constify MatchState* parameter when possible

turns out, it's possible to constify MatchState* parameter
in some parts of the binary tree algorithm,
making it a pure read-only parameter,
as opposed to a mutable state.

This is supposed to be helpful for both maintenance and the compiler.

diff --git a/lib/compress/zstd_compress_internal.h b/lib/compress/zstd_compress_internal.h
index a5c2db4b9b04f5ee673e7668806c47dc4c065318..3dab83255e2fe3d78d97c7efb37bd1805fdff219 100644 (file)
--- a/lib/compress/zstd_compress_internal.h
+++ b/lib/compress/zstd_compress_internal.h
@@ -1228,15 +1228,15 @@ MEM_STATIC U32 ZSTD_window_update(ZSTD_window_t* window,
  */
 MEM_STATIC U32 ZSTD_getLowestMatchIndex(const ZSTD_matchState_t* ms, U32 curr, unsigned windowLog)
 {
-    U32    const maxDistance = 1U << windowLog;
-    U32    const lowestValid = ms->window.lowLimit;
-    U32    const withinWindow = (curr - lowestValid > maxDistance) ? curr - maxDistance : lowestValid;
-    U32    const isDictionary = (ms->loadedDictEnd != 0);
+    U32 const maxDistance = 1U << windowLog;
+    U32 const lowestValid = ms->window.lowLimit;
+    U32 const withinWindow = (curr - lowestValid > maxDistance) ? curr - maxDistance : lowestValid;
+    U32 const isDictionary = (ms->loadedDictEnd != 0);
     /* When using a dictionary the entire dictionary is valid if a single byte of the dictionary
      * is within the window. We invalidate the dictionary (and set loadedDictEnd to 0) when it isn't
      * valid for the entire block. So this check is sufficient to find the lowest valid match index.
      */
-    U32    const matchLowest = isDictionary ? lowestValid : withinWindow;
+    U32 const matchLowest = isDictionary ? lowestValid : withinWindow;
     return matchLowest;
 }
 

diff --git a/lib/compress/zstd_lazy.c b/lib/compress/zstd_lazy.c
index 70319d575a9a72e999a88b63ec2baad9bc6099be..ed50550f3f101fae5c5d6835ab3f9fb607470a42 100644 (file)
--- a/lib/compress/zstd_lazy.c
+++ b/lib/compress/zstd_lazy.c
@@ -61,7 +61,7 @@ ZSTD_updateDUBT(ZSTD_matchState_t* ms,
  *  assumption : curr >= btlow == (curr - btmask)
  *  doesn't fail */
 static void
-ZSTD_insertDUBT1(ZSTD_matchState_t* ms,
+ZSTD_insertDUBT1(const ZSTD_matchState_t* ms,
                  U32 curr, const BYTE* inputEnd,
                  U32 nbCompares, U32 btLow,
                  const ZSTD_dictMode_e dictMode)
@@ -151,7 +151,7 @@ ZSTD_insertDUBT1(ZSTD_matchState_t* ms,
 
 static size_t
 ZSTD_DUBT_findBetterDictMatch (
-        ZSTD_matchState_t* ms,
+        const ZSTD_matchState_t* ms,
         const BYTE* const ip, const BYTE* const iend,
         size_t* offsetPtr,
         size_t bestLength,
@@ -868,7 +868,7 @@ FORCE_INLINE_TEMPLATE size_t ZSTD_HcFindBestMatch_extDict_selectMLS (
 #define ZSTD_ROW_HASH_TAG_OFFSET 16     /* byte offset of hashes in the match state's tagTable from the beginning of a row */
 #define ZSTD_ROW_HASH_TAG_BITS 8        /* nb bits to use for the tag */
 #define ZSTD_ROW_HASH_TAG_MASK ((1u << ZSTD_ROW_HASH_TAG_BITS) - 1)
-#define ZSTD_ROW_HASH_MAX_ENTRIES 64    /* absolute maximum number of entries per row, for all configurations */               
+#define ZSTD_ROW_HASH_MAX_ENTRIES 64    /* absolute maximum number of entries per row, for all configurations */
 
 #define ZSTD_ROW_HASH_CACHE_MASK (ZSTD_ROW_HASH_CACHE_SIZE - 1)
 

diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index 40c25daa1f063743a6a3224d1831dd0a81d911ae..4c765128a15bdc654cfe5b2df12f6a4828d9a5c1 100644 (file)
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -366,7 +366,7 @@ MEM_STATIC U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
 
 /* Update hashTable3 up to ip (excluded)
    Assumption : always within prefix (i.e. not within extDict) */
-static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_matchState_t* ms,
+static U32 ZSTD_insertAndFindFirstIndexHash3 (const ZSTD_matchState_t* ms,
                                               U32* nextToUpdate3,
                                               const BYTE* const ip)
 {
@@ -396,7 +396,7 @@ static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_matchState_t* ms,
  * @param target The target of ZSTD_updateTree_internal() - we are filling to this position
  * @return : nb of positions added */
 static U32 ZSTD_insertBt1(
-                ZSTD_matchState_t* ms,
+                const ZSTD_matchState_t* ms,
                 const BYTE* const ip, const BYTE* const iend,
                 U32 const target,
                 U32 const mls, const int extDict)
@@ -421,8 +421,8 @@ static U32 ZSTD_insertBt1(
     U32* smallerPtr = bt + 2*(curr&btMask);
     U32* largerPtr  = smallerPtr + 1;
     U32 dummy32;   /* to be nullified at the end */
-    /* windowLow is based on target because we're only need positions that will be
-     * in the window at the end of the tree update.
+    /* windowLow is based on target because
+     * we only need positions that will be in the window at the end of the tree update.
      */
     U32 const windowLow = ZSTD_getLowestMatchIndex(ms, target, cParams->windowLog);
     U32 matchEndIdx = curr+8+1;
@@ -669,7 +669,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
                     return 1;
         }   }   }
         /* no dictMatchState lookup: dicts don't have a populated HC3 table */
-    }
+    }  /* if (mls == 3) */
 
     hashTable[h] = curr;   /* Update Hash Table */
 
@@ -706,8 +706,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
                | (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
                 if (dictMode == ZSTD_dictMatchState) nbCompares = 0; /* break should also skip searching dms */
                 break; /* drop, to preserve bt consistency (miss a little bit of compression) */
-            }
-        }
+        }   }
 
         if (match[matchLength] < ip[matchLength]) {
             /* match smaller than current */
@@ -752,8 +751,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
                 if ( (matchLength > ZSTD_OPT_NUM)
                    | (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
                     break;   /* drop, to guarantee consistency (miss a little bit of compression) */
-                }
-            }
+            }   }
 
             if (dictMatchIndex <= dmsBtLow) { break; }   /* beyond tree size, stop the search */
             if (match[matchLength] < ip[matchLength]) {
@@ -763,9 +761,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
                 /* match is larger than current */
                 commonLengthLarger = matchLength;
                 dictMatchIndex = nextPtr[0];
-            }
-        }
-    }
+    }   }   }  /* if (dictMode == ZSTD_dictMatchState) */
 
     assert(matchEndIdx > curr+8);
     ms->nextToUpdate = matchEndIdx - 8;  /* skip repetitive patterns */