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constify MatchState* parameter when possible

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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.
This commit is contained in:
Yann Collet
2021-09-23 08:27:44 -07:00
parent c7afbec4c1
commit fa2a4d77c7
3 changed files with 16 additions and 20 deletions
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lib/compress/zstd_compress_internal.h
+5 -5
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@@ -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;
}