summaryrefslogtreecommitdiffstats
path: root/doc/lz4_manual.html
diff options
context:
space:
mode:
Diffstat (limited to 'doc/lz4_manual.html')
-rw-r--r--doc/lz4_manual.html25
1 files changed, 13 insertions, 12 deletions
diff --git a/doc/lz4_manual.html b/doc/lz4_manual.html
index 083211d..1480089 100644
--- a/doc/lz4_manual.html
+++ b/doc/lz4_manual.html
@@ -364,23 +364,23 @@ int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
and decompression to start at beginning of the buffer.
Buffer size must feature some margin, hence be larger than final size.
- |<------------------------buffer----------------------------------->|
- |<------------compressed data---------->|
+ |<------------------------buffer--------------------------------->|
+ |<-----------compressed data--------->|
|<-----------decompressed size------------------>|
- |<-----margin----->|
+ |<----margin---->|
This technique is more useful for decompression,
since decompressed size is typically larger,
- and margin is mostly required to avoid stripe overflow, so it's short.
+ and margin is short.
In-place decompression will work inside any buffer
which size is >= LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize).
This presumes that decompressedSize > compressedSize.
Otherwise, it means compression actually expanded data,
- which can happen when data is not compressible (already compressed, or encrypted),
and it would be more efficient to store such data with a flag indicating it's not compressed.
+ This can happen when data is not compressible (already compressed, or encrypted).
- For compression, margin is larger, as it must be able to cope with both
+ For in-place compression, margin is larger, as it must be able to cope with both
history preservation, requiring input data to remain unmodified up to LZ4_DISTANCE_MAX,
and data expansion, which can happen when input is not compressible.
As a consequence, buffer size requirements are much higher,
@@ -388,10 +388,11 @@ int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
There are ways to limit this cost for compression :
- Reduce history size, by modifying LZ4_DISTANCE_MAX.
- Note that it is a compile-time constant, so all future compression will apply this parameter.
+ Note that it is a compile-time constant, so all compressions will apply this limit.
Lower values will reduce compression ratio, except when input_size < LZ4_DISTANCE_MAX,
so it's a reasonable trick when inputs are known to be small.
- Require the compressor to deliver a "maximum compressed size".
+ This is the `dstCapacity` parameter in `LZ4_compress*()`.
When this size is < LZ4_COMPRESSBOUND(inputSize), then compression can fail,
in which case, the return code will be 0 (zero).
The caller must be ready for these cases to happen,
@@ -400,16 +401,16 @@ int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
the amount of margin required for in-place compression.
In-place compression can work in any buffer
- which size is >= LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize)
+ which size is >= (maxCompressedSize)
with maxCompressedSize == LZ4_COMPRESSBOUND(srcSize) for guaranteed compression success.
- This macro depends on both maxCompressedSize and LZ4_DISTANCE_MAX,
- so there are ways to reduce memory requirements by playing with them.
+ LZ4_COMPRESS_INPLACE_BUFFER_SIZE() depends on both maxCompressedSize and LZ4_DISTANCE_MAX,
+ so it's possible to reduce memory requirements by playing with them.
</p></pre><BR>
-<pre><b>#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ( (decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) </b>/**< note: presumes that compressedSize < decompressedSize */<b>
+<pre><b>#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ((decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) </b>/**< note: presumes that compressedSize < decompressedSize. note2: margin is overestimated a bit, since it could use compressedSize instead */<b>
</b></pre><BR>
-<pre><b>#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ( (maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) </b>/**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */<b>
+<pre><b>#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ((maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) </b>/**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */<b>
</b></pre><BR>
<a name="Chapter9"></a><h2>PRIVATE DEFINITIONS</h2><pre>
Do not use these definitions directly.