Commit 7bdee465 authored by Mathis Rosenhauer's avatar Mathis Rosenhauer

Fix markdown

parent 2db4a26c
......@@ -9,22 +9,22 @@ supported, they can also be efficiently coded by grouping exponents
and mantissa.
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
[120.0-G-2][2].
## Patents
In [doc/license.txt] a clarification on potentially applying
intellectual property rights is given.
In [license.txt](doc/license.txt) a clarification on potentially
applying intellectual property rights is given.
## Installation
See [INSTALL] for details.
See [INSTALL](INSTALL) for details.
## SZIP Compatibility
[Libaec can replace SZIP][README.SZIP].
[Libaec can replace SZIP](README.SZIP).
## Encoding
......@@ -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.
Suppose you have an array of 32 bit signed integers you want to
compress. The pointer pointing to the data shall be called *source,
output goes into *dest.
compress. The pointer pointing to the data shall be called `*source`,
output goes into `*dest`.
```C++
#include <libaec.h>
......@@ -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
statistics. Larger blocks create less overhead but can be less
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
since internal buffering is based on RSI size. A smaller RSI may be
desirable in situations where each RSI will be packetized and possible
......@@ -95,41 +95,42 @@ error propagation has to be minimized.
### 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.
* 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
performance for no gain in efficiency if the data is already
uncorrelated.
* 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
* `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
architecture is big endian. Default is little endian on all
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.
* AEC_RESTRICTED: use a restricted set of code options. This option is
only valid for bits_per_sample <= 4.
* `AEC_RESTRICTED`: use a restricted set of code options. This option is
only valid for `bits_per_sample` <= 4.
* AEC_PAD_RSI: assume that the encoded RSI is padded to the next byte
boundary while decoding. The preprocessor macro ENABLE_RSI_PADDING
* `AEC_PAD_RSI`: assume that the encoded RSI is padded to the next byte
boundary while decoding. The preprocessor macro `ENABLE_RSI_PADDING`
needs to be defined while compiling for the encoder to honour this
flag.
### Data size:
The following rules apply for deducing storage size from sample size
(bits_per_sample):
(`bits_per_sample`):
|_. sample size |_. storage size|
| 1 - 8 bits | 1 byte|
| 9 - 16 bits | 2 bytes|
|17 - 24 bits | 3 bytes (only if AEC_DATA_3BYTE is set)|
|25 - 32 bits | 4 bytes (if AEC_DATA_3BYTE is set)|
|17 - 32 bits | 4 bytes (if AEC_DATA_3BYTE is not set)|
**sample size** | **storage size**
--- | ---
1 - 8 bits | 1 byte
9 - 16 bits | 2 bytes
17 - 24 bits | 3 bytes (only if `AEC_DATA_3BYTE` is 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
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
storage size in bytes. Remaining bytes which do not form a complete
sample will be ignored.
Libaec accesses next_in and next_out buffers only bytewise. There are
no alignment requirements for these buffers.
Libaec accesses `next_in` and `next_out` buffers only bytewise. There
are no alignment requirements for these buffers.
### Flushing:
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
`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
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
last call to aec_encode() must set AEC_FLUSH to drain all
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
output. aec.c is an example of streaming usage of encoding and
decoding.
### Output:
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
members and constants.
......@@ -192,12 +193,12 @@ and output is reversed.
```
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
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,
block_size, rsi, and flags are exactly the same as they were for
It is essential for decoding that parameters like `bits_per_sample`,
`block_size`, `rsi`, and `flags` are exactly the same as they were for
encoding. Libaec does not store these parameters in the coded stream
so it is up to the calling program to keep the correct parameters
between encoding and decoding.
......@@ -212,9 +213,9 @@ of the parameters.
[Consultative Committee for Space Data Systems. Lossless Data
Compression. Recommendation for Space Data System Standards, CCSDS
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
Compression. Recommendation for Space Data System Standards, CCSDS
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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