From: Yann Collet <yann.collet.73@gmail.com>
Date: Sat, 8 Feb 2025 01:15:24 +0000 (-0800)
Subject: updated LDM documentation
X-Git-Tag: v1.5.7^2~4^2~7
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bf218c142aade4aa842205e93bc8260dcbfb372d;p=thirdparty%2Fzstd.git

updated LDM documentation
---

diff --git a/programs/fileio.c b/programs/fileio.c
index 1b8aa8a99..0ecca40d2 100644
--- a/programs/fileio.c
+++ b/programs/fileio.c
@@ -1100,11 +1100,12 @@ static void FIO_adjustParamsForPatchFromMode(FIO_prefs_t* const prefs,
         FIO_setLdmFlag(prefs, 1);
     }
     if (cParams.strategy >= ZSTD_btopt) {
-        DISPLAYLEVEL(3, "[Optimal parser notes] Consider the following to improve patch size at the cost of speed:\n");
-        DISPLAYLEVEL(3, "- Use --single-thread mode in the zstd cli\n");
-        DISPLAYLEVEL(3, "- Set a larger targetLength (e.g. --zstd=targetLength=4096)\n");
-        DISPLAYLEVEL(3, "- Set a larger chainLog (e.g. --zstd=chainLog=%u)\n", ZSTD_CHAINLOG_MAX);
-        DISPLAYLEVEL(3, "Also consider playing around with searchLog and hashLog\n");
+        DISPLAYLEVEL(4, "[Optimal parser notes] Consider the following to improve patch size at the cost of speed:\n");
+        DISPLAYLEVEL(4, "- Set a larger targetLength (e.g. --zstd=targetLength=4096)\n");
+        DISPLAYLEVEL(4, "- Set a larger chainLog (e.g. --zstd=chainLog=%u)\n", ZSTD_CHAINLOG_MAX);
+        DISPLAYLEVEL(4, "- Set a larger LDM hashLog (e.g. --zstd=ldmHashLog=%u)\n", ZSTD_LDM_HASHLOG_MAX);
+        DISPLAYLEVEL(4, "- Set a smaller LDM rateLog (e.g. --zstd=ldmHashRateLog=%u)\n", ZSTD_LDM_HASHRATELOG_MIN);
+        DISPLAYLEVEL(4, "Also consider playing around with searchLog and hashLog\n");
     }
 }
 
diff --git a/programs/zstd.1.md b/programs/zstd.1.md
index 29b7a5bb7..be2179e5d 100644
--- a/programs/zstd.1.md
+++ b/programs/zstd.1.md
@@ -455,6 +455,17 @@ The list of available _options_:
     Value 0 is special and means "default": _ovlog_ is automatically determined by `zstd`.
     In which case, _ovlog_ will range from 6 to 9, depending on selected _strat_.
 
+- `ldmHashRateLog`=_lhrlog_, `lhrlog`=_lhrlog_:
+    Specify the frequency of inserting entries into the long distance matching
+    hash table.
+
+    This option is ignored unless long distance matching is enabled.
+
+    Larger values will improve compression speed. Deviating far from the
+    default value will likely result in a decrease in compression ratio.
+
+    The default value varies between 4 and 8, depending on `strategy`.
+
 - `ldmHashLog`=_lhlog_, `lhlog`=_lhlog_:
     Specify the maximum size for a hash table used for long distance matching.
 
@@ -463,7 +474,7 @@ The list of available _options_:
     Bigger hash tables usually improve compression ratio at the expense of more
     memory during compression and a decrease in compression speed.
 
-    The minimum _lhlog_ is 6 and the maximum is 30 (default: 20).
+    The minimum _lhlog_ is 6 and the maximum is 30 (default: `windowLog - ldmHashRateLog`).
 
 - `ldmMinMatch`=_lmml_, `lmml`=_lmml_:
     Specify the minimum searched length of a match for long distance matching.
@@ -472,7 +483,7 @@ The list of available _options_:
 
     Larger/very small values usually decrease compression ratio.
 
-    The minimum _lmml_ is 4 and the maximum is 4096 (default: 64).
+    The minimum _lmml_ is 4 and the maximum is 4096 (default: 32 to 128, depending on `strategy`).
 
 - `ldmBucketSizeLog`=_lblog_, `lblog`=_lblog_:
     Specify the size of each bucket for the hash table used for long distance
@@ -483,18 +494,8 @@ The list of available _options_:
     Larger bucket sizes improve collision resolution but decrease compression
     speed.
 
-    The minimum _lblog_ is 1 and the maximum is 8 (default: 3).
-
-- `ldmHashRateLog`=_lhrlog_, `lhrlog`=_lhrlog_:
-    Specify the frequency of inserting entries into the long distance matching
-    hash table.
-
-    This option is ignored unless long distance matching is enabled.
-
-    Larger values will improve compression speed. Deviating far from the
-    default value will likely result in a decrease in compression ratio.
+    The minimum _lblog_ is 1 and the maximum is 8 (default: 4 to 8, depending on `strategy`).
 
-    The default value is `wlog - lhlog`.
 
 ### Example
 The following parameters sets advanced compression options to something