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authorBjörn Gustavsson <[email protected]>2014-01-16 12:16:39 +0100
committerBjörn Gustavsson <[email protected]>2014-01-16 12:26:05 +0100
commit1101fcb3e61634f1be92e1b9ba9fad5a11b8554a (patch)
tree2ec4ef83558ed4d7200c8bc94bdc63c6a746fe60 /erts
parent8a147a73651713efebb9ac973f618a6d66685eca (diff)
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Add the 'rle' zstrategy
Diffstat (limited to 'erts')
-rw-r--r--erts/doc/src/zlib.xml30
-rw-r--r--erts/preloaded/src/zlib.erl4
2 files changed, 19 insertions, 15 deletions
diff --git a/erts/doc/src/zlib.xml b/erts/doc/src/zlib.xml
index afc597b729..11a7437f5a 100644
--- a/erts/doc/src/zlib.xml
+++ b/erts/doc/src/zlib.xml
@@ -161,20 +161,22 @@ list_to_binary([Compressed|Last])</pre>
state. <c><anno>MemLevel</anno></c>=1 uses minimum memory but is slow and
reduces compression ratio; <c><anno>MemLevel</anno></c>=9 uses maximum
memory for optimal speed. The default value is 8.</p>
- <p>The <c><anno>Strategy</anno></c> parameter is used to tune the
- compression algorithm. Use the value <c>default</c> for
- normal data, <c>filtered</c> for data produced by a filter
- (or predictor), or <c>huffman_only</c> to force Huffman
- encoding only (no string match). Filtered data consists
- mostly of small values with a somewhat random
- distribution. In this case, the compression algorithm is
- tuned to compress them better. The effect of
- <c>filtered</c>is to force more Huffman coding and less
- string matching; it is somewhat intermediate between
- <c>default</c> and <c>huffman_only</c>. The <c><anno>Strategy</anno></c>
- parameter only affects the compression ratio but not the
- correctness of the compressed output even if it is not set
- appropriately.</p>
+ <p>The <c><anno>Strategy</anno></c> parameter is used to tune
+ the compression algorithm. Use the value <c>default</c> for
+ normal data, <c>filtered</c> for data produced by a filter (or
+ predictor), <c>huffman_only</c> to force Huffman encoding
+ only (no string match), or <c>rle</c> to limit match
+ distances to one (run-length encoding). Filtered data
+ consists mostly of small values with a somewhat random
+ distribution. In this case, the compression algorithm is tuned
+ to compress them better. The effect of <c>filtered</c>is to
+ force more Huffman coding and less string matching; it is
+ somewhat intermediate between <c>default</c> and
+ <c>huffman_only</c>. <c>rle</c> is designed to be almost as
+ fast as <c>huffman_only</c>, but give better compression for PNG
+ image data. The <c><anno>Strategy</anno></c> parameter only
+ affects the compression ratio but not the correctness of the
+ compressed output even if it is not set appropriately.</p>
</desc>
</func>
<func>
diff --git a/erts/preloaded/src/zlib.erl b/erts/preloaded/src/zlib.erl
index 3d85533b80..df7b2e6198 100644
--- a/erts/preloaded/src/zlib.erl
+++ b/erts/preloaded/src/zlib.erl
@@ -47,6 +47,7 @@
%% compresssion strategy
-define(Z_FILTERED, 1).
-define(Z_HUFFMAN_ONLY, 2).
+-define(Z_RLE, 3).
-define(Z_DEFAULT_STRATEGY, 0).
%% deflate compression method
@@ -125,7 +126,7 @@
-type zmethod() :: 'deflated'.
-type zwindowbits() :: -15..-9 | 9..47.
-type zmemlevel() :: 1..9.
--type zstrategy() :: 'default' | 'filtered' | 'huffman_only'.
+-type zstrategy() :: 'default' | 'filtered' | 'huffman_only' | 'rle'.
%%------------------------------------------------------------------------
@@ -486,6 +487,7 @@ arg_level(_) -> erlang:error(badarg).
arg_strategy(filtered) -> ?Z_FILTERED;
arg_strategy(huffman_only) -> ?Z_HUFFMAN_ONLY;
+arg_strategy(rle) -> ?Z_RLE;
arg_strategy(default) -> ?Z_DEFAULT_STRATEGY;
arg_strategy(_) -> erlang:error(badarg).