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Mathis Rosenhauer
libaec
Commits
7bdee465
Commit
7bdee465
authored
Apr 14, 2016
by
Mathis Rosenhauer
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...
@@ -9,22 +9,22 @@ supported, they can also be efficiently coded by grouping exponents
...
@@ -9,22 +9,22 @@ supported, they can also be efficiently coded by grouping exponents
and mantissa.
and mantissa.
Libaec implements
Libaec implements
"Golomb-Rice":http://en.wikipedia.org/wiki/Golomb_coding
coding as
[
Golomb-Rice
](
http://en.wikipedia.org/wiki/Golomb_coding
)
coding as
defined in the Space Data System Standard documents
[
121.0-B-2
][
1
]
and
defined in the Space Data System Standard documents
[
121.0-B-2
][
1
]
and
[
120.0-G-2
][
2
]
.
[
120.0-G-2
][
2
]
.
## Patents
## Patents
In [
doc/license.txt] a clarification on potentially applying
In
[
license.txt
](
doc/license.txt
)
a clarification on potentially
intellectual property rights is given.
applying
intellectual property rights is given.
## Installation
## Installation
See [INSTALL] for details.
See
[
INSTALL
]
(
INSTALL
)
for details.
## SZIP Compatibility
## SZIP Compatibility
[
Libaec can replace SZIP
]
[
README.SZIP
]
.
[
Libaec can replace SZIP
]
(
README.SZIP
)
.
## Encoding
## Encoding
...
@@ -32,8 +32,8 @@ In this context efficiency refers to the size of the encoded
...
@@ -32,8 +32,8 @@ In this context efficiency refers to the size of the encoded
data. Performance refers to the time it takes to encode data.
data. Performance refers to the time it takes to encode data.
Suppose you have an array of 32 bit signed integers you want to
Suppose you have an array of 32 bit signed integers you want to
compress. The pointer pointing to the data shall be called
*
source
,
compress. The pointer pointing to the data shall be called
`*source`
,
output goes into
*
dest
.
output goes into
`*dest`
.
```
C++
```
C++
#include <libaec.h>
#include <libaec.h>
...
@@ -82,12 +82,12 @@ output goes into *dest.
...
@@ -82,12 +82,12 @@ output goes into *dest.
...
...
```
```
block_size
can vary from 8 to 64 samples. Smaller blocks allow the
`block_size`
can vary from 8 to 64 samples. Smaller blocks allow the
compression to adapt more rapidly to changing source
compression to adapt more rapidly to changing source
statistics. Larger blocks create less overhead but can be less
statistics. Larger blocks create less overhead but can be less
efficient if source statistics change across the block.
efficient if source statistics change across the block.
rsi
sets the reference sample interval. A large RSI will improve
`rsi`
sets the reference sample interval. A large RSI will improve
performance and efficiency. It will also increase memory requirements
performance and efficiency. It will also increase memory requirements
since internal buffering is based on RSI size. A smaller RSI may be
since internal buffering is based on RSI size. A smaller RSI may be
desirable in situations where each RSI will be packetized and possible
desirable in situations where each RSI will be packetized and possible
...
@@ -95,41 +95,42 @@ error propagation has to be minimized.
...
@@ -95,41 +95,42 @@ error propagation has to be minimized.
### Flags:
### Flags:
*
AEC_DATA_SIGNED
: input data are signed integers. Specifying this
*
`AEC_DATA_SIGNED`
: input data are signed integers. Specifying this
correctly increases compression efficiency. Default is unsigned.
correctly increases compression efficiency. Default is unsigned.
*
AEC_DATA_PREPROCESS
: preprocessing input will improve compression
*
`AEC_DATA_PREPROCESS`
: preprocessing input will improve compression
efficiency if data samples are correlated. It will only cost
efficiency if data samples are correlated. It will only cost
performance for no gain in efficiency if the data is already
performance for no gain in efficiency if the data is already
uncorrelated.
uncorrelated.
*
AEC_DATA_MSB
: input data is stored most significant byte first
*
`AEC_DATA_MSB`
: input data is stored most significant byte first
i.e. big endian. You have to specify
AEC_DATA_MSB
even if your host
i.e. big endian. You have to specify
`AEC_DATA_MSB`
even if your host
architecture is big endian. Default is little endian on all
architecture is big endian. Default is little endian on all
architectures.
architectures.
*
AEC_DATA_3BYTE
: the 17 to 24 bit input data is stored in three
*
`AEC_DATA_3BYTE`
: the 17 to 24 bit input data is stored in three
bytes. This flag has no effect for other sample sizes.
bytes. This flag has no effect for other sample sizes.
*
AEC_RESTRICTED
: use a restricted set of code options. This option is
*
`AEC_RESTRICTED`
: use a restricted set of code options. This option is
only valid for
bits_per_sample
<= 4.
only valid for
`bits_per_sample`
<= 4.
*
AEC_PAD_RSI
: assume that the encoded RSI is padded to the next byte
*
`AEC_PAD_RSI`
: assume that the encoded RSI is padded to the next byte
boundary while decoding. The preprocessor macro
ENABLE_RSI_PADDING
boundary while decoding. The preprocessor macro
`ENABLE_RSI_PADDING`
needs to be defined while compiling for the encoder to honour this
needs to be defined while compiling for the encoder to honour this
flag.
flag.
