSER_POLL_EMPTY' i.e. same as when sinking.

    Pseudo code without error handling:

    do
    {
    	if (input remaining)
    	{
    		heatshrink_encoder_sink()
    		update input remaining
    	}
    	
    	if (no input remaining)
    	{
    		fres = heatshrink_encoder_finish()
    		if (fres == HSER_FINISH_DONE)
    		{
    			return
    		}
    	}
    	
    	do 
    	{
    		pres = heatshrink_encoder_poll()
    		write output
    	} while (pres == HSER_POLL_MORE);
    } while (input remaining)
    

    I believe the encoder example in the following pull request has an issue without changing the fall-through to a break in the 'HSES_FLUSH_BITS' case, as this is what I based my implementation on i.e. a single call to heatshrink_encoder_finish(): https://github.com/atomicobject/heatshrink/pull/54/commits

  • heatshrink_encoder_sink doesn't behave as documented

    heatshrink_encoder_sink doesn't behave as documented

    Hi,

    for sink the Readme states "If 0 bytes were conusmed, the buffer is full." (with typo). However the function complains about misuse instead https://github.com/atomicobject/heatshrink/blob/7d419e1fa4830d0b919b9b6a91fe2fb786cf3280/heatshrink_encoder.c#L147

  • Fallthrough in usage should be `break`

    Fallthrough in usage should be `break`

    While looking through my local changes I noticed a small difference between the local changes and the upstream develop branch:

    https://github.com/atomicobject/heatshrink/blob/ffd95059ff9155fa373b3e6276854db3ad7b4e3c/src/heatshrink.c#L410-L412

    In my local version I imported the fix for #46 using a break in that place, which is IMHO the more natural choice, as you normally don't expect the usage() display to cause any side-effects on your program configuration, thus resulting in the following code locally instead:

            case 'h':               /* help */
                usage();
                break;
    

    Given that usage() internally calls exit(1); this is even stranger, as this comment causes the expectation of the code continuing after the call to usage(); returns.

  • Compatibility on PIC32

    Compatibility on PIC32

    Hi,

    does this code work on PIC32 microcontrollers.

    I found some of the dependency files are missing ( like.... getopt.h, err.h... etc) Could you please inform whether it works on PIC32?

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