diff options
Diffstat (limited to 'erts')
| -rw-r--r-- | erts/doc/src/zlib.xml | 30 | ||||
| -rw-r--r-- | erts/preloaded/src/zlib.erl | 4 |
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). |