### Data size:
### Data size:
The following rules apply for deducing storage size from sample size
The following rules apply for deducing storage size from sample size
(
bits_per_sample
):
(
`bits_per_sample`
):
|_. sample size |_. storage size|
**sample size**
|
**storage size**
| 1 - 8 bits | 1 byte|
--- | ---
| 9 - 16 bits | 2 bytes|
1 - 8 bits | 1 byte
|17 - 24 bits | 3 bytes (only if AEC_DATA_3BYTE is set)|
9 - 16 bits | 2 bytes
|25 - 32 bits | 4 bytes (if AEC_DATA_3BYTE is set)|
17 - 24 bits | 3 bytes (only if
`AEC_DATA_3BYTE`
is set)
|17 - 32 bits | 4 bytes (if AEC_DATA_3BYTE is not set)|
25 - 32 bits | 4 bytes (if
`AEC_DATA_3BYTE`
is set)
17 - 32 bits | 4 bytes (if
`AEC_DATA_3BYTE`
is not set)
If a sample requires less bits than the storage size provides, then
If a sample requires less bits than the storage size provides, then
you have to make sure that unused bits are not set. Libaec does not
you have to make sure that unused bits are not set. Libaec does not
...
@@ -138,23 +139,23 @@ if unused bits are set. All input data must be a multiple of the
...
@@ -138,23 +139,23 @@ if unused bits are set. All input data must be a multiple of the
storage size in bytes. Remaining bytes which do not form a complete
storage size in bytes. Remaining bytes which do not form a complete
sample will be ignored.
sample will be ignored.
Libaec accesses
next_in and next_out buffers only bytewise. There a
re
Libaec accesses
`next_in`
and
`next_out`
buffers only bytewise. The
re
no alignment requirements for these buffers.
are
no alignment requirements for these buffers.
### Flushing:
### Flushing:
aec_encode
can be used in a streaming fashion by chunking input and
`aec_encode`
can be used in a streaming fashion by chunking input and
output and specifying
AEC_NO_FLUSH
. The function will return if either
output and specifying
`AEC_NO_FLUSH`
. The function will return if either
the input runs empty or the output buffer is full. The calling
the input runs empty or the output buffer is full. The calling
function can check
avail_in and avail_out
to see what occurred. The
function can check
`avail_in`
and
`avail_out`
to see what occurred. The
last call to
aec_encode() must set AEC_FLUSH
to drain all
last call to
`aec_encode()`
must set
`AEC_FLUSH`
to drain all
output. aec.c is an example of streaming usage of encoding and
output. aec.c is an example of streaming usage of encoding and
decoding.
decoding.
### Output:
### Output:
Encoded data will be written to the buffer submitted with
Encoded data will be written to the buffer submitted with
next_out. The length of the compressed data is total_out
.
`next_out`
. The length of the compressed data is
`total_out`
.
See libaec.h for a detailed description of all relevant structure
See libaec.h for a detailed description of all relevant structure
members and constants.
members and constants.
...
@@ -192,12 +193,12 @@ and output is reversed.
...
@@ -192,12 +193,12 @@ and output is reversed.
```
```
It is strongly recommended that the size of the output buffer
It is strongly recommended that the size of the output buffer
(
next_out
) is a multiple of the storage size in bytes. If the buffer
(
`next_out`
) is a multiple of the storage size in bytes. If the buffer
is not a multiple of the storage size and the buffer gets filled to
is not a multiple of the storage size and the buffer gets filled to
the last sample, the error code
AEC_MEM_ERROR
is returned.
the last sample, the error code
`AEC_MEM_ERROR`
is returned.
It is essential for decoding that parameters like
bits_per_sample
,
It is essential for decoding that parameters like
`bits_per_sample`
,
block_size, rsi, and flags
are exactly the same as they were for
`block_size`
,
`rsi`
, and
`flags`
are exactly the same as they were for
encoding. Libaec does not store these parameters in the coded stream
encoding. Libaec does not store these parameters in the coded stream
so it is up to the calling program to keep the correct parameters
so it is up to the calling program to keep the correct parameters
between encoding and decoding.
between encoding and decoding.
...
@@ -212,9 +213,9 @@ of the parameters.
...
@@ -212,9 +213,9 @@ of the parameters.
[
Consultative Committee for Space Data Systems. Lossless Data
[
Consultative Committee for Space Data Systems. Lossless Data
Compression. Recommendation for Space Data System Standards, CCSDS
Compression. Recommendation for Space Data System Standards, CCSDS
121.0-B-2. Blue Book. Issue 2. Washington, D.C.: CCSDS, May 2012.
][
1
]
121.0-B-2. Blue Book. Issue 2. Washington, D.C.: CCSDS, May 2012.
][
1
]
[1] http://public.ccsds.org/publications/archive/121x0b2.pdf
[
1
]
:
http://public.ccsds.org/publications/archive/121x0b2.pdf
[
Consultative Committee for Space Data Systems. Lossless Data
[
Consultative Committee for Space Data Systems. Lossless Data
Compression. Recommendation for Space Data System Standards, CCSDS
Compression. Recommendation for Space Data System Standards, CCSDS
120.0-G-3. Green Book. Issue 3. Washington, D.C.: CCSDS, April 2013.
][
2
]
120.0-G-3. Green Book. Issue 3. Washington, D.C.: CCSDS, April 2013.
][
2
]
[2] http://public.ccsds.org/publications/archive/120x0g3.pdf
[
2
]
:
http://public.ccsds.org/publications/archive/120x0g3.pdf
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