sync with zlib.h

ok jmc

diff --git a/lib/libz/compress.3 b/lib/libz/compress.3
index 96db2af..73d21d5 100644 (file)
--- a/lib/libz/compress.3
+++ b/lib/libz/compress.3
@@ -1,4 +1,4 @@
-.\"    $OpenBSD: compress.3,v 1.26 2024/01/20 11:16:27 tb Exp $
+.\"    $OpenBSD: compress.3,v 1.27 2024/02/07 20:51:38 tb Exp $
 .\"
 .\"  Copyright (C) 1995-2017 Jean-loup Gailly and Mark Adler
 .\"
@@ -23,7 +23,7 @@
 .\"
 .\" This page corresponds to zlib version 1.2.3
 .\"
-.Dd $Mdocdate: January 20 2024 $
+.Dd $Mdocdate: February 7 2024 $
 .Dt COMPRESS 3
 .Os
 .Sh NAME
@@ -1127,33 +1127,41 @@ for normal data;
 .Dv Z_FILTERED
 for data produced by a filter
 .Pq or predictor ;
-.Dv Z_HUFFMAN_ONLY
-to force Huffman encoding only
-.Pq no string match ,
-or
 .Dv Z_RLE
 to limit match distances to one
-.Pq run-length encoding .
+.Pq run-length encoding ,
+or
+.Dv Z_HUFFMAN_ONLY
+to force Huffman encoding only
+.Pq no string match .
 Filtered data consists mostly of small values with a
-somewhat random distribution.
+somewhat random distribution,
+as produced by the PNG filters.
 In this case, the compression algorithm is tuned to compress them better.
 The effect of
 .Dv Z_FILTERED
-is to force more Huffman coding and less string matching;
-it is somewhat intermediate between
+is to force more Huffman coding and less string matching than the default;
+it is intermediate between
 .Dv Z_DEFAULT_STRATEGY
 and
 .Dv Z_HUFFMAN_ONLY .
 .Dv Z_RLE
-is designed to be almost as fast as
+is almost as fast as
 .Dv Z_HUFFMAN_ONLY ,
-but gives better compression for PNG image data.
+but should give better compression for PNG image data than Huffman only.
+The degree of string matching from most to none is:
+.Dv Z_DEFAULT_STRATEGY ,
+.Dv Z_FILTERED ,
+.Dv Z_RLE ,
+then
+.Dv Z_HUFFMAN .
 The
 .Fa strategy
-parameter only affects the compression ratio but not the correctness of the
-compressed output, even if it is not set appropriately.
+parameter affects the compression ratio but never the correctness of the
+compressed output, even if it is not set optimally for the given data.
 .Dv Z_FIXED
-prevents the use of dynamic Huffman codes,
+uses the default string matching,
+but prevents the use of dynamic Huffman codes,
 allowing for a simpler decoder for special applications.
 .Pp
 .Fn deflateInit2