Add the 'rle' zstrategy

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).